Re: lock contention on parallel COPY ?

On Fri, 2008-09-26 at 12:38 -0400, Tom Lane wrote:
> Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc> writes:
> > heh no log archiving - I actually said that I'm now playing with
> > --truncate-before-load which seems to cause a noticeable performance (as
> > in IO generated) increase but I still see >130000 context switches/s and
> > a profile that looks like:
>
> > samples % symbol name
> > 55526 16.5614 LWLockAcquire
> > 29721 8.8647 DoCopy
> > 26581 7.9281 CopyReadLine
> > 25105 7.4879 LWLockRelease
> > 15743 4.6956 PinBuffer
> > 14725 4.3919 heap_formtuple
>
> Still a lot of contention for something, then. You might try turning on
> LWLOCK_STATS (this only requires recompiling storage/lmgr/lwlock.c) to
> get some evidence about what.

Probably loading a table with a generated PK or loading data in
ascending sequence, so its contending heavily for the rightmost edge of
the index.

We need to load data a block at a time and buffer the inserts into the
index also, so we don't need to lock/unlock per row.

--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support