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postgresql/src/backend/optimizer/util/placeholder.c

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Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
/*-------------------------------------------------------------------------
*
* placeholder.c
* PlaceHolderVar and PlaceHolderInfo manipulation routines
*
*
Update copyright for 2019 Backpatch-through: certain files through 9.4
2019-01-02 18:44:25 +01:00
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
Remove cvs keywords from all files.
2010-09-20 22:08:53 +02:00
* src/backend/optimizer/util/placeholder.c
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "nodes/nodeFuncs.h"
Add an explicit representation of the output targetlist to Paths. Up to now, there's been an assumption that all Paths for a given relation compute the same output column set (targetlist). However, there are good reasons to remove that assumption. For example, an indexscan on an expression index might be able to return the value of an expensive function "for free". While we have the ability to generate such a plan today in simple cases, we don't have a way to model that it's cheaper than a plan that computes the function from scratch, nor a way to create such a plan in join cases (where the function computation would normally happen at the topmost join node). Also, we need this so that we can have Paths representing post-scan/join steps, where the targetlist may well change from one step to the next. Therefore, invent a "struct PathTarget" representing the columns we expect a plan step to emit. It's convenient to include the output tuple width and tlist evaluation cost in this struct, and there will likely be additional fields in future. While Path nodes that actually do have custom outputs will need their own PathTargets, it will still be true that most Paths for a given relation will compute the same tlist. To reduce the overhead added by this patch, keep a "default PathTarget" in RelOptInfo, and allow Paths that compute that column set to just point to their parent RelOptInfo's reltarget. (In the patch as committed, actually every Path is like that, since we do not yet have any cases of custom PathTargets.) I took this opportunity to provide some more-honest costing of PlaceHolderVar evaluation. Up to now, the assumption that "scan/join reltargetlists have cost zero" was applied not only to Vars, where it's reasonable, but also PlaceHolderVars where it isn't. Now, we add the eval cost of a PlaceHolderVar's expression to the first plan level where it can be computed, by including it in the PathTarget cost field and adding that to the cost estimates for Paths. This isn't perfect yet but it's much better than before, and there is a way forward to improve it more. This costing change affects the join order chosen for a couple of the regression tests, changing expected row ordering.
2016-02-19 02:01:49 +01:00
#include "optimizer/cost.h"
Refactor planner's header files. Create a new header optimizer/optimizer.h, which exposes just the planner functions that can be used "at arm's length", without need to access Paths or the other planner-internal data structures defined in nodes/relation.h. This is intended to provide the whole planner API seen by most of the rest of the system; although FDWs still need to use additional stuff, and more thought is also needed about just what selfuncs.c should rely on. The main point of doing this now is to limit the amount of new #include baggage that will be needed by "planner support functions", which I expect to introduce later, and which will be in relevant datatype modules rather than anywhere near the planner. This commit just moves relevant declarations into optimizer.h from other header files (a couple of which go away because everything got moved), and adjusts #include lists to match. There's further cleanup that could be done if we want to decide that some stuff being exposed by optimizer.h doesn't belong in the planner at all, but I'll leave that for another day. Discussion: https://postgr.es/m/11460.1548706639@sss.pgh.pa.us
2019-01-29 21:48:51 +01:00
#include "optimizer/optimizer.h"
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
#include "optimizer/pathnode.h"
#include "optimizer/placeholder.h"
#include "optimizer/planmain.h"
#include "utils/lsyscache.h"
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
/* Local functions */
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
static void find_placeholders_recurse(PlannerInfo *root, Node *jtnode);
static void find_placeholders_in_expr(PlannerInfo *root, Node *expr);
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
/*
* make_placeholder_expr
Dept of better ideas: refrain from creating the planner's placeholder_list until vars are distributed to rels during query_planner() startup. We don't really need it before that, and not building it early has some advantages. First, we don't need to put it through the various preprocessing steps, which saves some cycles and eliminates the need for a number of routines to support PlaceHolderInfo nodes at all. Second, this means one less unused plan for any sub-SELECT appearing in a placeholder's expression, since we don't build placeholder_list until after sublink expansion is complete.
2008-10-22 22:17:52 +02:00
* Make a PlaceHolderVar for the given expression.
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
*
* phrels is the syntactic location (as a set of baserels) to attribute
* to the expression.
*/
PlaceHolderVar *
make_placeholder_expr(PlannerInfo *root, Expr *expr, Relids phrels)
{
PlaceHolderVar *phv = makeNode(PlaceHolderVar);
phv->phexpr = expr;
phv->phrels = phrels;
phv->phid = ++(root->glob->lastPHId);
phv->phlevelsup = 0;
return phv;
}
/*
* find_placeholder_info
Fix nested PlaceHolderVar expressions that appear only in targetlists. A PlaceHolderVar's expression might contain another, lower-level PlaceHolderVar. If the outer PlaceHolderVar is used, the inner one certainly will be also, and so we have to make sure that both of them get into the placeholder_list with correct ph_may_need values during the initial pre-scan of the query (before deconstruct_jointree starts). We did this correctly for PlaceHolderVars appearing in the query quals, but overlooked the issue for those appearing in the top-level targetlist; with the result that nested placeholders referenced only in the targetlist did not work correctly, as illustrated in bug #6154. While at it, add some error checking to find_placeholder_info to ensure that we don't try to create new placeholders after it's too late to do so; they have to all be created before deconstruct_jointree starts. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2011-08-09 06:48:51 +02:00
* Fetch the PlaceHolderInfo for the given PHV
*
* If the PlaceHolderInfo doesn't exist yet, create it if create_new_ph is
* true, else throw an error.
Dept of better ideas: refrain from creating the planner's placeholder_list until vars are distributed to rels during query_planner() startup. We don't really need it before that, and not building it early has some advantages. First, we don't need to put it through the various preprocessing steps, which saves some cycles and eliminates the need for a number of routines to support PlaceHolderInfo nodes at all. Second, this means one less unused plan for any sub-SELECT appearing in a placeholder's expression, since we don't build placeholder_list until after sublink expansion is complete.
2008-10-22 22:17:52 +02:00
*
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
* This is separate from make_placeholder_expr because subquery pullup has
* to make PlaceHolderVars for expressions that might not be used at all in
* the upper query, or might not remain after const-expression simplification.
* We build PlaceHolderInfos only for PHVs that are still present in the
* simplified query passed to query_planner().
*
pgindent run for 9.4 This includes removing tabs after periods in C comments, which was applied to back branches, so this change should not effect backpatching.
2014-05-06 18:12:18 +02:00
* Note: this should only be called after query_planner() has started. Also,
Change TRUE/FALSE to true/false The lower case spellings are C and C++ standard and are used in most parts of the PostgreSQL sources. The upper case spellings are only used in some files/modules. So standardize on the standard spellings. The APIs for ICU, Perl, and Windows define their own TRUE and FALSE, so those are left as is when using those APIs. In code comments, we use the lower-case spelling for the C concepts and keep the upper-case spelling for the SQL concepts. Reviewed-by: Michael Paquier <michael.paquier@gmail.com>
2017-08-16 06:22:32 +02:00
* create_new_ph must not be true after deconstruct_jointree begins, because
Fix nested PlaceHolderVar expressions that appear only in targetlists. A PlaceHolderVar's expression might contain another, lower-level PlaceHolderVar. If the outer PlaceHolderVar is used, the inner one certainly will be also, and so we have to make sure that both of them get into the placeholder_list with correct ph_may_need values during the initial pre-scan of the query (before deconstruct_jointree starts). We did this correctly for PlaceHolderVars appearing in the query quals, but overlooked the issue for those appearing in the top-level targetlist; with the result that nested placeholders referenced only in the targetlist did not work correctly, as illustrated in bug #6154. While at it, add some error checking to find_placeholder_info to ensure that we don't try to create new placeholders after it's too late to do so; they have to all be created before deconstruct_jointree starts. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2011-08-09 06:48:51 +02:00
* make_outerjoininfo assumes that we already know about all placeholders.
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
*/
PlaceHolderInfo *
Fix nested PlaceHolderVar expressions that appear only in targetlists. A PlaceHolderVar's expression might contain another, lower-level PlaceHolderVar. If the outer PlaceHolderVar is used, the inner one certainly will be also, and so we have to make sure that both of them get into the placeholder_list with correct ph_may_need values during the initial pre-scan of the query (before deconstruct_jointree starts). We did this correctly for PlaceHolderVars appearing in the query quals, but overlooked the issue for those appearing in the top-level targetlist; with the result that nested placeholders referenced only in the targetlist did not work correctly, as illustrated in bug #6154. While at it, add some error checking to find_placeholder_info to ensure that we don't try to create new placeholders after it's too late to do so; they have to all be created before deconstruct_jointree starts. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2011-08-09 06:48:51 +02:00
find_placeholder_info(PlannerInfo *root, PlaceHolderVar *phv,
bool create_new_ph)
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
{
Dept of better ideas: refrain from creating the planner's placeholder_list until vars are distributed to rels during query_planner() startup. We don't really need it before that, and not building it early has some advantages. First, we don't need to put it through the various preprocessing steps, which saves some cycles and eliminates the need for a number of routines to support PlaceHolderInfo nodes at all. Second, this means one less unused plan for any sub-SELECT appearing in a placeholder's expression, since we don't build placeholder_list until after sublink expansion is complete.
