We can remove a left join to a relation if the relation's output is
provably distinct for the columns involved in the join clause (considering
only equijoin clauses) and the relation supplies no variables needed above
the join. Previously, the join removal logic could only prove distinctness
by reference to unique indexes of a table. This patch extends the logic
to consider subquery relations, wherein distinctness might be proven by
reference to GROUP BY, DISTINCT, etc.
We actually already had some code to check that a subquery's output was
provably distinct, but it was hidden inside pathnode.c; which was a pretty
bad place for it really, since that file is mostly boilerplate Path
construction and comparison. Move that code to analyzejoins.c, which is
arguably a more appropriate location, and is certainly the site of the
new usage for it.
David Rowley, reviewed by Simon Riggs
Although this bug is already fixed in post-9.2 branches, the case
triggering it is quite different from what was under consideration
at the time. It seems worth memorializing this example in HEAD
just to make sure it doesn't get broken again in future.
Extracted from commit 187ae17300.
This reverts commit ee1e5662d8, as well as
a remarkably large number of followup commits, which were mostly concerned
with the fact that the implementation didn't work terribly well. It still
doesn't: we probably need some rather basic work in the GUC infrastructure
if we want to fully support GUCs whose default varies depending on the
value of another GUC. Meanwhile, it also emerged that there wasn't really
consensus in favor of the definition the patch tried to implement (ie,
effective_cache_size should default to 4 times shared_buffers). So whack
it all back to where it was. In a followup commit, I'll do what was
recently agreed to, which is to simply change the default to a higher
value.
When pulling a "postponed" qual from a LATERAL subquery up into the quals
of an outer join, we must make sure that the postponed qual is included
in those seen by make_outerjoininfo(). Otherwise we might compute a
too-small min_lefthand or min_righthand for the outer join, leading to
"JOIN qualification cannot refer to other relations" failures from
distribute_qual_to_rels. Subtler errors in the created plan seem possible,
too, if the extra qual would only affect join ordering constraints.
Per bug #9041 from David Leverton. Back-patch to 9.3.
On second thought, commit 0c051c9008 was
over-hasty: rather than allowing this case, we ought to reject it for now.
That leaves the field clear for a future feature that allows the target
table to be re-specified in the FROM (or USING) clause, which will enable
left-joining the target table to something else. We can then also allow
LATERAL references to such an explicitly re-specified target table.
But allowing them right now will create ambiguities or worse for such a
feature, and it isn't something we documented 9.3 as supporting.
While at it, add a convenience subroutine to avoid having several copies
of the ereport for disalllowed-LATERAL-reference cases.
I failed to think much about UPDATE/DELETE when implementing LATERAL :-(.
The implemented behavior ended up being that subqueries in the FROM or
USING clause (respectively) could access the update/delete target table as
though it were a lateral reference; which seems fine if they said LATERAL,
but certainly ought to draw an error if they didn't. Fix it so you get a
suitable error when you omit LATERAL. Per report from Emre Hasegeli.
It's possible to extract a restriction OR clause from a join clause that
has the form of an OR-of-ANDs, if each sub-AND includes a clause that
mentions only one specific relation. While PG has been aware of that idea
for many years, the code previously only did it if it could extract an
indexable OR clause. On reflection, though, that seems a silly limitation:
adding a restriction clause can be a win by reducing the number of rows
that have to be filtered at the join step, even if we have to test the
clause as a plain filter clause during the scan. This should be especially
useful for foreign tables, where the change can cut the number of rows that
have to be retrieved from the foreign server; but testing shows it can win
even on local tables. Per a suggestion from Robert Haas.
As a heuristic, I made the code accept an extracted restriction clause
if its estimated selectivity is less than 0.9, which will probably result
in accepting extracted clauses just about always. We might need to tweak
that later based on experience.
Since the code no longer has even a weak connection to Path creation,
remove orindxpath.c and create a new file optimizer/util/orclauses.c.
There's some additional janitorial cleanup of now-dead code that needs
to happen, but it seems like that's a fit subject for a separate commit.
Make the COPY test, which loads most of the large static tables used in
the tests, also explicitly ANALYZE those tables. This allows us to get
rid of various ad-hoc, and rather redundant, ANALYZE commands that had
gotten stuck into various test scripts over time to ensure we got
consistent plan choices. (We could have done a database-wide ANALYZE,
but that would cause stats to get attached to the small static tables
too, which results in plan changes compared to the historical behavior.
I'm not sure that's a good idea, so not going that far for now.)
Back-patch to 9.0, since 9.0 and 9.1 are currently sometimes failing
regression tests for lack of an "ANALYZE tenk1" in the subselect test.
