Re: PostgreSQL 8.4 performance tuning questions

On 7/30/09 11:24 AM, "Stefan Kaltenbrunner" <stefan(at)kaltenbrunner(dot)cc> wrote:

> 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.
>

That's not an option when a dump compressed is 200GB and uncompressed is
1.3TB, for example.

>
> Stefan
>
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