2008-10-22 22:17:52 +02:00
PlaceHolderInfo *phinfo;
Fix planner problems with LATERAL references in PlaceHolderVars. The planner largely failed to consider the possibility that a PlaceHolderVar's expression might contain a lateral reference to a Var coming from somewhere outside the PHV's syntactic scope. We had a previous report of a problem in this area, which I tried to fix in a quick-hack way in commit 4da6439bd8553059766011e2a42c6e39df08717f, but Antonin Houska pointed out that there were still some problems, and investigation turned up other issues. This patch largely reverts that commit in favor of a more thoroughly thought-through solution. The new theory is that a PHV's ph_eval_at level cannot be higher than its original syntactic level. If it contains lateral references, those don't change the ph_eval_at level, but rather they create a lateral-reference requirement for the ph_eval_at join relation. The code in joinpath.c needs to handle that. Another issue is that createplan.c wasn't handling nested PlaceHolderVars properly. In passing, push knowledge of lateral-reference checks for join clauses into join_clause_is_movable_to. This is mainly so that FDWs don't need to deal with it. This patch doesn't fix the original join-qual-placement problem reported by Jeremy Evans (and indeed, one of the new regression test cases shows the wrong answer because of that). But the PlaceHolderVar problems need to be fixed before that issue can be addressed, so committing this separately seems reasonable.
2013-08-18 02:22:37 +02:00
Relids rels_used;
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
ListCell *lc;
/* if this ever isn't true, we'd need to be able to look in parent lists */
Assert(phv->phlevelsup == 0);
foreach(lc, root->placeholder_list)
{
Dept of better ideas: refrain from creating the planner's placeholder_list until vars are distributed to rels during query_planner() startup. We don't really need it before that, and not building it early has some advantages. First, we don't need to put it through the various preprocessing steps, which saves some cycles and eliminates the need for a number of routines to support PlaceHolderInfo nodes at all. Second, this means one less unused plan for any sub-SELECT appearing in a placeholder's expression, since we don't build placeholder_list until after sublink expansion is complete.
2008-10-22 22:17:52 +02:00
phinfo = (PlaceHolderInfo *) lfirst(lc);
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
if (phinfo->phid == phv->phid)
return phinfo;
}
Dept of better ideas: refrain from creating the planner's placeholder_list until vars are distributed to rels during query_planner() startup. We don't really need it before that, and not building it early has some advantages. First, we don't need to put it through the various preprocessing steps, which saves some cycles and eliminates the need for a number of routines to support PlaceHolderInfo nodes at all. Second, this means one less unused plan for any sub-SELECT appearing in a placeholder's expression, since we don't build placeholder_list until after sublink expansion is complete.
2008-10-22 22:17:52 +02:00
/* Not found, so create it */
Fix nested PlaceHolderVar expressions that appear only in targetlists. A PlaceHolderVar's expression might contain another, lower-level PlaceHolderVar. If the outer PlaceHolderVar is used, the inner one certainly will be also, and so we have to make sure that both of them get into the placeholder_list with correct ph_may_need values during the initial pre-scan of the query (before deconstruct_jointree starts). We did this correctly for PlaceHolderVars appearing in the query quals, but overlooked the issue for those appearing in the top-level targetlist; with the result that nested placeholders referenced only in the targetlist did not work correctly, as illustrated in bug #6154. While at it, add some error checking to find_placeholder_info to ensure that we don't try to create new placeholders after it's too late to do so; they have to all be created before deconstruct_jointree starts. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2011-08-09 06:48:51 +02:00
if (!create_new_ph)
elog(ERROR, "too late to create a new PlaceHolderInfo");
Dept of better ideas: refrain from creating the planner's placeholder_list until vars are distributed to rels during query_planner() startup. We don't really need it before that, and not building it early has some advantages. First, we don't need to put it through the various preprocessing steps, which saves some cycles and eliminates the need for a number of routines to support PlaceHolderInfo nodes at all. Second, this means one less unused plan for any sub-SELECT appearing in a placeholder's expression, since we don't build placeholder_list until after sublink expansion is complete.
2008-10-22 22:17:52 +02:00
phinfo = makeNode(PlaceHolderInfo);
phinfo->phid = phv->phid;
phinfo->ph_var = copyObject(phv);
Fix planner problems with LATERAL references in PlaceHolderVars. The planner largely failed to consider the possibility that a PlaceHolderVar's expression might contain a lateral reference to a Var coming from somewhere outside the PHV's syntactic scope. We had a previous report of a problem in this area, which I tried to fix in a quick-hack way in commit 4da6439bd8553059766011e2a42c6e39df08717f, but Antonin Houska pointed out that there were still some problems, and investigation turned up other issues. This patch largely reverts that commit in favor of a more thoroughly thought-through solution. The new theory is that a PHV's ph_eval_at level cannot be higher than its original syntactic level. If it contains lateral references, those don't change the ph_eval_at level, but rather they create a lateral-reference requirement for the ph_eval_at join relation. The code in joinpath.c needs to handle that. Another issue is that createplan.c wasn't handling nested PlaceHolderVars properly. In passing, push knowledge of lateral-reference checks for join clauses into join_clause_is_movable_to. This is mainly so that FDWs don't need to deal with it. This patch doesn't fix the original join-qual-placement problem reported by Jeremy Evans (and indeed, one of the new regression test cases shows the wrong answer because of that). But the PlaceHolderVar problems need to be fixed before that issue can be addressed, so committing this separately seems reasonable.
2013-08-18 02:22:37 +02:00
/*
* Any referenced rels that are outside the PHV's syntactic scope are
* LATERAL references, which should be included in ph_lateral but not in
pgindent run for 9.4 This includes removing tabs after periods in C comments, which was applied to back branches, so this change should not effect backpatching.
2014-05-06 18:12:18 +02:00
* ph_eval_at. If no referenced rels are within the syntactic scope,
Fix planner problems with LATERAL references in PlaceHolderVars. The planner largely failed to consider the possibility that a PlaceHolderVar's expression might contain a lateral reference to a Var coming from somewhere outside the PHV's syntactic scope. We had a previous report of a problem in this area, which I tried to fix in a quick-hack way in commit 4da6439bd8553059766011e2a42c6e39df08717f, but Antonin Houska pointed out that there were still some problems, and investigation turned up other issues. This patch largely reverts that commit in favor of a more thoroughly thought-through solution. The new theory is that a PHV's ph_eval_at level cannot be higher than its original syntactic level. If it contains lateral references, those don't change the ph_eval_at level, but rather they create a lateral-reference requirement for the ph_eval_at join relation. The code in joinpath.c needs to handle that. Another issue is that createplan.c wasn't handling nested PlaceHolderVars properly. In passing, push knowledge of lateral-reference checks for join clauses into join_clause_is_movable_to. This is mainly so that FDWs don't need to deal with it. This patch doesn't fix the original join-qual-placement problem reported by Jeremy Evans (and indeed, one of the new regression test cases shows the wrong answer because of that). But the PlaceHolderVar problems need to be fixed before that issue can be addressed, so committing this separately seems reasonable.
2013-08-18 02:22:37 +02:00
* force evaluation at the syntactic location.
*/
rels_used = pull_varnos((Node *) phv->phexpr);
phinfo->ph_lateral = bms_difference(rels_used, phv->phrels);
if (bms_is_empty(phinfo->ph_lateral))
Phase 2 of pgindent updates. Change pg_bsd_indent to follow upstream rules for placement of comments to the right of code, and remove pgindent hack that caused comments following #endif to not obey the general rule. Commit e3860ffa4dd0dad0dd9eea4be9cc1412373a8c89 wasn't actually using the published version of pg_bsd_indent, but a hacked-up version that tried to minimize the amount of movement of comments to the right of code. The situation of interest is where such a comment has to be moved to the right of its default placement at column 33 because there's code there. BSD indent has always moved right in units of tab stops in such cases --- but in the previous incarnation, indent was working in 8-space tab stops, while now it knows we use 4-space tabs. So the net result is that in about half the cases, such comments are placed one tab stop left of before. This is better all around: it leaves more room on the line for comment text, and it means that in such cases the comment uniformly starts at the next 4-space tab stop after the code, rather than sometimes one and sometimes two tabs after. Also, ensure that comments following #endif are indented the same as comments following other preprocessor commands such as #else. That inconsistency turns out to have been self-inflicted damage from a poorly-thought-through post-indent "fixup" in pgindent. This patch is much less interesting than the first round of indent changes, but also bulkier, so I thought it best to separate the effects. Discussion: https://postgr.es/m/E1dAmxK-0006EE-1r@gemulon.postgresql.org Discussion: https://postgr.es/m/30527.1495162840@sss.pgh.pa.us
2017-06-21 21:18:54 +02:00
phinfo->ph_lateral = NULL; /* make it exactly NULL if empty */
Fix planner problems with LATERAL references in PlaceHolderVars. The planner largely failed to consider the possibility that a PlaceHolderVar's expression might contain a lateral reference to a Var coming from somewhere outside the PHV's syntactic scope. We had a previous report of a problem in this area, which I tried to fix in a quick-hack way in commit 4da6439bd8553059766011e2a42c6e39df08717f, but Antonin Houska pointed out that there were still some problems, and investigation turned up other issues. This patch largely reverts that commit in favor of a more thoroughly thought-through solution. The new theory is that a PHV's ph_eval_at level cannot be higher than its original syntactic level. If it contains lateral references, those don't change the ph_eval_at level, but rather they create a lateral-reference requirement for the ph_eval_at join relation. The code in joinpath.c needs to handle that. Another issue is that createplan.c wasn't handling nested PlaceHolderVars properly. In passing, push knowledge of lateral-reference checks for join clauses into join_clause_is_movable_to. This is mainly so that FDWs don't need to deal with it. This patch doesn't fix the original join-qual-placement problem reported by Jeremy Evans (and indeed, one of the new regression test cases shows the wrong answer because of that). But the PlaceHolderVar problems need to be fixed before that issue can be addressed, so committing this separately seems reasonable.