There's no need for this in 8.4 since we didn't print any plans back
then.
pullup_replace_vars()'s decisions about whether a pulled-up replacement
expression needs to be wrapped in a PlaceHolderVar depend on the assumption
that what looks like a Var behaves like a Var. However, if the Var is a
join alias reference, later flattening of join aliases might replace the
Var with something that's not a Var at all, and should have been wrapped.
To fix, do a forcible pass of flatten_join_alias_vars() on the subquery
targetlist before we start to copy items out of it. We'll re-run that
processing on the pulled-up expressions later, but that's harmless.
Per report from Ken Tanzer; the added regression test case is based on his
example. This bug has been there since the PlaceHolderVar mechanism was
invented, but has escaped detection because the circumstances that trigger
it are fairly narrow. You need a flattenable query underneath an outer
join, which contains another flattenable query inside a join of its own,
with a dangerous expression (a constant or something else non-strict)
in that one's targetlist.
Having seen this, I'm wondering if it wouldn't be prudent to do all
alias-variable flattening earlier, perhaps even in the rewriter.
But that would probably not be a back-patchable change.
Bug #8591 from Claudio Freire demonstrates that get_eclass_for_sort_expr
must be able to compute valid em_nullable_relids for any new equivalence
class members it creates. I'd worried about this in the commit message
for db9f0e1d9a, but claimed that it wasn't a
problem because multi-member ECs should already exist when it runs. That
is transparently wrong, though, because this function is also called by
initialize_mergeclause_eclasses, which runs during deconstruct_jointree.
The example given in the bug report (which the new regression test item
is based upon) fails because the COALESCE() expression is first seen by
initialize_mergeclause_eclasses rather than process_equivalence.
Fixing this requires passing the appropriate nullable_relids set to
get_eclass_for_sort_expr, and it requires new code to compute that set
for top-level expressions such as ORDER BY, GROUP BY, etc. We store
the top-level nullable_relids in a new field in PlannerInfo to avoid
computing it many times. In the back branches, I've added the new
field at the end of the struct to minimize ABI breakage for planner
plugins. There doesn't seem to be a good alternative to changing
get_eclass_for_sort_expr's API signature, though. There probably aren't
any third-party extensions calling that function directly; moreover,
if there are, they probably need to think about what to pass for
nullable_relids anyway.
Back-patch to 9.2, like the previous patch in this area.
Although the SQL spec forbids duplicate table aliases, historically
we've allowed queries like
SELECT ... FROM tab1 x CROSS JOIN (tab2 x CROSS JOIN tab3 y) z
on the grounds that the aliased join (z) hides the aliases within it,
therefore there is no conflict between the two RTEs named "x". The
LATERAL patch broke this, on the misguided basis that "x" could be
ambiguous if tab3 were a LATERAL subquery. To avoid breaking existing
queries, it's better to allow this situation and complain only if
tab3 actually does contain an ambiguous reference. We need only remove
the check that was throwing an error, because the column lookup code
is already prepared to handle ambiguous references. Per bug #8444.
In an example such as
SELECT * FROM
i LEFT JOIN LATERAL (SELECT * FROM j WHERE i.n = j.n) j ON true;
it is safe to pull up the LATERAL subquery into its parent, but we must
then treat the "i.n = j.n" clause as a qual clause of the LEFT JOIN. The
previous coding in deconstruct_recurse mistakenly labeled the clause as
"is_pushed_down", resulting in wrong semantics if the clause were applied
at the join node, as per an example submitted awhile ago by Jeremy Evans.
To fix, postpone processing of such clauses until we return back up to
the appropriate recursion depth in deconstruct_recurse.
In addition, tighten the is-safe-to-pull-up checks in is_simple_subquery;
we previously missed the possibility that the LATERAL subquery might itself
contain an outer join that makes lateral references in lower quals unsafe.
A regression test case equivalent to Jeremy's example was already in my
commit of yesterday, but was giving the wrong results because of this
bug. This patch fixes the expected output for that, and also adds a
test case for the second problem.
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 4da6439bd8, 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.
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.
This patch gets rid of the concept of, and infrastructure for,
non-canonical PathKeys; we now only ever create canonical pathkey lists.
The need for non-canonical pathkeys came from the desire to have
grouping_planner initialize query_pathkeys and related pathkey lists before
calling query_planner. However, since query_planner didn't actually *do*
anything with those lists before they'd been made canonical, we can get rid
of the whole mess by just not creating the lists at all until the point
where we formerly canonicalized them.
