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Rename find_em_expr_usable_for_sorting_rel.

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I didn't particularly like this function name, as it fails to
express what's going on.  Also, returning the sort expression
alone isn't too helpful --- typically, a caller would also
need some other fields of the EquivalenceMember.  But the
sole caller really only needs a bool result, so let's make
it "bool relation_can_be_sorted_early()".

Discussion: https://postgr.es/m/91f3ec99-85a4-fa55-ea74-33f85a5c651f@swarm64.com
This commit is contained in:
Tom Lane
2021-04-20 11:37:36 -04:00
parent 3753982441
commit 7645376774
3 changed files with 28 additions and 27 deletions
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27
src/backend/optimizer/path/equivclass.c
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@@ -961,18 +961,21 @@ find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel)
}
/*
* Find an equivalence class member expression that can be used to build
* a sort node using the provided relation; return NULL if no candidate.
* relation_can_be_sorted_early
* Can this relation be sorted on this EC before the final output step?
*
* To succeed, we must find an EC member that prepare_sort_from_pathkeys knows
* how to sort on, given the rel's reltarget as input. There are also a few
* additional constraints based on the fact that the desired sort will be done
* within the scan/join part of the plan. Also, non-parallel-safe expressions
* are ignored if 'require_parallel_safe'.
* "early", within the scan/join part of the plan. Also, non-parallel-safe
* expressions are ignored if 'require_parallel_safe'.
*
* At some point we might want to return the identified EquivalenceMember,
* but for now, callers only want to know if there is one.
*/
Expr *
find_em_expr_usable_for_sorting_rel(PlannerInfo *root, EquivalenceClass *ec,
RelOptInfo *rel, bool require_parallel_safe)
bool
relation_can_be_sorted_early(PlannerInfo *root, RelOptInfo *rel,
EquivalenceClass *ec, bool require_parallel_safe)
{
PathTarget *target = rel->reltarget;
EquivalenceMember *em;
@@ -982,7 +985,7 @@ find_em_expr_usable_for_sorting_rel(PlannerInfo *root, EquivalenceClass *ec,
* Reject volatile ECs immediately; such sorts must always be postponed.
*/
if (ec->ec_has_volatile)
return NULL;
return false;
/*
* Try to find an EM directly matching some reltarget member.
@@ -1012,7 +1015,7 @@ find_em_expr_usable_for_sorting_rel(PlannerInfo *root, EquivalenceClass *ec,
!is_parallel_safe(root, (Node *) em->em_expr))
continue;
return em->em_expr;
return true;
}
/*
@@ -1021,7 +1024,7 @@ find_em_expr_usable_for_sorting_rel(PlannerInfo *root, EquivalenceClass *ec,
em = find_computable_ec_member(root, ec, target->exprs, rel->relids,
require_parallel_safe);
if (!em)
return NULL;
return false;
/*
* Reject expressions involving set-returning functions, as those can't be
@@ -1030,9 +1033,9 @@ find_em_expr_usable_for_sorting_rel(PlannerInfo *root, EquivalenceClass *ec,
* belong to multi-member ECs.)
*/
if (IS_SRF_CALL((Node *) em->em_expr))
return NULL;
return false;
return em->em_expr;
return true;
}
/*