Jeff wrote:
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.
all my numbers are with -Z0 and it is the backend (COPY and/or index
creation) that is the limit. If you start using compression you are
shifting the load to pg_dump.
Stefan
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