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Fix possible "tuple concurrently updated" error in ALTER TABLE.

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When adding an inheritance parent to a table, an AccessShareLock on the
parent isn't strong enough to prevent trouble, so take
ShareUpdateExclusiveLock instead.  Since this is a behavior change,
albeit a fairly unobtrusive one, and since we have only one report
from the field, no back-patch.

Report by Jon Nelson, analysis by Alvaro Herrera, fix by me.
This commit is contained in:
Robert Haas 2011-03-18 22:09:57 -04:00
parent 727589995a
commit fbcf4b92aa
1 changed files with 11 additions and 4 deletions
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15
src/backend/commands/tablecmds.c
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@ -1345,7 +1345,14 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
AttrNumber *newattno;
AttrNumber parent_attno;
relation = heap_openrv(parent, AccessShareLock);
/*
* A self-exclusive lock is needed here. If two backends attempt to
* add children to the same parent simultaneously, and that parent has
* no pre-existing children, then both will attempt to update the
* parent's relhassubclass field, leading to a "tuple concurrently
* updated" error.
*/
relation = heap_openrv(parent, ShareUpdateExclusiveLock);
if (relation->rd_rel->relkind != RELKIND_RELATION)
ereport(ERROR,
@ -7942,10 +7949,10 @@ ATExecAddInherit(Relation child_rel, RangeVar *parent, LOCKMODE lockmode)
List *children;
/*
* AccessShareLock on the parent is what's obtained during normal CREATE
* TABLE ... INHERITS ..., so should be enough here.
* A self-exclusive lock is needed here. See the similar case in
* MergeAttributes() for a full explanation.
*/
parent_rel = heap_openrv(parent, AccessShareLock);
parent_rel = heap_openrv(parent, ShareUpdateExclusiveLock);
/*
* Must be owner of both parent and child -- child was checked by