diff options
| -rw-r--r-- | src/backend/optimizer/plan/setrefs.c | 24 |
1 files changed, 20 insertions, 4 deletions
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c index e44ae971b4b..a7b11b7f03a 100644 --- a/src/backend/optimizer/plan/setrefs.c +++ b/src/backend/optimizer/plan/setrefs.c @@ -1512,8 +1512,16 @@ set_append_references(PlannerInfo *root, lfirst(l) = set_plan_refs(root, (Plan *) lfirst(l), rtoffset); } - /* Now, if there's just one, forget the Append and return that child */ - if (list_length(aplan->appendplans) == 1) + /* + * See if it's safe to get rid of the Append entirely. For this to be + * safe, there must be only one child plan and that child plan's parallel + * awareness must match that of the Append's. The reason for the latter + * is that the if the Append is parallel aware and the child is not then + * the calling plan may execute the non-parallel aware child multiple + * times. + */ + if (list_length(aplan->appendplans) == 1 && + ((Plan *) linitial(aplan->appendplans))->parallel_aware == aplan->plan.parallel_aware) return clean_up_removed_plan_level((Plan *) aplan, (Plan *) linitial(aplan->appendplans)); @@ -1576,8 +1584,16 @@ set_mergeappend_references(PlannerInfo *root, lfirst(l) = set_plan_refs(root, (Plan *) lfirst(l), rtoffset); } - /* Now, if there's just one, forget the MergeAppend and return that child */ - if (list_length(mplan->mergeplans) == 1) + /* + * See if it's safe to get rid of the MergeAppend entirely. For this to + * be safe, there must be only one child plan and that child plan's + * parallel awareness must match that of the MergeAppend's. The reason + * for the latter is that the if the MergeAppend is parallel aware and the + * child is not then the calling plan may execute the non-parallel aware + * child multiple times. + */ + if (list_length(mplan->mergeplans) == 1 && + ((Plan *) linitial(mplan->mergeplans))->parallel_aware == mplan->plan.parallel_aware) return clean_up_removed_plan_level((Plan *) mplan, (Plan *) linitial(mplan->mergeplans)); |