There are several ways in which we could implement that without making
query_planner itself deal with grouping/sorting features (which are
supposed to be the province of grouping_planner). I chose to add a
callback function to query_planner's API; other alternatives would have
required adding more fields to PlannerInfo, which while not bad in itself
would create an ABI break for planner-related plugins in the 9.2 release
series. This still breaks ABI for anything that calls query_planner
directly, but it seems somewhat unlikely that there are any such plugins.
I had originally conceived of this change as merely a step on the way to
fixing bug #8049 from Teun Hoogendoorn; but it turns out that this fixes
that bug all by itself, as per the added regression test. The reason is
that now get_eclass_for_sort_expr is adding the ORDER BY expression at the
end of EquivalenceClass creation not the start, and so anything that is in
a multi-member EquivalenceClass has already been created with correct
em_nullable_relids. I am suspicious that there are related scenarios in
which we still need to teach get_eclass_for_sort_expr to compute correct
nullable_relids, but am not eager to risk destabilizing either 9.2 or 9.3
to fix bugs that are only hypothetical. So for the moment, do this and
stop here.
Back-patch to 9.2 but not to earlier branches, since they don't exhibit
this bug for lack of join-clause-movement logic that depends on
em_nullable_relids being correct. (We might have to revisit that choice
if any related bugs turn up.) In 9.2, don't change the signature of
make_pathkeys_for_sortclauses nor remove canonicalize_pathkeys, so as
not to risk more plugin breakage than we have to.
The SQL standard does not have general functions-in-FROM, but it does
allow UNNEST() there (see the <collection derived table> production),
and the semantics of that are defined to include lateral references.
So spec compliance requires allowing lateral references within UNNEST()
even without an explicit LATERAL keyword. Rather than making UNNEST()
a special case, it seems best to extend this flexibility to any
function-in-FROM. We'll still allow LATERAL to be written explicitly
for clarity's sake, but it's now a noise word in this context.
In theory this change could result in a change in behavior of existing
queries, by allowing what had been an outer reference in a function-in-FROM
to be captured by an earlier FROM-item at the same level. However, all
pre-9.3 PG releases have a bug that causes them to match variable
references to earlier FROM-items in preference to outer references (and
then throw an error). So no previously-working query could contain the
type of ambiguity that would risk a change of behavior.
Per a suggestion from Andrew Gierth, though I didn't use his patch.
If a potential equivalence clause references a variable from the nullable
side of an outer join, the planner needs to take care that derived clauses
are not pushed to below the outer join; else they may use the wrong value
for the variable. (The problem arises only with non-strict clauses, since
if an upper clause can be proven strict then the outer join will get
simplified to a plain join.) The planner attempted to prevent this type
of error by checking that potential equivalence clauses aren't
outerjoin-delayed as a whole, but actually we have to check each side
separately, since the two sides of the clause will get moved around
separately if it's treated as an equivalence. Bugs of this type can be
demonstrated as far back as 7.4, even though releases before 8.3 had only
a very ad-hoc notion of equivalence clauses.
In addition, we neglected to account for the possibility that such clauses
might have nonempty nullable_relids even when not outerjoin-delayed; so the
equivalence-class machinery lacked logic to compute correct nullable_relids
values for clauses it constructs. This oversight was harmless before 9.2
because we were only using RestrictInfo.nullable_relids for OR clauses;
but as of 9.2 it could result in pushing constructed equivalence clauses
to incorrect places. (This accounts for bug #7604 from Bill MacArthur.)
Fix the first problem by adding a new test check_equivalence_delay() in
distribute_qual_to_rels, and fix the second one by adding code in
equivclass.c and called functions to set correct nullable_relids for
generated clauses. Although I believe the second part of this is not
currently necessary before 9.2, I chose to back-patch it anyway, partly to
keep the logic similar across branches and partly because it seems possible
we might find other reasons why we need valid values of nullable_relids in
the older branches.
Add regression tests illustrating these problems. In 9.0 and up, also
add test cases checking that we can push constants through outer joins,
since we've broken that optimization before and I nearly broke it again
with an overly simplistic patch for this problem.
Some experimentation with examples similar to bug #7539 has convinced me
that indxpath.c's original implementation of parameterized-path generation
was several bricks shy of a load. In general, if we are relying on a
particular outer rel or set of outer rels for a parameterized path, the
path should use every indexable join clause that's available from that rel
or rels. Any join clauses that get left out of the indexqual will end up
getting applied as plain filter quals (qpquals), and that's generally a
significant loser compared to having the index AM enforce them. (This is
particularly true with btree, which can skip the index scan entirely if
it can see that the given indexquals are mutually contradictory.) The
original heuristics failed to ensure this, though, and were overly
complicated anyway. Rewrite to make the code explicitly identify each
useful set of outer rels and then select all applicable join clauses for
each one. The one plan that changes in the regression tests is in fact
for the better according to the planner's cost estimates.
