mirror of
https://github.com/postgres/postgres.git
synced 2025-07-08 11:42:09 +03:00
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.
This commit is contained in:
@ -8,7 +8,7 @@
|
||||
*
|
||||
*
|
||||
* IDENTIFICATION
|
||||
* $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.260 2009/10/26 02:26:33 tgl Exp $
|
||||
* $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.261 2009/10/28 14:55:38 tgl Exp $
|
||||
*
|
||||
*-------------------------------------------------------------------------
|
||||
*/
|
||||
@ -1638,19 +1638,7 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
|
||||
}
|
||||
|
||||
/*
|
||||
* If there is a LIMIT/OFFSET clause, add the LIMIT node.
|
||||
*/
|
||||
if (parse->limitCount || parse->limitOffset)
|
||||
{
|
||||
result_plan = (Plan *) make_limit(result_plan,
|
||||
parse->limitOffset,
|
||||
parse->limitCount,
|
||||
offset_est,
|
||||
count_est);
|
||||
}
|
||||
|
||||
/*
|
||||
* Finally, if there is a FOR UPDATE/SHARE clause, add the LockRows node.
|
||||
* If there is a FOR UPDATE/SHARE clause, add the LockRows node.
|
||||
* (Note: we intentionally test parse->rowMarks not root->rowMarks here.
|
||||
* If there are only non-locking rowmarks, they should be handled by
|
||||
* the ModifyTable node instead.)
|
||||
@ -1660,6 +1648,23 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
|
||||
result_plan = (Plan *) make_lockrows(result_plan,
|
||||
root->rowMarks,
|
||||
SS_assign_special_param(root));
|
||||
/*
|
||||
* The result can no longer be assumed sorted, since locking might
|
||||
* cause the sort key columns to be replaced with new values.
|
||||
*/
|
||||
current_pathkeys = NIL;
|
||||
}
|
||||
|
||||
/*
|
||||
* Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node.
|
||||
*/
|
||||
if (parse->limitCount || parse->limitOffset)
|
||||
{
|
||||
result_plan = (Plan *) make_limit(result_plan,
|
||||
parse->limitOffset,
|
||||
parse->limitCount,
|
||||
offset_est,
|
||||
count_est);
|
||||
}
|
||||
|
||||
/* Compute result-relations list if needed */
|
||||
@ -1795,20 +1800,33 @@ preprocess_rowmarks(PlannerInfo *root)
|
||||
|
||||
/*
|
||||
* Convert RowMarkClauses to PlanRowMark representation.
|
||||
*
|
||||
* Note: currently, it is syntactically impossible to have FOR UPDATE
|
||||
* applied to an update/delete target rel. If that ever becomes
|
||||
* possible, we should drop the target from the PlanRowMark list.
|
||||
*/
|
||||
prowmarks = NIL;
|
||||
foreach(l, parse->rowMarks)
|
||||
{
|
||||
RowMarkClause *rc = (RowMarkClause *) lfirst(l);
|
||||
PlanRowMark *newrc = makeNode(PlanRowMark);
|
||||
RangeTblEntry *rte = rt_fetch(rc->rti, parse->rtable);
|
||||
PlanRowMark *newrc;
|
||||
|
||||
/*
|
||||
* Currently, it is syntactically impossible to have FOR UPDATE
|
||||
* applied to an update/delete target rel. If that ever becomes
|
||||
* possible, we should drop the target from the PlanRowMark list.
|
||||
*/
|
||||
Assert(rc->rti != parse->resultRelation);
|
||||
|
||||
/*
|
||||
* Ignore RowMarkClauses for subqueries; they aren't real tables
|
||||
* and can't support true locking. Subqueries that got flattened
|
||||
* into the main query should be ignored completely. Any that didn't
|
||||
* will get ROW_MARK_COPY items in the next loop.
|
||||
*/
|
||||
if (rte->rtekind != RTE_RELATION)
|
||||
continue;
|
||||
|
||||
rels = bms_del_member(rels, rc->rti);
|
||||
|
||||
newrc = makeNode(PlanRowMark);
|
||||
newrc->rti = newrc->prti = rc->rti;
|
||||
if (rc->forUpdate)
|
||||
newrc->markType = ROW_MARK_EXCLUSIVE;
|
||||
@ -1838,7 +1856,6 @@ preprocess_rowmarks(PlannerInfo *root)
|
||||
continue;
|
||||
|
||||
newrc = makeNode(PlanRowMark);
|
||||
|
||||
newrc->rti = newrc->prti = i;
|
||||
/* real tables support REFERENCE, anything else needs COPY */
|
||||
if (rte->rtekind == RTE_RELATION)
|
||||
|
Reference in New Issue
Block a user