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Fix EquivalenceClass processing for nested append relations.

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The original coding of EquivalenceClasses didn't foresee that appendrel
child relations might themselves be appendrels; but this is possible for
example when a UNION ALL subquery scans a table with inheritance children.
The oversight led to failure to optimize ordering-related issues very well
for the grandchild tables.  After some false starts involving explicitly
flattening the appendrel representation, we found that this could be fixed
easily by removing a few implicit assumptions about appendrel parent rels
not being children themselves.

Kyotaro Horiguchi and Tom Lane, reviewed by Noah Misch
This commit is contained in:
Tom Lane
2014-03-28 11:50:01 -04:00
parent b777be0d48
commit a87c729153
5 changed files with 101 additions and 9 deletions
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20
src/backend/optimizer/path/allpaths.c
View File

@ -1021,10 +1021,15 @@ get_cheapest_parameterized_child_path(PlannerInfo *root, RelOptInfo *rel,
* accumulate_append_subpath
* Add a subpath to the list being built for an Append or MergeAppend
*
* It's possible that the child is itself an Append path, in which case
* we can "cut out the middleman" and just add its child paths to our
* own list. (We don't try to do this earlier because we need to
* apply both levels of transformation to the quals.)
* It's possible that the child is itself an Append or MergeAppend path, in
* which case we can "cut out the middleman" and just add its child paths to
* our own list. (We don't try to do this earlier because we need to apply
* both levels of transformation to the quals.)
*
* Note that if we omit a child MergeAppend in this way, we are effectively
* omitting a sort step, which seems fine: if the parent is to be an Append,
* its result would be unsorted anyway, while if the parent is to be a
* MergeAppend, there's no point in a separate sort on a child.
*/
static List *
accumulate_append_subpath(List *subpaths, Path *path)
@ -1036,6 +1041,13 @@ accumulate_append_subpath(List *subpaths, Path *path)
/* list_copy is important here to avoid sharing list substructure */
return list_concat(subpaths, list_copy(apath->subpaths));
}
else if (IsA(path, MergeAppendPath))
{
MergeAppendPath *mpath = (MergeAppendPath *) path;
/* list_copy is important here to avoid sharing list substructure */
return list_concat(subpaths, list_copy(mpath->subpaths));
}
else
return lappend(subpaths, path);
}

12
src/backend/optimizer/path/equivclass.c
View File

@ -1937,16 +1937,20 @@ add_child_rel_equivalences(PlannerInfo *root,
if (cur_ec->ec_has_volatile)
continue;
/* No point in searching if parent rel not mentioned in eclass */
if (!bms_is_subset(parent_rel->relids, cur_ec->ec_relids))
/*
* No point in searching if parent rel not mentioned in eclass; but
* we can't tell that for sure if parent rel is itself a child.
*/
if (parent_rel->reloptkind == RELOPT_BASEREL &&
!bms_is_subset(parent_rel->relids, cur_ec->ec_relids))
continue;
foreach(lc2, cur_ec->ec_members)
{
EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
if (cur_em->em_is_const || cur_em->em_is_child)
continue; /* ignore consts and children here */
if (cur_em->em_is_const)
continue; /* ignore consts here */
/* Does it reference parent_rel? */
if (bms_overlap(cur_em->em_relids, parent_rel->relids))