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Avoid unnecessary failure in SELECT concurrent with ALTER NO INHERIT.

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If a query against an inheritance tree runs concurrently with an ALTER
TABLE that's disinheriting one of the tree members, it's possible to get
a "could not find inherited attribute" error because after obtaining lock
on the removed member, make_inh_translation_list sees that its columns
have attinhcount=0 and decides they aren't the columns it's looking for.

An ideal fix, perhaps, would avoid including such a just-removed member
table in the query at all; but there seems no way to accomplish that
without adding expensive catalog rechecks or creating a likelihood of
deadlocks.  Instead, let's just drop the check on attinhcount.  In this
way, a query that's included a just-disinherited child will still
succeed, which is not a completely unreasonable behavior.

This problem has existed for a long time, so back-patch to all supported
branches.  Also add an isolation test verifying related behaviors.

Patch by me; the new isolation test is based on Kyotaro Horiguchi's work.

Discussion: https://postgr.es/m/20170626.174612.23936762.horiguchi.kyotaro@lab.ntt.co.jp
This commit is contained in:
Tom Lane
2018-01-12 15:46:37 -05:00
parent 6520d4a969
commit c2a7044a51
4 changed files with 97 additions and 2 deletions
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4
src/backend/optimizer/prep/prepunion.c
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@@ -1638,7 +1638,7 @@ make_inh_translation_list(Relation oldrelation, Relation newrelation,
*/
if (old_attno < newnatts &&
(att = new_tupdesc->attrs[old_attno]) != NULL &&
!att->attisdropped && att->attinhcount != 0 &&
!att->attisdropped &&
strcmp(attname, NameStr(att->attname)) == 0)
new_attno = old_attno;
else
@@ -1646,7 +1646,7 @@ make_inh_translation_list(Relation oldrelation, Relation newrelation,
for (new_attno = 0; new_attno < newnatts; new_attno++)
{
att = new_tupdesc->attrs[new_attno];
if (!att->attisdropped && att->attinhcount != 0 &&
if (!att->attisdropped &&
strcmp(attname, NameStr(att->attname)) == 0)
break;
}