Re: moving pg_xlog -- yeah, it's worth it!

Kevin Grittner wrote:
> I wonder if it might also pay to make the background writer even more
> aggressive than we have, so that SELECT-only queries don't spend so
> much time writing pages.
You can easily quantify if the BGW is aggressive enough.  Buffers leave
the cache three ways, and they each show up as separate counts in
pg_stat_bgwriter:  buffers_checkpoint, buffers_clean (the BGW), and
buffers_backend (the queries).  Cranking it up further tends to shift
writes out of buffers_backend, which are the ones you want to avoid,
toward buffers_clean instead.  If buffers_backend is already low on a
percentage basis compared to the other two, there's little benefit in
trying to make the BGW do more.

--
Greg Smith    2ndQuadrant   Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com  www.2ndQuadrant.com