Re: checkpointer continuous flushing

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. While Amit's patch will reduce
the impact of that a bit, I don't see it making a fundamental
difference.

Andres