mirrors/postgres
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Allow RTE_SUBQUERY rels to be considered parallel-safe.

Browse Source 
There isn't really any reason not to; the original comments here were
partly confused about subplans versus subquery-in-FROM, and partly
dependent on restrictions that no longer apply now that subqueries return
Paths not Plans.  Depending on what's inside the subquery, it might fail
to produce any parallel_safe Paths, but that's fine.

Tom Lane and Robert Haas
This commit is contained in:
Tom Lane 2016-07-03 18:24:49 -04:00
parent 4ea9948e58
commit 110a6dbdeb
1 changed files with 12 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
src/backend/optimizer/path/allpaths.c
View File

@ -575,15 +575,19 @@ set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel,
case RTE_SUBQUERY: case RTE_SUBQUERY:
/* /*
* Subplans currently aren't passed to workers. Even if they * There's no intrinsic problem with scanning a subquery-in-FROM
* were, the subplan might be using parallelism internally, and we * (as distinct from a SubPlan or InitPlan) in a parallel worker.
* can't support nested Gather nodes at present. Finally, we * If the subquery doesn't happen to have any parallel-safe paths,
* don't have a good way of knowing whether the subplan involves * then flagging it as consider_parallel won't change anything,
* any parallel-restricted operations. It would be nice to relax * but that's true for plain tables, too. We must set
* this restriction some day, but it's going to take a fair amount * consider_parallel based on the rel's own quals and targetlist,
* of work. * so that if a subquery path is parallel-safe but the quals and
* projection we're sticking onto it are not, we correctly mark
* 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.)
*/ */
return; break;
case RTE_JOIN: case RTE_JOIN:
/* Shouldn't happen; we're only considering baserels here. */ /* Shouldn't happen; we're only considering baserels here. */