Re: 8.4 open item: copy performance regression?

Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes:
> I was going to say that since we flush the WAL every 16MB anyway (at 
> every XLOG file switch), you shouldn't see any benefit with larger ring 
> buffers, since to fill 16MB of data you're not going to write more than 
> 16MB WAL.

I'm not convinced that WAL segment boundaries are particularly relevant
to this.  The unit of flushing is an 8K page, not a segment.

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?
        regards, tom lane