Re: PostgreSQL 8.4 performance tuning questions

Tom Lane <tgl@sss.pgh.pa.us> wrote:
> "Kevin Grittner" <Kevin.Grittner@wicourts.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