(Note: this is not a correctness issue but just a matter of plan quality.
I don't yet know what is going on in bug #7539, but I don't expect this
change to fix that.)
We can detect whether the planner top level is going to care at all about
cheap startup cost (it will only do so if query_planner's tuple_fraction
argument is greater than zero). If it isn't, we might as well discard
paths immediately whose only advantage over others is cheap startup cost.
This turns out to get rid of quite a lot of paths in complex queries ---
I saw planner runtime reduction of more than a third on one large query.
Since add_path isn't currently passed the PlannerInfo "root", the easiest
way to tell it whether to do this was to add a bool flag to RelOptInfo.
That's a bit redundant, since all relations in a given query level will
have the same setting. But in the future it's possible that we'd refine
the control decision to work on a per-relation basis, so this seems like
a good arrangement anyway.
Per my suggestion of a few months ago.
If a PlaceHolderVar contains a pulled-up LATERAL reference, its minimum
possible evaluation level might be higher in the join tree than its
original syntactic location. That in turn affects the ph_needed level for
any contained PlaceHolderVars (that is, those PHVs had better propagate up
the join tree at least to the evaluation level of the outer PHV). We got
this mostly right, but mark_placeholder_maybe_needed() failed to account
for the effect, and in consequence could leave the inner PHVs with
ph_may_need less than what their ultimate ph_needed value will be. That's
bad because it could lead to failure to select a join order that will allow
evaluation of the inner PHV at a valid location. Fix that, and add an
Assert that checks that we don't ever set ph_needed to more than
ph_may_need.
This patch takes care of a number of problems having to do with failure
to choose valid join orders and incorrect handling of lateral references
pulled up from subqueries. Notable changes:
* Add a LateralJoinInfo data structure similar to SpecialJoinInfo, to
represent join ordering constraints created by lateral references.
(I first considered extending the SpecialJoinInfo structure, but the
semantics are different enough that a separate data structure seems
better.) Extend join_is_legal() and related functions to prevent trying
to form unworkable joins, and to ensure that we will consider joins that
satisfy lateral references even if the joins would be clauseless.
* Fill in the infrastructure needed for the last few types of relation scan
paths to support parameterization. We'd have wanted this eventually
anyway, but it is necessary now because a relation that gets pulled up out
of a UNION ALL subquery may acquire a reltargetlist containing lateral
references, meaning that its paths *have* to be parameterized whether or
not we have any code that can push join quals down into the scan.
* Compute data about lateral references early in query_planner(), and save
in RelOptInfo nodes, to avoid repetitive calculations later.
* Assorted corner-case bug fixes.
There's probably still some bugs left, but this is a lot closer to being
real than it was before.
Formerly, subquery pullup had no need to examine other entries in the range
table, since they could not contain any references to the subquery being
pulled up. That's no longer true with LATERAL, so now we need to be able
to visit rangetable subexpressions to replace Vars referencing the
pulled-up subquery. Also, this means that extract_lateral_references must
be unsurprised at encountering lateral PlaceHolderVars, since such might be
created when pulling up a subquery that's underneath an outer join with
respect to the lateral reference.
Re-allow subquery pullup for LATERAL subqueries, except when the subquery
is below an outer join and contains lateral references to relations outside
that outer join. If we pull up in such a case, we risk introducing lateral
cross-references into outer joins' ON quals, which is something the code is
entirely unprepared to cope with right now; and I'm not sure it'll ever be
worth coping with.
Support lateral refs in VALUES (this seems to be the only additional path
type that needs such support as a consequence of re-allowing subquery
pullup).
Put in a slightly hacky fix for joinpath.c's refusal to consider
parameterized join paths even when there cannot be any unparameterized
ones. This was causing "could not devise a query plan for the given query"
failures in queries involving more than two FROM items.
Put in an even more hacky fix for distribute_qual_to_rels() being unhappy
with join quals that contain references to rels outside their syntactic
scope; which is to say, disable that test altogether. Need to think about
how to preserve some sort of debugging cross-check here, while not
expending more cycles than befits a debugging cross-check.
The LATERAL marking has to be propagated down to the UNION leaf queries
when we pull them up. Also, fix the formerly stubbed-off
set_append_rel_pathlist(). It does already have enough smarts to cope with
making a parameterized Append path at need; it just has to not assume that
there *must* be an unparameterized path.
This patch implements the standard syntax of LATERAL attached to a
sub-SELECT in FROM, and also allows LATERAL attached to a function in FROM,
since set-returning function calls are expected to be one of the principal
use-cases.