2013-08-18 02:22:37 +02:00
phinfo->ph_eval_at = bms_int_members(rels_used, phv->phrels);
/* If no contained vars, force evaluation at syntactic location */
if (bms_is_empty(phinfo->ph_eval_at))
{
phinfo->ph_eval_at = bms_copy(phv->phrels);
Assert(!bms_is_empty(phinfo->ph_eval_at));
}
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
/* ph_eval_at may change later, see update_placeholder_eval_levels */
8.4 pgindent run, with new combined Linux/FreeBSD/MinGW typedef list provided by Andrew.
2009-06-11 16:49:15 +02:00
phinfo->ph_needed = NULL; /* initially it's unused */
Dept of better ideas: refrain from creating the planner's placeholder_list until vars are distributed to rels during query_planner() startup. We don't really need it before that, and not building it early has some advantages. First, we don't need to put it through the various preprocessing steps, which saves some cycles and eliminates the need for a number of routines to support PlaceHolderInfo nodes at all. Second, this means one less unused plan for any sub-SELECT appearing in a placeholder's expression, since we don't build placeholder_list until after sublink expansion is complete.
2008-10-22 22:17:52 +02:00
/* for the moment, estimate width using just the datatype info */
phinfo->ph_width = get_typavgwidth(exprType((Node *) phv->phexpr),
exprTypmod((Node *) phv->phexpr));
root->placeholder_list = lappend(root->placeholder_list, phinfo);
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
/*
* The PHV's contained expression may contain other, lower-level PHVs. We
* now know we need to get those into the PlaceHolderInfo list, too, so we
* may as well do that immediately.
*/
find_placeholders_in_expr(root, (Node *) phinfo->ph_var->phexpr);
Dept of better ideas: refrain from creating the planner's placeholder_list until vars are distributed to rels during query_planner() startup. We don't really need it before that, and not building it early has some advantages. First, we don't need to put it through the various preprocessing steps, which saves some cycles and eliminates the need for a number of routines to support PlaceHolderInfo nodes at all. Second, this means one less unused plan for any sub-SELECT appearing in a placeholder's expression, since we don't build placeholder_list until after sublink expansion is complete.
2008-10-22 22:17:52 +02:00
return phinfo;
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
}
/*
Revisit handling of UNION ALL subqueries with non-Var output columns. In commit 57664ed25e5dea117158a2e663c29e60b3546e1c I tried to fix a bug reported by Teodor Sigaev by making non-simple-Var output columns distinct (by wrapping their expressions with dummy PlaceHolderVar nodes). This did not work too well. Commit b28ffd0fcc583c1811e5295279e7d4366c3cae6c fixed some ensuing problems with matching to child indexes, but per a recent report from Claus Stadler, constraint exclusion of UNION ALL subqueries was still broken, because constant-simplification didn't handle the injected PlaceHolderVars well either. On reflection, the original patch was quite misguided: there is no reason to expect that EquivalenceClass child members will be distinct. So instead of trying to make them so, we should ensure that we can cope with the situation when they're not. Accordingly, this patch reverts the code changes in the above-mentioned commits (though the regression test cases they added stay). Instead, I've added assorted defenses to make sure that duplicate EC child members don't cause any problems. Teodor's original problem ("MergeAppend child's targetlist doesn't match MergeAppend") is addressed more directly by revising prepare_sort_from_pathkeys to let the parent MergeAppend's sort list guide creation of each child's sort list. In passing, get rid of add_sort_column; as far as I can tell, testing for duplicate sort keys at this stage is dead code. Certainly it doesn't trigger often enough to be worth expending cycles on in ordinary queries. And keeping the test would've greatly complicated the new logic in prepare_sort_from_pathkeys, because comparing pathkey list entries against a previous output array requires that we not skip any entries in the list. Back-patch to 9.1, like the previous patches. The only known issue in this area that wasn't caused by the ill-advised previous patches was the MergeAppend planning failure, which of course is not relevant before 9.1. It's possible that we need some of the new defenses against duplicate child EC entries in older branches, but until there's some clear evidence of that I'm going to refrain from back-patching further.
2012-03-16 18:11:12 +01:00
* find_placeholders_in_jointree
* Search the jointree for PlaceHolderVars, and build PlaceHolderInfos
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
*
Revisit handling of UNION ALL subqueries with non-Var output columns. In commit 57664ed25e5dea117158a2e663c29e60b3546e1c I tried to fix a bug reported by Teodor Sigaev by making non-simple-Var output columns distinct (by wrapping their expressions with dummy PlaceHolderVar nodes). This did not work too well. Commit b28ffd0fcc583c1811e5295279e7d4366c3cae6c fixed some ensuing problems with matching to child indexes, but per a recent report from Claus Stadler, constraint exclusion of UNION ALL subqueries was still broken, because constant-simplification didn't handle the injected PlaceHolderVars well either. On reflection, the original patch was quite misguided: there is no reason to expect that EquivalenceClass child members will be distinct. So instead of trying to make them so, we should ensure that we can cope with the situation when they're not. Accordingly, this patch reverts the code changes in the above-mentioned commits (though the regression test cases they added stay). Instead, I've added assorted defenses to make sure that duplicate EC child members don't cause any problems. Teodor's original problem ("MergeAppend child's targetlist doesn't match MergeAppend") is addressed more directly by revising prepare_sort_from_pathkeys to let the parent MergeAppend's sort list guide creation of each child's sort list. In passing, get rid of add_sort_column; as far as I can tell, testing for duplicate sort keys at this stage is dead code. Certainly it doesn't trigger often enough to be worth expending cycles on in ordinary queries. And keeping the test would've greatly complicated the new logic in prepare_sort_from_pathkeys, because comparing pathkey list entries against a previous output array requires that we not skip any entries in the list. Back-patch to 9.1, like the previous patches. The only known issue in this area that wasn't caused by the ill-advised previous patches was the MergeAppend planning failure, which of course is not relevant before 9.1. It's possible that we need some of the new defenses against duplicate child EC entries in older branches, but until there's some clear evidence of that I'm going to refrain from back-patching further.
2012-03-16 18:11:12 +01:00
* We don't need to look at the targetlist because build_base_rel_tlists()
* will already have made entries for any PHVs in the tlist.
Fix planner problems with LATERAL references in PlaceHolderVars. The planner largely failed to consider the possibility that a PlaceHolderVar's expression might contain a lateral reference to a Var coming from somewhere outside the PHV's syntactic scope. We had a previous report of a problem in this area, which I tried to fix in a quick-hack way in commit 4da6439bd8553059766011e2a42c6e39df08717f, but Antonin Houska pointed out that there were still some problems, and investigation turned up other issues. This patch largely reverts that commit in favor of a more thoroughly thought-through solution. The new theory is that a PHV's ph_eval_at level cannot be higher than its original syntactic level. If it contains lateral references, those don't change the ph_eval_at level, but rather they create a lateral-reference requirement for the ph_eval_at join relation. The code in joinpath.c needs to handle that. Another issue is that createplan.c wasn't handling nested PlaceHolderVars properly. In passing, push knowledge of lateral-reference checks for join clauses into join_clause_is_movable_to. This is mainly so that FDWs don't need to deal with it. This patch doesn't fix the original join-qual-placement problem reported by Jeremy Evans (and indeed, one of the new regression test cases shows the wrong answer because of that). But the PlaceHolderVar problems need to be fixed before that issue can be addressed, so committing this separately seems reasonable.
2013-08-18 02:22:37 +02:00
*
* This is called before we begin deconstruct_jointree. Once we begin
* deconstruct_jointree, all active placeholders must be present in
* root->placeholder_list, because make_outerjoininfo and
* update_placeholder_eval_levels require this info to be available
* while we crawl up the join tree.
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
*/
void
Revisit handling of UNION ALL subqueries with non-Var output columns. In commit 57664ed25e5dea117158a2e663c29e60b3546e1c I tried to fix a bug reported by Teodor Sigaev by making non-simple-Var output columns distinct (by wrapping their expressions with dummy PlaceHolderVar nodes). This did not work too well. Commit b28ffd0fcc583c1811e5295279e7d4366c3cae6c fixed some ensuing problems with matching to child indexes, but per a recent report from Claus Stadler, constraint exclusion of UNION ALL subqueries was still broken, because constant-simplification didn't handle the injected PlaceHolderVars well either. On reflection, the original patch was quite misguided: there is no reason to expect that EquivalenceClass child members will be distinct. So instead of trying to make them so, we should ensure that we can cope with the situation when they're not. Accordingly, this patch reverts the code changes in the above-mentioned commits (though the regression test cases they added stay). Instead, I've added assorted defenses to make sure that duplicate EC child members don't cause any problems. Teodor's original problem ("MergeAppend child's targetlist doesn't match MergeAppend") is addressed more directly by revising prepare_sort_from_pathkeys to let the parent MergeAppend's sort list guide creation of each child's sort list. In passing, get rid of add_sort_column; as far as I can tell, testing for duplicate sort keys at this stage is dead code. Certainly it doesn't trigger often enough to be worth expending cycles on in ordinary queries. And keeping the test would've greatly complicated the new logic in prepare_sort_from_pathkeys, because comparing pathkey list entries against a previous output array requires that we not skip any entries in the list. Back-patch to 9.1, like the previous patches. The only known issue in this area that wasn't caused by the ill-advised previous patches was the MergeAppend planning failure, which of course is not relevant before 9.1. It's possible that we need some of the new defenses against duplicate child EC entries in older branches, but until there's some clear evidence of that I'm going to refrain from back-patching further.
