Re: Problem with ALTER TABLE - occasional "tuple concurrently updated"

On Thu, Nov 18, 2010 at 10:28 AM, Jon Nelson <jnelson+pgsql@jamponi.net> wr=
ote:
> On Wed, Nov 17, 2010 at 8:57 PM, Robert Haas <robertmhaas@gmail.com> wrot=
e:
>> On Tue, Nov 16, 2010 at 10:48 AM, Jon Nelson <jnelson+pgsql@jamponi.net>=
 wrote:
>>> I have a process which runs in parallel creating tables which, as the
>>> /final/ step in the import, gets SQL much like the following applied:
>>>
>>> ALTER TABLE foo INHERIT bar;
>>>
>>> Periodically, I get this error: =A0tuple concurrently updated
>>
>> The ALTER TABLE generates that error? =A0Is it running concurrently with
>> any other DML? =A0What version of PostgreSQL is this?
>
> Yes, sometimes yes, and 8.4.5.

Any chance you can isolate a reproducible test case?  Maybe a series
of steps to be run in two psql sessions?  Or any idea what DDL might
be running against the parent at the same time?

In the current master branch, it appears that "ALTER TABLE c INHERIT
p" takes a ShareUpdateExclusiveLock on the child, which seems
sufficient, and an AccessShareLock on the parent, which seems like it
might not be; though I'm having a hard time figuring out exactly when
it wouldn't be, especially since in 8.4 I'm fairly sure any ALTER
TABLE command takes an AccessExclusiveLock.

--=20
Robert Haas
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