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Re: PostgreSQL 8.4 performance tuning questions

From: Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>
To: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Matthew Wakeling <matthew(at)flymine(dot)org>, pgsql-performance(at)postgresql(dot)org
Subject: Re: PostgreSQL 8.4 performance tuning questions
Date: 2009-07-30 18:24:25
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Kevin Grittner wrote:
> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote: 
>> "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
>>> Since the dump to custom format ran longer than the full pg_dump
>>> piped directly to psql would have taken, the overall time to use
>>> this technique is clearly longer for our databases on our hardware.
>> Hmmm ... AFAIR there isn't a good reason for dump to custom format
>> to take longer than plain text dump, except for applying
>> compression.  Maybe -Z0 would be worth testing?  Or is the problem
>> that you have to write the data to a disk file rather than just
>> piping it?
> I did some checking with the DBA who normally copies these around for
> development and test environments.  He confirmed that when the source
> and target are on the same machine, a pg_dump piped to psql takes
> about two hours.  If he pipes across the network, it runs more like
> three hours.
> My pg_dump to custom format ran for six hours.  The single-transaction
> restore from that dump file took two hours, with both on the same
> machine.  I can confirm with benchmarks, but this guy generally knows
> what he's talking about (and we do create a lot of development and
> test databases this way).
> Either the compression is tripling the dump time, or there is
> something inefficient about how pg_dump writes to the disk.

seems about right - compression in pg_dump -Fc is a serious bottleneck 
and unless can significantly speed it up or make it use of multiple 
cores (either for the dump itself - which would be awsome - or for the 
compression) I would recommend to not use it at all.


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