The previous coding essentially assumed that nodes would be rescanned in
the same order they were initialized in; or at least that the "leader" of
a group of CTEscans would be rescanned before any others were required to
execute. Unfortunately, that isn't even a little bit true. It's possible
to devise queries in which the leader isn't rescanned until other CTEscans
on the same CTE have run to completion, or even in which the leader never
gets a rescan call at all.
The fix makes the leader specially responsible only for initial creation
and final destruction of the tuplestore; rescan resets are now a
symmetrically shared responsibility. This means that we might reset the
tuplestore multiple times when restarting a plan subtree containing
multiple CTEscans; but resetting an already-empty tuplestore is cheap
enough that that doesn't seem like a problem.
Per report from Adam Mackler; the new regression test cases are based on
his example query.
Back-patch to 8.4 where CTE scans were introduced.
Parse analysis neglected to cover the case of a WITH clause attached to an
intermediate-level set operation; it only handled WITH at the top level
or WITH attached to a leaf-level SELECT. Per report from Adam Mackler.
In HEAD, I rearranged the order of SelectStmt's fields to put withClause
with the other fields that can appear on non-leaf SelectStmts. In back
branches, leave it alone to avoid a possible ABI break for third-party
code.
Back-patch to 8.4 where WITH support was added.
setrefs.c failed to do "rtoffset" adjustment of Vars in RETURNING lists,
which meant they were left with the wrong varnos when the RETURNING list
was in a subquery. That was never possible before writable CTEs, of
course, but now it's broken. The executor fails to notice any problem
because ExecEvalVar just references the ecxt_scantuple for any normal
varno; but EXPLAIN breaks when the varno is wrong, as illustrated in a
recent complaint from Bartosz Dmytrak.
Since the eventual rtoffset of the subquery is not known at the time
we are preparing its plan node, the previous scheme of executing
set_returning_clause_references() at that time cannot handle this
adjustment. Fortunately, it turns out that we don't really need to do it
that way, because all the needed information is available during normal
setrefs.c execution; we just have to dig it out of the ModifyTable node.
So, do that, and get rid of the kluge of early setrefs processing of
RETURNING lists. (This is a little bit of a cheat in the case of inherited
UPDATE/DELETE, because we are not passing a "root" struct that corresponds
exactly to what the subplan was built with. But that doesn't matter, and
anyway this is less ugly than early setrefs processing was.)
Back-patch to 9.1, where the problem became possible to hit.
Formerly we passed an empty list to each per-child-table invocation of
grouping_planner, and then merged the results into the global list.
However, that fails if there's a CTE attached to the statement, because
create_ctescan_plan uses the list to find the plan referenced by a CTE
reference; so it was unable to find any CTEs attached to the outer UPDATE
or DELETE. But there's no real reason not to use the same list throughout
the process, and doing so is simpler and faster anyway.
Per report from Josh Berkus of "could not find plan for CTE" failures.
Back-patch to 9.1 where we added support for WITH attached to UPDATE or
DELETE. Add some regression test cases, too.
Since the original implementation of CTEs only allowed them in SELECT
queries, the rule rewriter did not expect to find any CTEs in statements
being rewritten by ON INSERT/UPDATE/DELETE rules. We had dealt with this
to some extent but the code was still several bricks shy of a load, as
illustrated in bug #6051 from Jehan-Guillaume de Rorthais.
In particular, we have to be able to copy CTEs from the original query's
cteList into that of a rule action, in case the rule action references the
CTE (which it pretty much always will). This also implies we were doing
things in the wrong order in RewriteQuery: we have to recursively rewrite
the CTE queries before expanding the main query, so that we have the
rewritten queries available to copy.
There are unpleasant limitations yet to resolve here, but at least we now
throw understandable FEATURE_NOT_SUPPORTED errors for them instead of just
failing with bizarre implementation-dependent errors. In particular, we
can't handle propagating the same CTE into multiple post-rewrite queries
(because then the CTE would be evaluated multiple times), and we can't cope
with conflicts between CTE names in the original query and in the rule
actions.
The originally committed patch for modifying CTEs didn't interact well
with EXPLAIN, as noted by myself, and also had corner-case problems with
triggers, as noted by Dean Rasheed. Those problems show it is really not
practical for ExecutorEnd to call any user-defined code; so split the
cleanup duties out into a new function ExecutorFinish, which must be called
between the last ExecutorRun call and ExecutorEnd. Some Asserts have been
added to these functions to help verify correct usage.
It is no longer necessary for callers of the executor to call
AfterTriggerBeginQuery/AfterTriggerEndQuery for themselves, as this is now
done by ExecutorStart/ExecutorFinish respectively. If you really need to
suppress that and do it for yourself, pass EXEC_FLAG_SKIP_TRIGGERS to
ExecutorStart.