2012-03-16 18:11:12 +01:00
find_placeholders_in_jointree(PlannerInfo *root)
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
{
/* We need do nothing if the query contains no PlaceHolderVars */
if (root->glob->lastPHId != 0)
{
Revisit handling of UNION ALL subqueries with non-Var output columns. In commit 57664ed25e5dea117158a2e663c29e60b3546e1c I tried to fix a bug reported by Teodor Sigaev by making non-simple-Var output columns distinct (by wrapping their expressions with dummy PlaceHolderVar nodes). This did not work too well. Commit b28ffd0fcc583c1811e5295279e7d4366c3cae6c fixed some ensuing problems with matching to child indexes, but per a recent report from Claus Stadler, constraint exclusion of UNION ALL subqueries was still broken, because constant-simplification didn't handle the injected PlaceHolderVars well either. On reflection, the original patch was quite misguided: there is no reason to expect that EquivalenceClass child members will be distinct. So instead of trying to make them so, we should ensure that we can cope with the situation when they're not. Accordingly, this patch reverts the code changes in the above-mentioned commits (though the regression test cases they added stay). Instead, I've added assorted defenses to make sure that duplicate EC child members don't cause any problems. Teodor's original problem ("MergeAppend child's targetlist doesn't match MergeAppend") is addressed more directly by revising prepare_sort_from_pathkeys to let the parent MergeAppend's sort list guide creation of each child's sort list. In passing, get rid of add_sort_column; as far as I can tell, testing for duplicate sort keys at this stage is dead code. Certainly it doesn't trigger often enough to be worth expending cycles on in ordinary queries. And keeping the test would've greatly complicated the new logic in prepare_sort_from_pathkeys, because comparing pathkey list entries against a previous output array requires that we not skip any entries in the list. Back-patch to 9.1, like the previous patches. The only known issue in this area that wasn't caused by the ill-advised previous patches was the MergeAppend planning failure, which of course is not relevant before 9.1. It's possible that we need some of the new defenses against duplicate child EC entries in older branches, but until there's some clear evidence of that I'm going to refrain from back-patching further.
2012-03-16 18:11:12 +01:00
/* Start recursion at top of jointree */
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
Assert(root->parse->jointree != NULL &&
IsA(root->parse->jointree, FromExpr));
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
find_placeholders_recurse(root, (Node *) root->parse->jointree);
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
}
}
/*
* find_placeholders_recurse
Revisit handling of UNION ALL subqueries with non-Var output columns. In commit 57664ed25e5dea117158a2e663c29e60b3546e1c I tried to fix a bug reported by Teodor Sigaev by making non-simple-Var output columns distinct (by wrapping their expressions with dummy PlaceHolderVar nodes). This did not work too well. Commit b28ffd0fcc583c1811e5295279e7d4366c3cae6c fixed some ensuing problems with matching to child indexes, but per a recent report from Claus Stadler, constraint exclusion of UNION ALL subqueries was still broken, because constant-simplification didn't handle the injected PlaceHolderVars well either. On reflection, the original patch was quite misguided: there is no reason to expect that EquivalenceClass child members will be distinct. So instead of trying to make them so, we should ensure that we can cope with the situation when they're not. Accordingly, this patch reverts the code changes in the above-mentioned commits (though the regression test cases they added stay). Instead, I've added assorted defenses to make sure that duplicate EC child members don't cause any problems. Teodor's original problem ("MergeAppend child's targetlist doesn't match MergeAppend") is addressed more directly by revising prepare_sort_from_pathkeys to let the parent MergeAppend's sort list guide creation of each child's sort list. In passing, get rid of add_sort_column; as far as I can tell, testing for duplicate sort keys at this stage is dead code. Certainly it doesn't trigger often enough to be worth expending cycles on in ordinary queries. And keeping the test would've greatly complicated the new logic in prepare_sort_from_pathkeys, because comparing pathkey list entries against a previous output array requires that we not skip any entries in the list. Back-patch to 9.1, like the previous patches. The only known issue in this area that wasn't caused by the ill-advised previous patches was the MergeAppend planning failure, which of course is not relevant before 9.1. It's possible that we need some of the new defenses against duplicate child EC entries in older branches, but until there's some clear evidence of that I'm going to refrain from back-patching further.
2012-03-16 18:11:12 +01:00
* One recursion level of find_placeholders_in_jointree.
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
*
* jtnode is the current jointree node to examine.
*/
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
static void
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
find_placeholders_recurse(PlannerInfo *root, Node *jtnode)
{
if (jtnode == NULL)
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
return;
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
if (IsA(jtnode, RangeTblRef))
{
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
/* No quals to deal with here */
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
}
else if (IsA(jtnode, FromExpr))
{
FromExpr *f = (FromExpr *) jtnode;
ListCell *l;
/*
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
* First, recurse to handle child joins.
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
*/
foreach(l, f->fromlist)
{
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
find_placeholders_recurse(root, lfirst(l));
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
}
/*
* Now process the top-level quals.
*/
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
find_placeholders_in_expr(root, f->quals);
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
}
else if (IsA(jtnode, JoinExpr))
{
JoinExpr *j = (JoinExpr *) jtnode;
/*
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
* First, recurse to handle child joins.
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
*/
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
find_placeholders_recurse(root, j->larg);
find_placeholders_recurse(root, j->rarg);
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
/* Process the qual clauses */
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
find_placeholders_in_expr(root, j->quals);
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
}
else
elog(ERROR, "unrecognized node type: %d",
(int) nodeTag(jtnode));
}
/*
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
* find_placeholders_in_expr
* Find all PlaceHolderVars in the given expression, and create
* PlaceHolderInfo entries for them.
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
*/
static void
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
find_placeholders_in_expr(PlannerInfo *root, Node *expr)
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
{
List *vars;
ListCell *vl;
/*
* pull_var_clause does more than we need here, but it'll do and it's
* convenient to use.
*/
Fix nested PlaceHolderVar expressions that appear only in targetlists. A PlaceHolderVar's expression might contain another, lower-level PlaceHolderVar. If the outer PlaceHolderVar is used, the inner one certainly will be also, and so we have to make sure that both of them get into the placeholder_list with correct ph_may_need values during the initial pre-scan of the query (before deconstruct_jointree starts). We did this correctly for PlaceHolderVars appearing in the query quals, but overlooked the issue for those appearing in the top-level targetlist; with the result that nested placeholders referenced only in the targetlist did not work correctly, as illustrated in bug #6154. While at it, add some error checking to find_placeholder_info to ensure that we don't try to create new placeholders after it's too late to do so; they have to all be created before deconstruct_jointree starts. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2011-08-09 06:48:51 +02:00
vars = pull_var_clause(expr,
Refactor pull_var_clause's API to make it less tedious to extend. In commit 1d97c19a0f748e94 and later c1d9579dd8bf3c92, we extended pull_var_clause's API by adding enum-type arguments. That's sort of a pain to maintain, though, because it means every time we add a new behavior we must touch every last one of the call sites, even if there's a reasonable default behavior that most of them could use. Let's switch over to using a bitmask of flags, instead; that seems more maintainable and might save a nanosecond or two as well. This commit changes no behavior in itself, though I'm going to follow it up with one that does add a new behavior. In passing, remove flatten_tlist(), which has not been used since 9.1 and would otherwise need the same API changes. Removing these enums means that optimizer/tlist.h no longer needs to depend on optimizer/var.h. Changing that caused a number of C files to need addition of #include "optimizer/var.h" (probably we can thank old runs of pgrminclude for that); but on balance it seems like a good change anyway.
2016-03-10 21:52:58 +01:00
PVC_RECURSE_AGGREGATES |
Give pull_var_clause() reject/recurse/return behavior for WindowFuncs too. All along, this function should have treated WindowFuncs in a manner similar to Aggrefs, ie with an option whether or not to recurse into them. By not considering the case, it was always recursing, which is OK for most callers (although I suspect that the case in prepare_sort_from_pathkeys might represent a bug). But now we need return-without-recursing behavior as well. There are also more than a few callers that should never see a WindowFunc, and now we'll get some error checking on that.
