Re: Parallel pg_dump for 9.1

On Mar 30, 2010, at 8:15 AM, Stefan Kaltenbrunner wrote:

> Peter Eisentraut wrote:
>> On tis, 2010-03-30 at 08:39 +0200, Stefan Kaltenbrunner wrote:
>>> on fast systems pg_dump is completely CPU bottlenecked
>> Might be useful to profile why that is. I don't think pg_dump has
>> historically been developed with CPU efficiency in mind.
>
> It's not pg_dump that is the problem - it is COPY that is the limit.
> In my specific case als the fact that a lot of the columns are bytea
> adds to the horrible CPU overhead (fixed in 9.0). Still our bulk
> load & unload performance is still way slower on a per core
> comparision than a lot of other databases :(
>

Don't forget the zlib compression used in -Fc (unless you use -Z0)
takes a fair amount of cpu too.
I did some tests and it turned out that -Z0 actually took longer than -
Z1 simply because there was a lot more data to write out, thus I
became IO bound not CPU bound.

There's a thing called pigz around that is a parallel gzip
implementation - wonder how much of that could be adapted to pg_dumps
use as compression does use a considerable amount of time (even at -
Z1). The biggest problem I can immediately see is that it uses threads.

--
Jeff Trout <jeff(at)jefftrout(dot)com>
http://www.stuarthamm.net/
http://www.dellsmartexitin.com/