The main change here is a rewrite of the mechanism for keeping track of
which relations are visible for column references while the FROM clause is
being scanned. The parser "namespace" lists are no longer lists of bare
RTEs, but are lists of ParseNamespaceItem structs, which carry an RTE
pointer as well as some visibility-controlling flags. Aside from
supporting LATERAL correctly, this lets us get rid of the ancient hacks
that required rechecking subqueries and JOIN/ON and function-in-FROM
expressions for invalid references after they were initially parsed.
Invalid column references are now always correctly detected on sight.
In passing, remove assorted parser error checks that are now dead code by
virtue of our having gotten rid of add_missing_from, as well as some
comments that are obsolete for the same reason. (It was mainly
add_missing_from that caused so much fudging here in the first place.)
The planner support for this feature is very minimal, and will be improved
in future patches. It works well enough for testing purposes, though.
catversion bump forced due to new field in RangeTblEntry.
This patch adjusts the treatment of parameterized paths so that all paths
with the same parameterization (same set of required outer rels) for the
same relation will have the same rowcount estimate. We cache the rowcount
estimates to ensure that property, and hopefully save a few cycles too.
Doing this makes it practical for add_path_precheck to operate without
a rowcount estimate: it need only assume that paths with different
parameterizations never dominate each other, which is close enough to
true anyway for coarse filtering, because normally a more-parameterized
path should yield fewer rows thanks to having more join clauses to apply.
In add_path, we do the full nine yards of comparing rowcount estimates
along with everything else, so that we can discard parameterized paths that
don't actually have an advantage. This fixes some issues I'd found with
add_path rejecting parameterized paths on the grounds that they were more
expensive than not-parameterized ones, even though they yielded many fewer
rows and hence would be cheaper once subsequent joining was considered.
To make the same-rowcounts assumption valid, we have to require that any
parameterized path enforce *all* join clauses that could be obtained from
the particular set of outer rels, even if not all of them are useful for
indexing. This is required at both base scans and joins. It's a good
thing anyway since the net impact is that join quals are checked at the
lowest practical level in the join tree. Hence, discard the original
rather ad-hoc mechanism for choosing parameterization joinquals, and build
a better one that has a more principled rule for when clauses can be moved.
The original rule was actually buggy anyway for lack of knowledge about
which relations are part of an outer join's outer side; getting this right
requires adding an outer_relids field to RestrictInfo.
We should be willing to cross-join two small relations if that allows us
to use an inner indexscan on a large relation (that is, the potential
indexqual for the large table requires both smaller relations). This
worked in simple cases but fell apart as soon as there was a join clause
to a fourth relation, because the existence of any two-relation join clause
caused the planner to not consider clauseless joins between other base
relations. The added regression test shows an example case adapted from
a recent complaint from Benoit Delbosc.
Adjust have_relevant_joinclause, have_relevant_eclass_joinclause, and
has_relevant_eclass_joinclause to consider that a join clause mentioning
three or more relations is sufficient grounds for joining any subset of
those relations, even if we have to do so via a cartesian join. Since such
clauses are relatively uncommon, this shouldn't affect planning speed on
typical queries; in fact it should help a bit, because the latter two
functions in particular get significantly simpler.
Although this is arguably a bug fix, I'm not going to risk back-patching
it, since it might have currently-unforeseen consequences.
For some reason, in the original coding of the PlaceHolderVar mechanism
I had supposed that PlaceHolderVars couldn't propagate into subqueries.
That is of course entirely possible. When it happens, we need to treat
an outer-level PlaceHolderVar much like an outer Var or Aggref, that is
SS_replace_correlation_vars() needs to replace the PlaceHolderVar with
a Param, and then when building the finished SubPlan we have to provide
the PlaceHolderVar expression as an actual parameter for the SubPlan.
The handling of the contained expression is a bit delicate but it can be
treated exactly like an Aggref's expression.
In addition to the missing logic in subselect.c, prepjointree.c was failing
to search subqueries for PlaceHolderVars that need their relids adjusted
during subquery pullup. It looks like everyplace else that touches
PlaceHolderVars got it right, though.
Per report from Mark Murawski. In 9.1 and HEAD, queries affected by this
oversight would fail with "ERROR: Upper-level PlaceHolderVar found where
not expected". But in 9.0 and 8.4, you'd silently get possibly-wrong
answers, since the value transmitted into the subquery wouldn't go to null
when it should.
