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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/readfuncs.c | |
| parent | 44956c52c5fef0b2bb541e959bd65910949eb15f (diff) | |
| download | postgresql-46e3a16b050a23b924e5d8a75c8bb7068c26aa96.tar.gz postgresql-46e3a16b050a23b924e5d8a75c8bb7068c26aa96.zip | |
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/readfuncs.c')
| -rw-r--r-- | src/backend/nodes/readfuncs.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c index a1520276e22..4192ca7e330 100644 --- a/src/backend/nodes/readfuncs.c +++ b/src/backend/nodes/readfuncs.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/nodes/readfuncs.c,v 1.226 2009/10/26 02:26:32 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/nodes/readfuncs.c,v 1.227 2009/10/28 14:55:38 tgl Exp $ * * NOTES * Path and Plan nodes do not have any readfuncs support, because we @@ -203,6 +203,7 @@ _readQuery(void) READ_BOOL_FIELD(hasSubLinks); READ_BOOL_FIELD(hasDistinctOn); READ_BOOL_FIELD(hasRecursive); + READ_BOOL_FIELD(hasForUpdate); READ_NODE_FIELD(cteList); READ_NODE_FIELD(rtable); READ_NODE_FIELD(jointree); @@ -295,6 +296,7 @@ _readRowMarkClause(void) READ_UINT_FIELD(rti); READ_BOOL_FIELD(forUpdate); READ_BOOL_FIELD(noWait); + READ_BOOL_FIELD(pushedDown); READ_DONE(); } |