database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-02 09:02:37 +03:00
Code Activity

When FOR UPDATE/SHARE is used with LIMIT, put the LockRows plan node

Browse Source 
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.
This commit is contained in:
Tom Lane
2009-10-28 14:55:47 +00:00
parent 44956c52c5
commit 46e3a16b05
13 changed files with 225 additions and 126 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
src/backend/nodes/copyfuncs.c
View File

@ -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);