Ned Wolpert <ned(dot)wolpert(at)imemories(dot)com> writes:
> Event: Running 9.1.6 with hot-standby, archiving 4 months of wal files,
> and even a nightly pg_dump all. 50G database. Trying to update or delete a
> row in a small (21 row, but heavily used table) would lock up completely.
> Never finish. Removed all clients, restarted the db instance, no joy. Check
> pg_stat_activity, and nothing that wasn't idle.... run the delete, locked
> up.
I'm betting one of those prepared transactions had updated or deleted
this row, and thus held a row lock on it. (Come to think of it, a
SELECT FOR UPDATE/SHARE might have been enough.) Did you try committing
or rolling back those xacts?
regards, tom lane