database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-03 20:02:46 +03:00
Code Activity

Don't allow LIMIT/OFFSET clause within sub-selects to be pushed to workers.

Browse Source 
Allowing sub-select containing LIMIT/OFFSET in workers can lead to
inconsistent results at the top-level as there is no guarantee that the
row order will be fully deterministic.  The fix is to prohibit pushing
LIMIT/OFFSET within sub-selects to workers.

Reported-by: Andrew Fletcher
Bug: 15324
Author: Amit Kapila
Reviewed-by: Dilip Kumar
Backpatch-through: 9.6
Discussion: https://postgr.es/m/153417684333.10284.11356259990921828616@wrigleys.postgresql.org
This commit is contained in:
Amit Kapila
2018-09-14 09:51:47 +05:30
parent a2afcdab8a
commit 830d756590
5 changed files with 40 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
src/backend/optimizer/path/allpaths.c
View File

@ -620,7 +620,20 @@ set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel,
* the SubqueryScanPath as not parallel-safe. (Note that
* set_subquery_pathlist() might push some of these quals down
* into the subquery itself, but that doesn't change anything.)
*
* We can't push sub-select containing LIMIT/OFFSET to workers as
* there is no guarantee that the row order will be fully
* deterministic, and applying LIMIT/OFFSET will lead to
* inconsistent results at the top-level. (In some cases, where
* the result is ordered, we could relax this restriction. But it
* doesn't currently seem worth expending extra effort to do so.)
*/
{
Query *subquery = castNode(Query, rte->subquery);
if (limit_needed(subquery))
return;
}
break;
case RTE_JOIN: