Re: checkpointer continuous flushing

On Wed, Jan 20, 2016 at 9:07 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> On 2016-01-20 12:16:24 -0300, Alvaro Herrera wrote:
> > Andres Freund wrote:
> >
> > > The relevant thread is at
> > >
http://archives.postgresql.org/message-id/CA%2BTgmoaCr3kDPafK5ygYDA9mF9zhObGp_13q0XwkEWsScw6h%3Dw%40mail.gmail.com
> > > what I didn't remember is that I voiced concern back then about
exactly this:
> > >
http://archives.postgresql.org/message-id/201112011518.29964.andres%40anarazel.de
> > > ;)
> >
> > Interesting. If we consider for a minute that part of the cause for the
> > slowdown is slowness in pg_clog, maybe we should reconsider the initial
> > decision to flush as quickly as possible (i.e. adopt a strategy where
> > walwriter sleeps a bit between two flushes) in light of the group-update
> > feature for CLOG being proposed by Amit Kapila in another thread -- it
> > seems that these things might go hand-in-hand.
>
> I don't think it's strongly related - the contention here is on read
> access to the clog, not on write access.

Aren't reads on clog contended with parallel writes to clog?

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com