If we use a PlaceHolderVar from the outer relation in an inner indexscan,
we need to reference the PlaceHolderVar as such as the value to be passed
in from the outer relation. The previous code effectively tried to
reconstruct the PHV from its component expression, which doesn't work since
(a) the Vars therein aren't necessarily bubbled up far enough, and (b) it
would be the wrong semantics anyway because of the possibility that the PHV
is supposed to have gone to null at some point before the current join.
Point (a) led to "variable not found in subplan target list" planner
errors, but point (b) would have led to silently wrong answers.
Per report from Roger Niederland.
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.
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.
The previous coding would decide that join removal was unsafe upon finding
a PlaceHolderVar that needed to be evaluated at the inner rel and then used
above the join. However, this fails to cover the case of PlaceHolderVars
that refer to both the inner rel and some other rels. Per bug report from
Andrus.
In these cases a qual can get marked with the removable rel in its
required_relids, but this is just to schedule its evaluation correctly, not
because it really depends on the rel. We were assuming that, in effect,
we could throw away *all* quals so marked, which is nonsense. Tighten up
the logic to be a little more paranoid about which quals belong to the
outer join being considered for removal, and arrange for all quals that
don't belong to be updated so they will still get evaluated correctly.
Also fix another problem that happened to be exposed by this test case,
which was that make_join_rel() was failing to notice some cases where
a constant-false qual could be used to prove a join relation empty. If it's
a pushed-down constant false, then the relation is empty even if it's an
outer join, because the qual applies after the outer join expansion.
Per report from Nathan Grange. Back-patch into 9.0.
peculiar variant of UNION ALL, and so wouldn't likely get written directly
as-is, it's possible for it to arise as a result of simplification of
less-obviously-silly queries. In particular, now that we can do flattening
of subqueries that have constant outputs and are underneath an outer join,
it's possible for the case to result from simplification of queries of the
type exhibited in bug #5263. Back-patch to 8.4 to avoid a functionality
regression for this type of query.
that's generated for a whole-row Var referencing the subquery, when the
subquery is in the nullable side of an outer join. The previous coding
instead put PlaceHolderVars around the elements of the RowExpr. The effect
was that when the outer join made the subquery outputs go to null, the
whole-row Var produced ROW(NULL,NULL,...) rather than just NULL. There
are arguments afoot about whether those things ought to be semantically
indistinguishable, but for the moment they are not entirely so, and the
planner needs to take care that its machinations preserve the difference.
Per bug #5025.
Making this feasible required refactoring ResolveNew() to allow more caller
control over what is substituted for a Var. I chose to make ResolveNew()
a wrapper around a new general-purpose function replace_rte_variables().
I also fixed the ancient bogosity that ResolveNew might fail to set
a query's hasSubLinks field after inserting a SubLink in it. Although
all current callers make sure that happens anyway, we've had bugs of that
sort before, and it seemed like a good time to install a proper solution.
Back-patch to 8.4. The problem can be demonstrated clear back to 8.0,
but the fix would be too invasive in earlier branches; not to mention
that people may be depending on the subtly-incorrect behavior. The
8.4 series is new enough that fixing this probably won't cause complaints,
but it might in older branches. Also, 8.4 shows the incorrect behavior
in more cases than older branches do, because it is able to flatten
subqueries in more cases.
by unique-ifying the RHS and then inner-joining to some other relation,
that is not grounds for violating the RHS of some other outer join.
Noticed while regression-testing new GEQO code, which will blindly follow
any path that join_is_legal says is legal, and then complain later if that
leads to a dead end.
I'm not certain that this can result in any visible failure in 8.4: the
mistake may always be masked by the fact that subsequent attempts to join
the rest of the RHS of the other join will fail. But I'm not certain it
can't, either, and it's definitely not operating as intended. So back-patch.
The added regression test depends on the new no-failures-allowed logic
that I'm about to commit in GEQO, so no point back-patching that.
that the sanity checking I added to create_mergejoin_plan() in 8.3 was a
few bricks shy of a load: the mergeclauses could reference pathkeys in a
noncanonical order such as x,y,x, not only cases like x,x,y which is all
that the code had allowed for. The odd cases only turn up when using
redundant clauses in an outer join condition, which is why no one had
noticed before.
making pull_up_sublinks() construct a full-blown JoinExpr tree representation
of IN/EXISTS SubLinks that it is able to convert to semi or anti joins.
This makes pull_up_sublinks() a shade more complex, but the gain in semantic
clarity is worth it. I still have more to do in this area to address the
previously-discussed problems, but this commit in itself fixes at least one
bug in HEAD, as shown by added regression test case.
of any lower outer join, even if it also references the non-nullable side and
so could not get pushed below the outer join anyway. We need this in case
the clause is an OR clause: if it doesn't get marked outerjoin_delayed,
create_or_index_quals() could pull an indexable restriction for the nullable
side out of it, leading to wrong results as demonstrated by today's bug
report from toruvinn. (See added regression test case for an example.)