2016-03-10 22:23:40 +01:00
PVC_RECURSE_WINDOWFUNCS |
Avoid listing ungrouped Vars in the targetlist of Agg-underneath-Window. Regular aggregate functions in combination with, or within the arguments of, window functions are OK per spec; they have the semantics that the aggregate output rows are computed and then we run the window functions over that row set. (Thus, this combination is not really useful unless there's a GROUP BY so that more than one aggregate output row is possible.) The case without GROUP BY could fail, as recently reported by Jeff Davis, because sloppy construction of the Agg node's targetlist resulted in extra references to possibly-ungrouped Vars appearing outside the aggregate function calls themselves. See the added regression test case for an example. Fixing this requires modifying the API of flatten_tlist and its underlying function pull_var_clause. I chose to make pull_var_clause's API for aggregates identical to what it was already doing for placeholders, since the useful behaviors turn out to be the same (error, report node as-is, or recurse into it). I also tightened the error checking in this area a bit: if it was ever valid to see an uplevel Var, Aggref, or PlaceHolderVar here, that was a long time ago, so complain instead of ignoring them. Backpatch into 9.1. The failure exists in 8.4 and 9.0 as well, but seeing that it only occurs in a basically-useless corner case, it doesn't seem worth the risks of changing a function API in a minor release. There might be third-party code using pull_var_clause.
2011-07-13 00:23:55 +02:00
PVC_INCLUDE_PLACEHOLDERS);
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
foreach(vl, vars)
{
PlaceHolderVar *phv = (PlaceHolderVar *) lfirst(vl);
/* Ignore any plain Vars */
if (!IsA(phv, PlaceHolderVar))
continue;
/* Create a PlaceHolderInfo entry if there's not one already */
Remove ph_may_need from PlaceHolderInfo, with attendant simplifications. The planner logic that attempted to make a preliminary estimate of the ph_needed levels for PlaceHolderVars seems to be completely broken by lateral references. Fortunately, the potential join order optimization that this code supported seems to be of relatively little value in practice; so let's just get rid of it rather than trying to fix it. Getting rid of this allows fairly substantial simplifications in placeholder.c, too, so planning in such cases should be a bit faster. Issue noted while pursuing bugs reported by Jeremy Evans and Antonin Houska, though this doesn't in itself fix either of their reported cases. What this does do is prevent an Assert crash in the kind of query illustrated by the added regression test. (I'm not sure that the plan for that query is stable enough across platforms to be usable as a regression test output ... but we'll soon find out from the buildfarm.) Back-patch to 9.3. The problem case can't arise without LATERAL, so no need to touch older branches.
2013-08-15 00:38:32 +02:00
(void) find_placeholder_info(root, phv, true);
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
}
list_free(vars);
}
/*
* update_placeholder_eval_levels
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
* Adjust the target evaluation levels for placeholders
*
Dept of better ideas: refrain from creating the planner's placeholder_list until vars are distributed to rels during query_planner() startup. We don't really need it before that, and not building it early has some advantages. First, we don't need to put it through the various preprocessing steps, which saves some cycles and eliminates the need for a number of routines to support PlaceHolderInfo nodes at all. Second, this means one less unused plan for any sub-SELECT appearing in a placeholder's expression, since we don't build placeholder_list until after sublink expansion is complete.
2008-10-22 22:17:52 +02:00
* The initial eval_at level set by find_placeholder_info was the set of
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
* rels used in the placeholder's expression (or the whole subselect below
* the placeholder's syntactic location, if the expr is variable-free).
Fix planner problems with LATERAL references in PlaceHolderVars. The planner largely failed to consider the possibility that a PlaceHolderVar's expression might contain a lateral reference to a Var coming from somewhere outside the PHV's syntactic scope. We had a previous report of a problem in this area, which I tried to fix in a quick-hack way in commit 4da6439bd8553059766011e2a42c6e39df08717f, but Antonin Houska pointed out that there were still some problems, and investigation turned up other issues. This patch largely reverts that commit in favor of a more thoroughly thought-through solution. The new theory is that a PHV's ph_eval_at level cannot be higher than its original syntactic level. If it contains lateral references, those don't change the ph_eval_at level, but rather they create a lateral-reference requirement for the ph_eval_at join relation. The code in joinpath.c needs to handle that. Another issue is that createplan.c wasn't handling nested PlaceHolderVars properly. In passing, push knowledge of lateral-reference checks for join clauses into join_clause_is_movable_to. This is mainly so that FDWs don't need to deal with it. This patch doesn't fix the original join-qual-placement problem reported by Jeremy Evans (and indeed, one of the new regression test cases shows the wrong answer because of that). But the PlaceHolderVar problems need to be fixed before that issue can be addressed, so committing this separately seems reasonable.
2013-08-18 02:22:37 +02:00
* If the query contains any outer joins that can null any of those rels,
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
* we must delay evaluation to above those joins.
*
* We repeat this operation each time we add another outer join to
* root->join_info_list. It's somewhat annoying to have to do that, but
* since we don't have very much information on the placeholders' locations,
* it's hard to avoid. Each placeholder's eval_at level must be correct
* by the time it starts to figure in outer-join delay decisions for higher
* outer joins.
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
*
* In future we might want to put additional policy/heuristics here to
* try to determine an optimal evaluation level. The current rules will
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
* result in evaluation at the lowest possible level. However, pushing a
* placeholder eval up the tree is likely to further constrain evaluation
* order for outer joins, so it could easily be counterproductive; and we
* don't have enough information at this point to make an intelligent choice.
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
*/
void
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
update_placeholder_eval_levels(PlannerInfo *root, SpecialJoinInfo *new_sjinfo)
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
{
ListCell *lc1;
foreach(lc1, root->placeholder_list)
{
PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc1);
Relids syn_level = phinfo->ph_var->phrels;
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
Relids eval_at;
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
bool found_some;
ListCell *lc2;
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
/*
* We don't need to do any work on this placeholder unless the
* newly-added outer join is syntactically beneath its location.
*/
if (!bms_is_subset(new_sjinfo->syn_lefthand, syn_level) ||
!bms_is_subset(new_sjinfo->syn_righthand, syn_level))
continue;
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
/*
* Check for delays due to lower outer joins. This is the same logic
* as in check_outerjoin_delay in initsplan.c, except that we don't
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
* have anything to do with the delay_upper_joins flags; delay of
* upper outer joins will be handled later, based on the eval_at
* values we compute now.
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
*/
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
eval_at = phinfo->ph_eval_at;
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
do
{
found_some = false;
foreach(lc2, root->join_info_list)
{
SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc2);
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
/* disregard joins not within the PHV's sub-select */
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
if (!bms_is_subset(sjinfo->syn_lefthand, syn_level) ||
!bms_is_subset(sjinfo->syn_righthand, syn_level))
continue;
/* do we reference any nullable rels of this OJ? */
if (bms_overlap(eval_at, sjinfo->min_righthand) ||
(sjinfo->jointype == JOIN_FULL &&
bms_overlap(eval_at, sjinfo->min_lefthand)))
{
/* yes; have we included all its rels in eval_at? */
if (!bms_is_subset(sjinfo->min_lefthand, eval_at) ||
!bms_is_subset(sjinfo->min_righthand, eval_at))
{
/* no, so add them in */
eval_at = bms_add_members(eval_at,
sjinfo->min_lefthand);
eval_at = bms_add_members(eval_at,
sjinfo->min_righthand);
/* we'll need another iteration */
found_some = true;
}
}
}
} while (found_some);
Fix planner problems with LATERAL references in PlaceHolderVars. The planner largely failed to consider the possibility that a PlaceHolderVar's expression might contain a lateral reference to a Var coming from somewhere outside the PHV's syntactic scope. We had a previous report of a problem in this area, which I tried to fix in a quick-hack way in commit 4da6439bd8553059766011e2a42c6e39df08717f, but Antonin Houska pointed out that there were still some problems, and investigation turned up other issues. This patch largely reverts that commit in favor of a more thoroughly thought-through solution. The new theory is that a PHV's ph_eval_at level cannot be higher than its original syntactic level. If it contains lateral references, those don't change the ph_eval_at level, but rather they create a lateral-reference requirement for the ph_eval_at join relation. The code in joinpath.c needs to handle that. Another issue is that createplan.c wasn't handling nested PlaceHolderVars properly. In passing, push knowledge of lateral-reference checks for join clauses into join_clause_is_movable_to. This is mainly so that FDWs don't need to deal with it. This patch doesn't fix the original join-qual-placement problem reported by Jeremy Evans (and indeed, one of the new regression test cases shows the wrong answer because of that). But the PlaceHolderVar problems need to be fixed before that issue can be addressed, so committing this separately seems reasonable.
2013-08-18 02:22:37 +02:00
/* Can't move the PHV's eval_at level to above its syntactic level */
Assert(bms_is_subset(eval_at, syn_level));
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
phinfo->ph_eval_at = eval_at;
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
}
}
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
/*
* fix_placeholder_input_needed_levels
* Adjust the "needed at" levels for placeholder inputs
*
* This is called after we've finished determining the eval_at levels for
* all placeholders. We need to make sure that all vars and placeholders
Fix planner problems with LATERAL references in PlaceHolderVars. The planner largely failed to consider the possibility that a PlaceHolderVar's expression might contain a lateral reference to a Var coming from somewhere outside the PHV's syntactic scope. We had a previous report of a problem in this area, which I tried to fix in a quick-hack way in commit 4da6439bd8553059766011e2a42c6e39df08717f, but Antonin Houska pointed out that there were still some problems, and investigation turned up other issues. This patch largely reverts that commit in favor of a more thoroughly thought-through solution. The new theory is that a PHV's ph_eval_at level cannot be higher than its original syntactic level. If it contains lateral references, those don't change the ph_eval_at level, but rather they create a lateral-reference requirement for the ph_eval_at join relation. The code in joinpath.c needs to handle that. Another issue is that createplan.c wasn't handling nested PlaceHolderVars properly. In passing, push knowledge of lateral-reference checks for join clauses into join_clause_is_movable_to. This is mainly so that FDWs don't need to deal with it. This patch doesn't fix the original join-qual-placement problem reported by Jeremy Evans (and indeed, one of the new regression test cases shows the wrong answer because of that). But the PlaceHolderVar problems need to be fixed before that issue can be addressed, so committing this separately seems reasonable.
