Re: Strange deadlock error last night

"Scott Whitney" <swhitney(at)journyx(dot)com> writes:
> Last night, I got this:

> Jan 13 03:31:28 db01 postgres[23537]: [140-2] DETAIL: Process 23537 waits
> for AccessShareLock on relation 1260 of database 0; blocked by process
> 22228.
> Jan 13 03:31:28 db01 postgres[23537]: [140-3] Process 22228 waits for
> AccessShareLock on relation 1262 of database 0; blocked by process 6816.
> Jan 13 03:31:28 db01 postgres[23537]: [140-4] Process 6816 waits for
> AccessShareLock on relation 1260 of database 0; blocked by process 14624.
> Jan 13 03:31:28 db01 postgres[23537]: [140-5] Process 14624 waits for
> AccessExclusiveLock on relation 1260 of database 0; blocked by process
> 23537.
> Jan 13 03:31:28 db01 postgres[14624]: [243-1] ERROR: deadlock detected

Well, the problem is evidently that guy trying to get exclusive lock on
relation 1260, which is pg_authid (a quick way to check that is "select
1260::regclass"). (Note: the "database 0" just means it's a system catalog
that's shared across all databases.) pg_authid is touched often enough
that trying to ex-lock it in an active database is just asking for
trouble.

Is it possible that that process was trying to run VACUUM FULL or
REINDEX on pg_authid? I can't think of any other likely-sounding
explanation for something trying to take an exclusive lock on that
catalog. The best solution would be "don't do that" ...

> It ended up locking up about 250 customer databases until I restarted the
> postmaster. This is version 8.1.4. Upgrading right now (even to a minor rev)
> is not really an option.

Not related to the immediate problem, but: you really need to schedule
5 minutes' downtime so you can update to 8.1.latest. Reasons can be
found here:
http://www.postgresql.org/docs/8.1/static/release.html

regards, tom lane