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Re: PostgreSQL 8.4 performance tuning questions

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "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 18:14:30
Message-ID: 4A719CB6020000250002910A@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-performance
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.
 
All of this is on a RAID 5 array with 5 drives using xfs with
noatime,nobarrier and a 256MB BBU controller.
 
-Kevin

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Subject: Re: PostgreSQL 8.4 performance tuning questions
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