2013-08-18 02:22:37 +02:00
* needed to evaluate each placeholder will be available at the scan or join
* level where the evaluation will be done. (It might seem that scan-level
* evaluations aren't interesting, but that's not so: a LATERAL reference
* within a placeholder's expression needs to cause the referenced var or
* placeholder to be marked as needed in the scan where it's evaluated.)
* Note that this loop can have side-effects on the ph_needed sets of other
* PlaceHolderInfos; that's okay because we don't examine ph_needed here, so
* there are no ordering issues to worry about.
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
*/
void
fix_placeholder_input_needed_levels(PlannerInfo *root)
{
ListCell *lc;
foreach(lc, root->placeholder_list)
{
PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc);
Fix planner problems with LATERAL references in PlaceHolderVars. The planner largely failed to consider the possibility that a PlaceHolderVar's expression might contain a lateral reference to a Var coming from somewhere outside the PHV's syntactic scope. We had a previous report of a problem in this area, which I tried to fix in a quick-hack way in commit 4da6439bd8553059766011e2a42c6e39df08717f, but Antonin Houska pointed out that there were still some problems, and investigation turned up other issues. This patch largely reverts that commit in favor of a more thoroughly thought-through solution. The new theory is that a PHV's ph_eval_at level cannot be higher than its original syntactic level. If it contains lateral references, those don't change the ph_eval_at level, but rather they create a lateral-reference requirement for the ph_eval_at join relation. The code in joinpath.c needs to handle that. Another issue is that createplan.c wasn't handling nested PlaceHolderVars properly. In passing, push knowledge of lateral-reference checks for join clauses into join_clause_is_movable_to. This is mainly so that FDWs don't need to deal with it. This patch doesn't fix the original join-qual-placement problem reported by Jeremy Evans (and indeed, one of the new regression test cases shows the wrong answer because of that). But the PlaceHolderVar problems need to be fixed before that issue can be addressed, so committing this separately seems reasonable.
2013-08-18 02:22:37 +02:00
List *vars = pull_var_clause((Node *) phinfo->ph_var->phexpr,
Refactor pull_var_clause's API to make it less tedious to extend. In commit 1d97c19a0f748e94 and later c1d9579dd8bf3c92, we extended pull_var_clause's API by adding enum-type arguments. That's sort of a pain to maintain, though, because it means every time we add a new behavior we must touch every last one of the call sites, even if there's a reasonable default behavior that most of them could use. Let's switch over to using a bitmask of flags, instead; that seems more maintainable and might save a nanosecond or two as well. This commit changes no behavior in itself, though I'm going to follow it up with one that does add a new behavior. In passing, remove flatten_tlist(), which has not been used since 9.1 and would otherwise need the same API changes. Removing these enums means that optimizer/tlist.h no longer needs to depend on optimizer/var.h. Changing that caused a number of C files to need addition of #include "optimizer/var.h" (probably we can thank old runs of pgrminclude for that); but on balance it seems like a good change anyway.
2016-03-10 21:52:58 +01:00
PVC_RECURSE_AGGREGATES |
Give pull_var_clause() reject/recurse/return behavior for WindowFuncs too. All along, this function should have treated WindowFuncs in a manner similar to Aggrefs, ie with an option whether or not to recurse into them. By not considering the case, it was always recursing, which is OK for most callers (although I suspect that the case in prepare_sort_from_pathkeys might represent a bug). But now we need return-without-recursing behavior as well. There are also more than a few callers that should never see a WindowFunc, and now we'll get some error checking on that.
2016-03-10 22:23:40 +01:00
PVC_RECURSE_WINDOWFUNCS |
Fix planner problems with LATERAL references in PlaceHolderVars. The planner largely failed to consider the possibility that a PlaceHolderVar's expression might contain a lateral reference to a Var coming from somewhere outside the PHV's syntactic scope. We had a previous report of a problem in this area, which I tried to fix in a quick-hack way in commit 4da6439bd8553059766011e2a42c6e39df08717f, but Antonin Houska pointed out that there were still some problems, and investigation turned up other issues. This patch largely reverts that commit in favor of a more thoroughly thought-through solution. The new theory is that a PHV's ph_eval_at level cannot be higher than its original syntactic level. If it contains lateral references, those don't change the ph_eval_at level, but rather they create a lateral-reference requirement for the ph_eval_at join relation. The code in joinpath.c needs to handle that. Another issue is that createplan.c wasn't handling nested PlaceHolderVars properly. In passing, push knowledge of lateral-reference checks for join clauses into join_clause_is_movable_to. This is mainly so that FDWs don't need to deal with it. This patch doesn't fix the original join-qual-placement problem reported by Jeremy Evans (and indeed, one of the new regression test cases shows the wrong answer because of that). But the PlaceHolderVar problems need to be fixed before that issue can be addressed, so committing this separately seems reasonable.
2013-08-18 02:22:37 +02:00
PVC_INCLUDE_PLACEHOLDERS);
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
Fix planner problems with LATERAL references in PlaceHolderVars. The planner largely failed to consider the possibility that a PlaceHolderVar's expression might contain a lateral reference to a Var coming from somewhere outside the PHV's syntactic scope. We had a previous report of a problem in this area, which I tried to fix in a quick-hack way in commit 4da6439bd8553059766011e2a42c6e39df08717f, but Antonin Houska pointed out that there were still some problems, and investigation turned up other issues. This patch largely reverts that commit in favor of a more thoroughly thought-through solution. The new theory is that a PHV's ph_eval_at level cannot be higher than its original syntactic level. If it contains lateral references, those don't change the ph_eval_at level, but rather they create a lateral-reference requirement for the ph_eval_at join relation. The code in joinpath.c needs to handle that. Another issue is that createplan.c wasn't handling nested PlaceHolderVars properly. In passing, push knowledge of lateral-reference checks for join clauses into join_clause_is_movable_to. This is mainly so that FDWs don't need to deal with it. This patch doesn't fix the original join-qual-placement problem reported by Jeremy Evans (and indeed, one of the new regression test cases shows the wrong answer because of that). But the PlaceHolderVar problems need to be fixed before that issue can be addressed, so committing this separately seems reasonable.
2013-08-18 02:22:37 +02:00
add_vars_to_targetlist(root, vars, phinfo->ph_eval_at, false);
list_free(vars);
Dept of better ideas: refrain from creating the planner's placeholder_list until vars are distributed to rels during query_planner() startup. We don't really need it before that, and not building it early has some advantages. First, we don't need to put it through the various preprocessing steps, which saves some cycles and eliminates the need for a number of routines to support PlaceHolderInfo nodes at all. Second, this means one less unused plan for any sub-SELECT appearing in a placeholder's expression, since we don't build placeholder_list until after sublink expansion is complete.
2008-10-22 22:17:52 +02:00
}
Rework join-removal logic as per recent discussion. In particular this fixes things so that it works for cases where nested removals are possible. The overhead of the optimization should be significantly less, as well.
2010-03-29 00:59:34 +02:00
}
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
Rework join-removal logic as per recent discussion. In particular this fixes things so that it works for cases where nested removals are possible. The overhead of the optimization should be significantly less, as well.
2010-03-29 00:59:34 +02:00
/*
* add_placeholders_to_base_rels
Get rid of the planner's LateralJoinInfo data structure. I originally modeled this data structure on SpecialJoinInfo, but after commit acfcd45cacb6df23 that looks like a pretty poor decision. All we really need is relid sets identifying laterally-referenced rels; and most of the time, what we want to know about includes indirect lateral references, a case the LateralJoinInfo data was unsuited to compute with any efficiency. The previous commit redefined RelOptInfo.lateral_relids as the transitive closure of lateral references, so that it easily supports checking indirect references. For the places where we really do want just direct references, add a new RelOptInfo field direct_lateral_relids, which is easily set up as a copy of lateral_relids before we perform the transitive closure calculation. Then we can just drop lateral_info_list and LateralJoinInfo and the supporting code. This makes the planner's handling of lateral references noticeably more efficient, and shorter too. Such a change can't be back-patched into stable branches for fear of breaking extensions that might be looking at the planner's data structures; but it seems not too late to push it into 9.5, so I've done so.
2015-12-11 21:52:16 +01:00
* Add any required PlaceHolderVars to base rels' targetlists.
Rework join-removal logic as per recent discussion. In particular this fixes things so that it works for cases where nested removals are possible. The overhead of the optimization should be significantly less, as well.
2010-03-29 00:59:34 +02:00
*
* If any placeholder can be computed at a base rel and is needed above it,
Get rid of the planner's LateralJoinInfo data structure. I originally modeled this data structure on SpecialJoinInfo, but after commit acfcd45cacb6df23 that looks like a pretty poor decision. All we really need is relid sets identifying laterally-referenced rels; and most of the time, what we want to know about includes indirect lateral references, a case the LateralJoinInfo data was unsuited to compute with any efficiency. The previous commit redefined RelOptInfo.lateral_relids as the transitive closure of lateral references, so that it easily supports checking indirect references. For the places where we really do want just direct references, add a new RelOptInfo field direct_lateral_relids, which is easily set up as a copy of lateral_relids before we perform the transitive closure calculation. Then we can just drop lateral_info_list and LateralJoinInfo and the supporting code. This makes the planner's handling of lateral references noticeably more efficient, and shorter too. Such a change can't be back-patched into stable branches for fear of breaking extensions that might be looking at the planner's data structures; but it seems not too late to push it into 9.5, so I've done so.
