Re: 8.4 open item: copy performance regression?

"Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes:
> Tom Lane <tgl@sss.pgh.pa.us> wrote: 
>> I wonder though whether the wal_buffers setting interacts with the
>> ring size.  Has everyone who's tested this used the same 16MB
>> wal_buffers setting as in Alan's original scenario?
> I had been using his postgresql.conf file, then added autovacuum =
> off.  When I tried with setting the ring size to 16MB, I accidentally
> left off the step to copy the postgresql.conf file, and got better
> performance.

Huh, that's bizarre.  I can see that increasing shared_buffers should
make no difference in this test case (we're not using them all anyway).
But why should increasing wal_buffers make it slower?  I forget the
walwriter's control algorithm at the moment ... maybe it works harder
when wal buffers are full?

BTW, I committed the change to use 16MB; that will be in RC2.
        regards, tom lane