Re: slow, long-running 'commit prepared'

On Tue, Nov 25, 2008 at 07:17:20PM -0800, John Smith wrote:
> I have a pg instance with 700GB of data, almost all of which is in one
> table. When I PREPARE and then COMMIT PREPARED a transaction that
> reads & writes to a large fraction of that data (about 10%,
> effectively randomly chosen rows and so every file in the table is
> modified), the COMMIT PREPARED sometimes takes a very long time--2 to
> 5 minutes. Is this expected? Is it possible for the commit to hang
> waiting on some lock for this long? I haven't yet been able to examine
> pg_locks during this 5 minute delay. There is very little
> concurrency--only a couple of open sessions--when the COMMIT PREPARED
> is issued.

You could be I/O bound. Have a look at iostat and sar.

A
--
Andrew Sullivan
ajs(at)crankycanuck(dot)ca