Re: [HACKERS] Deadlock with pg_dump? - Mailing list pgsql-patches

I will rework this before application to use LOG level.

Your patch has been added to the PostgreSQL unapplied patches list at:

    http://momjian.postgresql.org/cgi-bin/pgpatches

It will be applied as soon as one of the PostgreSQL committers reviews
and approves it.

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Simon Riggs wrote:
> On Mon, 2007-02-19 at 19:38 +0000, Simon Riggs wrote:
> > On Tue, 2007-02-13 at 22:19 -0500, Bruce Momjian wrote:
> > > Simon Riggs wrote:
> > > > On Thu, 2006-10-26 at 18:45 -0400, Tom Lane wrote:
> > > > > Chris Campbell <chris@bignerdranch.com> writes:
> > > > > > Is there additional logging information I can turn on to get more
> > > > > > details? I guess I need to see exactly what locks both processes
> > > > > > hold, and what queries they were running when the deadlock occurred?
> > > > > > Is that easily done, without turning on logging for *all* statements?
> > > > >
> > > > > log_min_error_statement = error would at least get you the statements
> > > > > reporting the deadlocks, though not what they're conflicting against.
> > > >
> > > > Yeh, we need a much better locking logger for performance analysis.
> > > >
> > > > We really need to dump the whole wait-for graph for deadlocks, since
> > > > this might be more complex than just two statements involved. Deadlocks
> > > > ought to be so infrequent that we can afford the log space to do this -
> > > > plus if we did this it would likely lead to fewer deadlocks.
> > > >
> > > > For 8.3 I'd like to have a log_min_duration_lockwait (secs) parameter
> > > > that would allow you to dump the wait-for graph for any data-level locks
> > > > that wait too long, rather than just those that deadlock. Many
> > > > applications experience heavy locking because of lack of holistic
> > > > design. That will also show up the need for other utilities to act
> > > > CONCURRENTLY, if possible.
> > >
> > > Old email, but I don't see how our current output is not good enough?
> > >
> > >     test=> lock a;
> > >     ERROR:  deadlock detected
> > >     DETAIL:  Process 6855 waits for AccessExclusiveLock on relation 16394 of
> > >     database 16384; blocked by process 6795.
> > >     Process 6795 waits for AccessExclusiveLock on relation 16396 of database
> > >     16384; blocked by process 6855.
> >
> > This detects deadlocks, but it doesn't detect lock waits.
> >
> > When I wrote that it was previous experience driving me. Recent client
> > experience has highlighted the clear need for this. We had a lock wait
> > of 50 hours because of an RI check; thats the kind of thing I'd like to
> > show up in the logs somewhere.
> >
> > Lock wait detection can be used to show up synchronisation points that
> > have been inadvertently designed into an application, so its a useful
> > tool in investigating performance issues.
> >
> > I have a patch implementing the logging as agreed with Tom, will post to
> > patches later tonight.
>
> Patch for discussion, includes doc entries at top of patch, so its
> fairly clear how it works.
>
> Output is an INFO message, to allow this to trigger
> log_min_error_statement when it generates a message, to allow us to see
> the SQL statement that is waiting. This allows it to generate a message
> prior to the statement completing, which is important because it may not
> ever complete, in some cases, so simply logging a list of pids won't
> always tell you what the SQL was that was waiting.
>
> Other approaches are possible...
>
> Comments?
>
> --
>   Simon Riggs
>   EnterpriseDB   http://www.enterprisedb.com
>

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  Bruce Momjian  <bruce@momjian.us>          http://momjian.us
  EnterpriseDB                               http://www.enterprisedb.com

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