In principle this has been wrong for quite a while. In practice I don't
think any branch before 8.3 can really show the failure, because
create_or_index_quals() will only pull out indexable conditions, and before
8.3 those were always strict. So though we might have improperly generated
null-extended rows in the outer join, they'd get discarded from the result
anyway. The gating factor that makes the failure visible is that 8.3
considers "col IS NULL" to be indexable. Hence I'm not going to risk
back-patching further than 8.3.
of poorer planning in 8.3 than 8.2:
1. After pushing a constant across an outer join --- ie, given
"a LEFT JOIN b ON (a.x = b.y) WHERE a.x = 42", we can deduce that b.y is
sort of equal to 42, in the sense that we needn't fetch any b rows where
it isn't 42 --- loop to see if any additional deductions can be made.
Previous releases did that by recursing, but I had mistakenly thought that
this was no longer necessary given the EquivalenceClass machinery.
2. Allow pushing constants across outer join conditions even if the
condition is outerjoin_delayed due to a lower outer join. This is safe
as long as the condition is strict and we re-test it at the upper join.
3. Keep the outer-join clause even if we successfully push a constant
across it. This is *necessary* in the outerjoin_delayed case, but
even in the simple case, it seems better to do this to ensure that the
join search order heuristics will consider the join as reasonable to
make. Mark such a clause as having selectivity 1.0, though, since it's
not going to eliminate very many rows after application of the constant
condition.
4. Tweak have_relevant_eclass_joinclause to report that two relations
are joinable when they have vars that are equated to the same constant.
We won't actually generate any joinclause from such an EquivalenceClass,
but again it seems that in such a case it's a good idea to consider
the join as worth costing out.
5. Fix a bug in select_mergejoin_clauses that was exposed by these
changes: we have to reject candidate mergejoin clauses if either side was
equated to a constant, because we can't construct a canonical pathkey list
for such a clause. This is an implementation restriction that might be
worth fixing someday, but it doesn't seem critical to get it done for 8.3.
sets for outer joins, in the light of bug #3588 and additional thought and
experimentation. The original methodology was fatally flawed for nests of
more than two outer joins: it got the relationships between adjacent joins
right, but didn't always come to the right conclusions about whether a join
could be interchanged with one two or more levels below it. This was largely
caused by a mistaken idea that we should use the min_lefthand + min_righthand
sets of a sub-join as the minimum left or right input set of an upper join
when we conclude that the sub-join can't commute with the upper one. If
there's a still-lower join that the sub-join *can* commute with, this method
led us to think that that one could commute with the topmost join; which it
can't. Another problem (not directly connected to bug #3588) was that
make_outerjoininfo's processing-order-dependent method for enforcing outer
join identity #3 didn't work right: if we decided that join A could safely
commute with lower join B, we dropped all information about sub-joins under B
that join A could perhaps not safely commute with, because we removed B's
entire min_righthand from A's.
To fix, make an explicit computation of all inner join combinations that occur
below an outer join, and add to that the full syntactic relsets of any lower
outer joins that we determine it can't commute with. This method gives much
more direct enforcement of the outer join rearrangement identities, and it
turns out not to cost a lot of additional bookkeeping.
Thanks to Richard Harris for the bug report and test case.
clauses in which one side or the other references both sides of the join
cannot be removed as redundant, because that expression won't have been
constrained below the join. Per report from Sergey Burladyan.
CVS HEAD does not contain this bug due to EquivalenceClass rewrite, but it
seems wise to include the regression test for it anyway.
in cases where a sub-SELECT inserts a WHERE clause between two outer joins,
that clause may prevent us from re-ordering the two outer joins. The code
was considering only the joins' own ON-conditions in determining reordering
safety, which is not good enough. Add a "delay_upper_joins" flag to
OuterJoinInfo to flag that we have detected such a clause and higher-level
outer joins shouldn't be permitted to commute with this one. (This might
seem overly coarse, but given the current rules for OJ reordering, it's
sufficient AFAICT.)
The failure case is actually pretty narrow: it needs a WHERE clause within
the RHS of a left join that checks the RHS of a lower left join, but is not
strict for that RHS (else we'd have simplified the lower join to a plain
join). Even then no failure will be manifest unless the planner chooses to
rearrange the join order.
