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Fix matching of boolean index columns to sort ordering.

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Normally, if we have a WHERE clause like "indexcol = constant",
the planner will figure out that that index column can be ignored
when determining whether the index has a desired sort ordering.
But this failed to work for boolean index columns, because a
condition like "boolcol = true" is canonicalized to just "boolcol"
which does not give rise to an EquivalenceClass.  Add a check to
allow the same type of deduction to be made in this case too.

Per a complaint from Dima Pavlov.  Arguably this is a bug, but given the
limited impact and the small number of complaints so far, I won't risk
destabilizing plans in stable branches by back-patching.

Patch by me, reviewed by Michael Paquier

Discussion: https://postgr.es/m/1788.1481605684@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2017-01-15 14:09:35 -05:00
parent 83f2061dd0
commit 0777f7a2e8
5 changed files with 129 additions and 11 deletions
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35
src/backend/optimizer/path/pathkeys.c
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@@ -480,17 +480,30 @@ build_index_pathkeys(PlannerInfo *root,
index->rel->relids,
false);
/*
* If the sort key isn't already present in any EquivalenceClass, then
* it's not an interesting sort order for this query. So we can stop
* now --- lower-order sort keys aren't useful either.
*/
if (!cpathkey)
break;
/* Add to list unless redundant */
if (!pathkey_is_redundant(cpathkey, retval))
retval = lappend(retval, cpathkey);
if (cpathkey)
{
/*
* We found the sort key in an EquivalenceClass, so it's relevant
* for this query. Add it to list, unless it's redundant.
*/
if (!pathkey_is_redundant(cpathkey, retval))
retval = lappend(retval, cpathkey);
}
else
{
/*
* Boolean index keys might be redundant even if they do not
* appear in an EquivalenceClass, because of our special treatment
* of boolean equality conditions --- see the comment for
* indexcol_is_bool_constant_for_query(). If that applies, we can
* continue to examine lower-order index columns. Otherwise, the
* sort key is not an interesting sort order for this query, so we
* should stop considering index columns; any lower-order sort
* keys won't be useful either.
*/
if (!indexcol_is_bool_constant_for_query(index, i))
break;
}
i++;
}