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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2009-10-28 14:55:47 +0000 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2009-10-28 14:55:47 +0000 |
| commit | 46e3a16b050a23b924e5d8a75c8bb7068c26aa96 (patch) | |
| tree | 3832d199195ba326e6a3a1a2f48534dd83a9bddc /src/backend/nodes/outfuncs.c | |
| parent | 44956c52c5fef0b2bb541e959bd65910949eb15f (diff) | |
| download | postgresql-46e3a16b050a23b924e5d8a75c8bb7068c26aa96.tar.gz | |
When FOR UPDATE/SHARE is used with LIMIT, put the LockRows plan node
underneath the Limit node, not atop it. This fixes the old problem that such
a query might unexpectedly return fewer rows than the LIMIT says, due to
LockRows discarding updated rows.
There is a related problem that LockRows might destroy the sort ordering
produced by earlier steps; but fixing that by pushing LockRows below Sort
would create serious performance problems that are unjustified in many
real-world applications, as well as potential deadlock problems from locking
many more rows than expected. Instead, keep the present semantics of applying
FOR UPDATE after ORDER BY within a single query level; but allow the user to
specify the other way by writing FOR UPDATE in a sub-select. To make that
work, track whether FOR UPDATE appeared explicitly in sub-selects or got
pushed down from the parent, and don't flatten a sub-select that contained an
explicit FOR UPDATE.
Diffstat (limited to 'src/backend/nodes/outfuncs.c')
| -rw-r--r-- | src/backend/nodes/outfuncs.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c index ae7a859bd5..7abee7a2d8 100644 --- a/src/backend/nodes/outfuncs.c +++ b/src/backend/nodes/outfuncs.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.370 2009/10/26 02:26:31 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.371 2009/10/28 14:55:38 tgl Exp $ * * NOTES * Every node type that can appear in stored rules' parsetrees *must* @@ -1987,6 +1987,7 @@ _outQuery(StringInfo str, Query *node) WRITE_BOOL_FIELD(hasSubLinks); WRITE_BOOL_FIELD(hasDistinctOn); WRITE_BOOL_FIELD(hasRecursive); + WRITE_BOOL_FIELD(hasForUpdate); WRITE_NODE_FIELD(cteList); WRITE_NODE_FIELD(rtable); WRITE_NODE_FIELD(jointree); @@ -2036,6 +2037,7 @@ _outRowMarkClause(StringInfo str, RowMarkClause *node) WRITE_UINT_FIELD(rti); WRITE_BOOL_FIELD(forUpdate); WRITE_BOOL_FIELD(noWait); + WRITE_BOOL_FIELD(pushedDown); } static void |