2015-12-11 21:52:16 +01:00
* add it to that rel's targetlist. This might look like it could be merged
Fix PlaceHolderVar mechanism's interaction with outer joins. The point of a PlaceHolderVar is to allow a non-strict expression to be evaluated below an outer join, after which its value bubbles up like a Var and can be forced to NULL when the outer join's semantics require that. However, there was a serious design oversight in that, namely that we didn't ensure that there was actually a correct place in the plan tree to evaluate the placeholder :-(. It may be necessary to delay evaluation of an outer join to ensure that a placeholder that should be evaluated below the join can be evaluated there. Per recent bug report from Kirill Simonov. Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
2010-09-28 18:08:56 +02:00
* with fix_placeholder_input_needed_levels, but it must be separate because
* join removal happens in between, and can change the ph_eval_at sets. There
* is essentially the same logic in add_placeholders_to_joinrel, but we can't
* do that part until joinrels are formed.
Rework join-removal logic as per recent discussion. In particular this fixes things so that it works for cases where nested removals are possible. The overhead of the optimization should be significantly less, as well.
2010-03-29 00:59:34 +02:00
*/
void
add_placeholders_to_base_rels(PlannerInfo *root)
{
ListCell *lc;
foreach(lc, root->placeholder_list)
Dept of better ideas: refrain from creating the planner's placeholder_list until vars are distributed to rels during query_planner() startup. We don't really need it before that, and not building it early has some advantages. First, we don't need to put it through the various preprocessing steps, which saves some cycles and eliminates the need for a number of routines to support PlaceHolderInfo nodes at all. Second, this means one less unused plan for any sub-SELECT appearing in a placeholder's expression, since we don't build placeholder_list until after sublink expansion is complete.
2008-10-22 22:17:52 +02:00
{
Rework join-removal logic as per recent discussion. In particular this fixes things so that it works for cases where nested removals are possible. The overhead of the optimization should be significantly less, as well.
2010-03-29 00:59:34 +02:00
PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc);
Dept of better ideas: refrain from creating the planner's placeholder_list until vars are distributed to rels during query_planner() startup. We don't really need it before that, and not building it early has some advantages. First, we don't need to put it through the various preprocessing steps, which saves some cycles and eliminates the need for a number of routines to support PlaceHolderInfo nodes at all. Second, this means one less unused plan for any sub-SELECT appearing in a placeholder's expression, since we don't build placeholder_list until after sublink expansion is complete.
2008-10-22 22:17:52 +02:00
Relids eval_at = phinfo->ph_eval_at;
Add bms_get_singleton_member(), and use it where appropriate. This patch adds a function that replaces a bms_membership() test followed by a bms_singleton_member() call, performing both the test and the extraction of a singleton set's member in one scan of the bitmapset. The performance advantage over the old way is probably minimal in current usage, but it seems worthwhile on notational grounds anyway. David Rowley
2014-11-28 20:16:24 +01:00
int varno;
Dept of better ideas: refrain from creating the planner's placeholder_list until vars are distributed to rels during query_planner() startup. We don't really need it before that, and not building it early has some advantages. First, we don't need to put it through the various preprocessing steps, which saves some cycles and eliminates the need for a number of routines to support PlaceHolderInfo nodes at all. Second, this means one less unused plan for any sub-SELECT appearing in a placeholder's expression, since we don't build placeholder_list until after sublink expansion is complete.
2008-10-22 22:17:52 +02:00
Get rid of the planner's LateralJoinInfo data structure. I originally modeled this data structure on SpecialJoinInfo, but after commit acfcd45cacb6df23 that looks like a pretty poor decision. All we really need is relid sets identifying laterally-referenced rels; and most of the time, what we want to know about includes indirect lateral references, a case the LateralJoinInfo data was unsuited to compute with any efficiency. The previous commit redefined RelOptInfo.lateral_relids as the transitive closure of lateral references, so that it easily supports checking indirect references. For the places where we really do want just direct references, add a new RelOptInfo field direct_lateral_relids, which is easily set up as a copy of lateral_relids before we perform the transitive closure calculation. Then we can just drop lateral_info_list and LateralJoinInfo and the supporting code. This makes the planner's handling of lateral references noticeably more efficient, and shorter too. Such a change can't be back-patched into stable branches for fear of breaking extensions that might be looking at the planner's data structures; but it seems not too late to push it into 9.5, so I've done so.
2015-12-11 21:52:16 +01:00
if (bms_get_singleton_member(eval_at, &varno) &&
bms_nonempty_difference(phinfo->ph_needed, eval_at))
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
{
RelOptInfo *rel = find_base_rel(root, varno);
Rethink representation of PathTargets. In commit 19a541143a09c067 I did not make PathTarget a subtype of Node, and embedded a RelOptInfo's reltarget directly into it rather than having a separately-allocated Node. In hindsight that was misguided micro-optimization, enabled by the fact that at that point we didn't have any Paths with custom PathTargets. Now that PathTarget processing has been fleshed out some more, it's easier to see that it's better to have PathTarget as an indepedent Node type, even if it does cost us one more palloc to create a RelOptInfo. So change it while we still can. This commit just changes the representation, without doing anything more interesting than that.
2016-03-14 21:59:59 +01:00
rel->reltarget->exprs = lappend(rel->reltarget->exprs,
copyObject(phinfo->ph_var));
Add an explicit representation of the output targetlist to Paths. Up to now, there's been an assumption that all Paths for a given relation compute the same output column set (targetlist). However, there are good reasons to remove that assumption. For example, an indexscan on an expression index might be able to return the value of an expensive function "for free". While we have the ability to generate such a plan today in simple cases, we don't have a way to model that it's cheaper than a plan that computes the function from scratch, nor a way to create such a plan in join cases (where the function computation would normally happen at the topmost join node). Also, we need this so that we can have Paths representing post-scan/join steps, where the targetlist may well change from one step to the next. Therefore, invent a "struct PathTarget" representing the columns we expect a plan step to emit. It's convenient to include the output tuple width and tlist evaluation cost in this struct, and there will likely be additional fields in future. While Path nodes that actually do have custom outputs will need their own PathTargets, it will still be true that most Paths for a given relation will compute the same tlist. To reduce the overhead added by this patch, keep a "default PathTarget" in RelOptInfo, and allow Paths that compute that column set to just point to their parent RelOptInfo's reltarget. (In the patch as committed, actually every Path is like that, since we do not yet have any cases of custom PathTargets.) I took this opportunity to provide some more-honest costing of PlaceHolderVar evaluation. Up to now, the assumption that "scan/join reltargetlists have cost zero" was applied not only to Vars, where it's reasonable, but also PlaceHolderVars where it isn't. Now, we add the eval cost of a PlaceHolderVar's expression to the first plan level where it can be computed, by including it in the PathTarget cost field and adding that to the cost estimates for Paths. This isn't perfect yet but it's much better than before, and there is a way forward to improve it more. This costing change affects the join order chosen for a couple of the regression tests, changing expected row ordering.
2016-02-19 02:01:49 +01:00
/* reltarget's cost and width fields will be updated later */
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
}
}
}
/*
* add_placeholders_to_joinrel
Get rid of the planner's LateralJoinInfo data structure. I originally modeled this data structure on SpecialJoinInfo, but after commit acfcd45cacb6df23 that looks like a pretty poor decision. All we really need is relid sets identifying laterally-referenced rels; and most of the time, what we want to know about includes indirect lateral references, a case the LateralJoinInfo data was unsuited to compute with any efficiency. The previous commit redefined RelOptInfo.lateral_relids as the transitive closure of lateral references, so that it easily supports checking indirect references. For the places where we really do want just direct references, add a new RelOptInfo field direct_lateral_relids, which is easily set up as a copy of lateral_relids before we perform the transitive closure calculation. Then we can just drop lateral_info_list and LateralJoinInfo and the supporting code. This makes the planner's handling of lateral references noticeably more efficient, and shorter too. Such a change can't be back-patched into stable branches for fear of breaking extensions that might be looking at the planner's data structures; but it seems not too late to push it into 9.5, so I've done so.
2015-12-11 21:52:16 +01:00
* Add any required PlaceHolderVars to a join rel's targetlist;
* and if they contain lateral references, add those references to the
* joinrel's direct_lateral_relids.
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
*
* A join rel should emit a PlaceHolderVar if (a) the PHV is needed above
* this join level and (b) the PHV can be computed at or below this level.