Also, refactor portal commit processing to allow for the possibility that
PortalDrop will invoke user-defined code. I think this is not actually
necessary just yet, since the portal-execution-strategy logic forces any
non-pure-SELECT query to be run to completion before we will consider
committing. But it seems like good future-proofing.
We need ExecutorEnd to run the ModifyTable nodes to completion in
reverse order of initialization, not forward order. Easily done
by constructing the list back-to-front.
This patch implements data-modifying WITH queries according to the
semantics that the updates all happen with the same command counter value,
and in an unspecified order. Therefore one WITH clause can't see the
effects of another, nor can the outer query see the effects other than
through the RETURNING values. And attempts to do conflicting updates will
have unpredictable results. We'll need to document all that.
This commit just fixes the code; documentation updates are waiting on
author.
Marko Tiikkaja and Hitoshi Harada
This is not the hoped-for facility of using INSERT/UPDATE/DELETE inside
a WITH, but rather the other way around. It seems useful in its own
right anyway.
Note: catversion bumped because, although the contents of stored rules
might look compatible, there's actually a subtle semantic change.
A single Query containing a WITH and INSERT...VALUES now represents
writing the WITH before the INSERT, not before the VALUES. While it's
not clear that that matters to anyone, it seems like a good idea to
have it cited in the git history for catversion.h.
Original patch by Marko Tiikkaja, with updating and cleanup by
Hitoshi Harada.
code was already okay with this, but the hack that obtained the output
column types of a recursive union in advance of doing real parse analysis
of the recursive union forgot to handle the case where there was an inner
WITH clause available to the non-recursive term. Best fix seems to be to
refactor so that we don't need the "throwaway" parse analysis step at all.
Instead, teach the transformSetOperationStmt code to set up the CTE's output
column information after it's processed the non-recursive term normally.
Per report from David Fetter.
the "cteParam" as a proxy for the possibility that the underlying CTE plan
depends on outer-level variables or Params, but that doesn't work very well
because it sometimes causes calling subqueries to be treated as SubPlans when
they could be InitPlans. This is inefficient and also causes the outright
failure exhibited in bug #4902. Instead, leave the cteParam out of it and
copy the underlying CTE plan's extParams directly. Per bug #4902 from
Marko Tiikkaja.
TupleTableSlots. We have functions for retrieving a minimal tuple from a slot
after storing a regular tuple in it, or vice versa; but these were implemented
by converting the internal storage from one format to the other. The problem
with that is it invalidates any pass-by-reference Datums that were already
fetched from the slot, since they'll be pointing into the just-freed version
of the tuple. The known problem cases involve fetching both a whole-row
variable and a pass-by-reference value from a slot that is fed from a
tuplestore or tuplesort object. The added regression tests illustrate some
simple cases, but there may be other failure scenarios traceable to the same
bug. Note that the added tests probably only fail on unpatched code if it's
built with --enable-cassert; otherwise the bug leads to fetching from freed
memory, which will not have been overwritten without additional conditions.
Fix by allowing a slot to contain both formats simultaneously; which turns out
not to complicate the logic much at all, if anything it seems less contorted
than before.
Back-patch to 8.2, where minimal tuples were introduced.
depth-first search order. Upon close reading of SQL:2008, it seems that the
spec's SEARCH DEPTH FIRST and SEARCH BREADTH FIRST options do not actually
guarantee any particular result order: what they do is provide a constructed
column that the user can then sort on in the outer query. So this is actually
just as much functionality ...
pseudo-type record[] to represent arrays of possibly-anonymous composite
types. Since composite datums carry their own type identification, no
extra knowledge is needed at the array level.
The main reason for doing this right now is that it is necessary to support
the general case of detection of cycles in recursive queries: if you need to
compare more than one column to detect a cycle, you need to compare a ROW()
to an array built from ROW()s, at least if you want to do it as the spec
suggests. Add some documentation and regression tests concerning the cycle
detection issue.
RecursiveUnion to which it refers. It turns out that we can just postpone the
relevant initialization steps until the first exec call for the node, by which
time the ancestor node must surely be initialized. Per report from Greg Stark.
implementation uses an in-memory hash table, so it will poop out for very
large recursive results ... but the performance characteristics of a
sort-based implementation would be pretty unpleasant too.
recursive CTE that we're still in progress of analyzing. Add a similar guard
to the similar code in expandRecordVariable(), and tweak regression tests to
cover this case. Per report from Dickson S. Guedes.
There are some unimplemented aspects: recursive queries must use UNION ALL
(should allow UNION too), and we don't have SEARCH or CYCLE clauses.
These might or might not get done for 8.4, but even without them it's a
pretty useful feature.
There are also a couple of small loose ends and definitional quibbles,
which I'll send a memo about to pgsql-hackers shortly. But let's land
the patch now so we can get on with other development.
Yoshiyuki Asaba, with lots of help from Tatsuo Ishii and Tom Lane
Tom Lane