Re: postmaster 8.2 eternally hangs in sempaphore lock acquiring

Heikki Linnakangas <heikki@enterprisedb.com> writes:
> Tom Lane wrote:
>> This is definitely a bug (I unfortunately didn't see your message until
>> after I'd replicated your reasoning...) but the word from Shuttleworth
>> is that he doesn't see either of those messages in his postmaster log.
>> So it seems we need another theory.  I haven't a clue at the moment though.

> The error message never makes it to the log. The deadlock occurs in the
> PG_CATCH-block, before rethrowing and printing the error.

Oh, of course, I was thinking of the old behavior (still used for fatal
errors), but you're quite right.

> The unsafe elog while holding a lwlock pattern in _bt_vacuum_start needs
> to be fixed, patch attached. We still need to figure out what's causing
> the error in the first place. With the patch, we should at least get a
> proper error message and not hang when the error occurs.

Agreed, that is the next step to take.  I spent quite some time last
night trying to reproduce the failure with no luck (I was using one
process doing create/drop database, one transiently attaching to the
template database, and one doing vacuums).  So I suspect there is an
additional contributing factor in Mark's test case that we haven't
identified yet.

            regards, tom lane