Per bug report from Adam Terrey.
considered when it is necessary to do so because of a join-order restriction
(that is, an outer-join or IN-subselect construct). The former coding was a
bit ad-hoc and inconsistent, and it missed some cases, as exposed by Mario
Weilguni's recent bug report. His specific problem was that an IN could be
turned into a "clauseless" join due to constant-propagation removing the IN's
joinclause, and if the IN's subselect involved more than one relation and
there was more than one such IN linking to the same upper relation, then the
only valid join orders involve "bushy" plans but we would fail to consider the
specific paths needed to get there. (See the example case added to the join
regression test.) On examining the code I wonder if there weren't some other
problem cases too; in particular it seems that GEQO was defending against a
different set of corner cases than the main planner was. There was also an
efficiency problem, in that when we did realize we needed a clauseless join
because of an IN, we'd consider clauseless joins against every other relation
whether this was sensible or not. It seems a better design is to use the
outer-join and in-clause lists as a backup heuristic, just as the rule of
joining only where there are joinclauses is a heuristic: we'll join two
relations if they have a usable joinclause *or* this might be necessary to
satisfy an outer-join or IN-clause join order restriction. I refactored the
code to have just one place considering this instead of three, and made sure
that it covered all the cases that any of them had been considering.
Backpatch as far as 8.1 (which has only the IN-clause form of the disease).
By rights 8.0 and 7.4 should have the bug too, but they accidentally fail
to fail, because the joininfo structure used in those releases preserves some
memory of there having once been a joinclause between the inner and outer
sides of an IN, and so it leads the code in the right direction anyway.
I'll be conservative and not touch them.
2005-05-13. When we find that a new inner tuple can't possibly match any
outer tuple (because it contains a NULL), we can't immediately skip the
tuple when we are in NEXTINNER state. Doing so can lead to emitting
multiple copies of the tuple in FillInner mode, because we may rescan the
tuple after returning to a previous marked tuple. Instead, proceed to
NEXTOUTER state the same as we used to do. After we've found that there's
no need to return to the marked position, we can go to SKIPINNER_ADVANCE
state instead of SKIP_TEST when the inner tuple is unmatchable; this
preserves the performance improvement. Per bug report from Bruce.
I also made a couple of cosmetic code rearrangements and added a regression
test for the problem.
not likely ever to be implemented seeing it's been removed from SQL2003.
This allows getting rid of the 'filter' version of yylex() that we had in
parser.c, which should save at least a few microseconds in parsing.
in UPDATE. We also now issue a NOTICE if a query has _any_ implicit
range table entries -- in the past, we would only warn about implicit
RTEs in SELECTs with at least one explicit RTE.
As a result of the warning change, 25 of the regression tests had to
be updated. I also took the opportunity to remove some bogus whitespace
differences between some of the float4 and float8 variants. I believe
I have correctly updated all the platform-specific variants, but let
me know if that's not the case.
Original patch for DELETE ... USING from Euler Taveira de Oliveira,
reworked by Neil Conway.
better make sure the sort order is totally specified; else we get burnt
by platform-specific behavior of qsort() with equal keys. Per buildfarm
results.
In particular, there was a mathematical tie between the two possible
nestloop-with-materialized-inner-scan plans for a join (ie, we computed
the same cost with either input on the inside), resulting in a roundoff
error driven choice, if the relations were both small enough to fit in
sort_mem. Add a small cost factor to ensure we prefer materializing the
smaller input. This changes several regression test plans, but with any
luck we will now have more stability across platforms.
subplan it starts with, as they may be needed at upper join levels.
See comments added to code for the non-obvious reason why. Per bug report
from Robert Creager.
constraints appearing in outer-join qualification clauses are restricted
as to when and where they can be pushed down. Add regression test
to catch future errors in this area.
lists to join RTEs, attach a list of Vars and COALESCE expressions that will
replace the join's alias variables during planning. This simplifies
flatten_join_alias_vars while still making it easy to fix up varno references
when transforming the query tree. Add regression test cases for interactions
of subqueries with outer joins.
now has an RTE of its own, and references to its outputs now are Vars
referencing the JOIN RTE, rather than CASE-expressions. This allows
reverse-listing in ruleutils.c to use the correct alias easily, rather
than painfully reverse-engineering the alias namespace as it used to do.
Also, nested FULL JOINs work correctly, because the result of the inner
joins are simple Vars that the planner can cope with. This fixes a bug
reported a couple times now, notably by Tatsuo on 18-Nov-01. The alias
Vars are expanded into COALESCE expressions where needed at the very end
of planning, rather than during parsing.
Also, beginnings of support for showing plan qualifier expressions in
EXPLAIN. There are probably still cases that need work.
initdb forced due to change of stored-rule representation.
Tom Lane
Bruce Momjian
Peter Eisentraut
Neil Conway
Thomas G. Lockhart