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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/copyfuncs.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/copyfuncs.c')
| -rw-r--r-- | src/backend/nodes/copyfuncs.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c index deee9994170..a9efce40532 100644 --- a/src/backend/nodes/copyfuncs.c +++ b/src/backend/nodes/copyfuncs.c @@ -15,7 +15,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.449 2009/10/26 02:26:31 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.450 2009/10/28 14:55:38 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -1859,6 +1859,7 @@ _copyRowMarkClause(RowMarkClause *from) COPY_SCALAR_FIELD(rti); COPY_SCALAR_FIELD(forUpdate); COPY_SCALAR_FIELD(noWait); + COPY_SCALAR_FIELD(pushedDown); return newnode; } @@ -2223,6 +2224,7 @@ _copyQuery(Query *from) COPY_SCALAR_FIELD(hasSubLinks); COPY_SCALAR_FIELD(hasDistinctOn); COPY_SCALAR_FIELD(hasRecursive); + COPY_SCALAR_FIELD(hasForUpdate); COPY_NODE_FIELD(cteList); COPY_NODE_FIELD(rtable); COPY_NODE_FIELD(jointree); |