*/
void
Add an explicit representation of the output targetlist to Paths. Up to now, there's been an assumption that all Paths for a given relation compute the same output column set (targetlist). However, there are good reasons to remove that assumption. For example, an indexscan on an expression index might be able to return the value of an expensive function "for free". While we have the ability to generate such a plan today in simple cases, we don't have a way to model that it's cheaper than a plan that computes the function from scratch, nor a way to create such a plan in join cases (where the function computation would normally happen at the topmost join node). Also, we need this so that we can have Paths representing post-scan/join steps, where the targetlist may well change from one step to the next. Therefore, invent a "struct PathTarget" representing the columns we expect a plan step to emit. It's convenient to include the output tuple width and tlist evaluation cost in this struct, and there will likely be additional fields in future. While Path nodes that actually do have custom outputs will need their own PathTargets, it will still be true that most Paths for a given relation will compute the same tlist. To reduce the overhead added by this patch, keep a "default PathTarget" in RelOptInfo, and allow Paths that compute that column set to just point to their parent RelOptInfo's reltarget. (In the patch as committed, actually every Path is like that, since we do not yet have any cases of custom PathTargets.) I took this opportunity to provide some more-honest costing of PlaceHolderVar evaluation. Up to now, the assumption that "scan/join reltargetlists have cost zero" was applied not only to Vars, where it's reasonable, but also PlaceHolderVars where it isn't. Now, we add the eval cost of a PlaceHolderVar's expression to the first plan level where it can be computed, by including it in the PathTarget cost field and adding that to the cost estimates for Paths. This isn't perfect yet but it's much better than before, and there is a way forward to improve it more. This costing change affects the join order chosen for a couple of the regression tests, changing expected row ordering.
2016-02-19 02:01:49 +01:00
add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
RelOptInfo *outer_rel, RelOptInfo *inner_rel)
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
{
Relids relids = joinrel->relids;
ListCell *lc;
foreach(lc, root->placeholder_list)
{
PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc);
/* Is it still needed above this joinrel? */
if (bms_nonempty_difference(phinfo->ph_needed, relids))
{
/* Is it computable here? */
if (bms_is_subset(phinfo->ph_eval_at, relids))
{
/* Yup, add it to the output */
Rethink representation of PathTargets. In commit 19a541143a09c067 I did not make PathTarget a subtype of Node, and embedded a RelOptInfo's reltarget directly into it rather than having a separately-allocated Node. In hindsight that was misguided micro-optimization, enabled by the fact that at that point we didn't have any Paths with custom PathTargets. Now that PathTarget processing has been fleshed out some more, it's easier to see that it's better to have PathTarget as an indepedent Node type, even if it does cost us one more palloc to create a RelOptInfo. So change it while we still can. This commit just changes the representation, without doing anything more interesting than that.
2016-03-14 21:59:59 +01:00
joinrel->reltarget->exprs = lappend(joinrel->reltarget->exprs,
phinfo->ph_var);
joinrel->reltarget->width += phinfo->ph_width;
Add an explicit representation of the output targetlist to Paths. Up to now, there's been an assumption that all Paths for a given relation compute the same output column set (targetlist). However, there are good reasons to remove that assumption. For example, an indexscan on an expression index might be able to return the value of an expensive function "for free". While we have the ability to generate such a plan today in simple cases, we don't have a way to model that it's cheaper than a plan that computes the function from scratch, nor a way to create such a plan in join cases (where the function computation would normally happen at the topmost join node). Also, we need this so that we can have Paths representing post-scan/join steps, where the targetlist may well change from one step to the next. Therefore, invent a "struct PathTarget" representing the columns we expect a plan step to emit. It's convenient to include the output tuple width and tlist evaluation cost in this struct, and there will likely be additional fields in future. While Path nodes that actually do have custom outputs will need their own PathTargets, it will still be true that most Paths for a given relation will compute the same tlist. To reduce the overhead added by this patch, keep a "default PathTarget" in RelOptInfo, and allow Paths that compute that column set to just point to their parent RelOptInfo's reltarget. (In the patch as committed, actually every Path is like that, since we do not yet have any cases of custom PathTargets.) I took this opportunity to provide some more-honest costing of PlaceHolderVar evaluation. Up to now, the assumption that "scan/join reltargetlists have cost zero" was applied not only to Vars, where it's reasonable, but also PlaceHolderVars where it isn't. Now, we add the eval cost of a PlaceHolderVar's expression to the first plan level where it can be computed, by including it in the PathTarget cost field and adding that to the cost estimates for Paths. This isn't perfect yet but it's much better than before, and there is a way forward to improve it more. This costing change affects the join order chosen for a couple of the regression tests, changing expected row ordering.
2016-02-19 02:01:49 +01:00
/*
* Charge the cost of evaluating the contained expression if
* the PHV can be computed here but not in either input. This
* is a bit bogus because we make the decision based on the
* first pair of possible input relations considered for the
* joinrel. With other pairs, it might be possible to compute
* the PHV in one input or the other, and then we'd be double
* charging the PHV's cost for some join paths. For now, live
* with that; but we might want to improve it later by
* refiguring the reltarget costs for each pair of inputs.
*/
if (!bms_is_subset(phinfo->ph_eval_at, outer_rel->relids) &&
!bms_is_subset(phinfo->ph_eval_at, inner_rel->relids))
{
QualCost cost;
cost_qual_eval_node(&cost, (Node *) phinfo->ph_var->phexpr,
root);
Rethink representation of PathTargets. In commit 19a541143a09c067 I did not make PathTarget a subtype of Node, and embedded a RelOptInfo's reltarget directly into it rather than having a separately-allocated Node. In hindsight that was misguided micro-optimization, enabled by the fact that at that point we didn't have any Paths with custom PathTargets. Now that PathTarget processing has been fleshed out some more, it's easier to see that it's better to have PathTarget as an indepedent Node type, even if it does cost us one more palloc to create a RelOptInfo. So change it while we still can. This commit just changes the representation, without doing anything more interesting than that.
2016-03-14 21:59:59 +01:00
joinrel->reltarget->cost.startup += cost.startup;
joinrel->reltarget->cost.per_tuple += cost.per_tuple;
Add an explicit representation of the output targetlist to Paths. Up to now, there's been an assumption that all Paths for a given relation compute the same output column set (targetlist). However, there are good reasons to remove that assumption. For example, an indexscan on an expression index might be able to return the value of an expensive function "for free". While we have the ability to generate such a plan today in simple cases, we don't have a way to model that it's cheaper than a plan that computes the function from scratch, nor a way to create such a plan in join cases (where the function computation would normally happen at the topmost join node). Also, we need this so that we can have Paths representing post-scan/join steps, where the targetlist may well change from one step to the next. Therefore, invent a "struct PathTarget" representing the columns we expect a plan step to emit. It's convenient to include the output tuple width and tlist evaluation cost in this struct, and there will likely be additional fields in future. While Path nodes that actually do have custom outputs will need their own PathTargets, it will still be true that most Paths for a given relation will compute the same tlist. To reduce the overhead added by this patch, keep a "default PathTarget" in RelOptInfo, and allow Paths that compute that column set to just point to their parent RelOptInfo's reltarget. (In the patch as committed, actually every Path is like that, since we do not yet have any cases of custom PathTargets.) I took this opportunity to provide some more-honest costing of PlaceHolderVar evaluation. Up to now, the assumption that "scan/join reltargetlists have cost zero" was applied not only to Vars, where it's reasonable, but also PlaceHolderVars where it isn't. Now, we add the eval cost of a PlaceHolderVar's expression to the first plan level where it can be computed, by including it in the PathTarget cost field and adding that to the cost estimates for Paths. This isn't perfect yet but it's much better than before, and there is a way forward to improve it more. This costing change affects the join order chosen for a couple of the regression tests, changing expected row ordering.
2016-02-19 02:01:49 +01:00
}
Get rid of the planner's LateralJoinInfo data structure. I originally modeled this data structure on SpecialJoinInfo, but after commit acfcd45cacb6df23 that looks like a pretty poor decision. All we really need is relid sets identifying laterally-referenced rels; and most of the time, what we want to know about includes indirect lateral references, a case the LateralJoinInfo data was unsuited to compute with any efficiency. The previous commit redefined RelOptInfo.lateral_relids as the transitive closure of lateral references, so that it easily supports checking indirect references. For the places where we really do want just direct references, add a new RelOptInfo field direct_lateral_relids, which is easily set up as a copy of lateral_relids before we perform the transitive closure calculation. Then we can just drop lateral_info_list and LateralJoinInfo and the supporting code. This makes the planner's handling of lateral references noticeably more efficient, and shorter too. Such a change can't be back-patched into stable branches for fear of breaking extensions that might be looking at the planner's data structures; but it seems not too late to push it into 9.5, so I've done so.
2015-12-11 21:52:16 +01:00
/* Adjust joinrel's direct_lateral_relids as needed */
joinrel->direct_lateral_relids =
bms_add_members(joinrel->direct_lateral_relids,
phinfo->ph_lateral);
Add a concept of "placeholder" variables to the planner. These are variables that represent some expression that we desire to compute below the top level of the plan, and then let that value "bubble up" as though it were a plain Var (ie, a column value). The immediate application is to allow sub-selects to be flattened even when they are below an outer join and have non-nullable output expressions. Formerly we couldn't flatten because such an expression wouldn't properly go to NULL when evaluated above the outer join. Now, we wrap it in a PlaceHolderVar and arrange for the actual evaluation to occur below the outer join. When the resulting Var bubbles up through the join, it will be set to NULL if necessary, yielding the correct results. This fixes a planner limitation that's existed since 7.1. In future we might want to use this mechanism to re-introduce some form of Hellerstein's "expensive functions" optimization, ie place the evaluation of an expensive function at the most suitable point in the plan tree.
2008-10-21 22:42:53 +02:00
}
}
}
}