Skip site navigation (1) Skip section navigation (2)

Re: Initial 9.2 pgbench write results

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Ants Aasma <ants(dot)aasma(at)eesti(dot)ee>
Cc: Greg Smith <greg(at)2ndquadrant(dot)com>, simon(at)2ndquadrant(dot)com, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Initial 9.2 pgbench write results
Date: 2012-02-28 16:46:39
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Tue, Feb 28, 2012 at 1:15 AM, Ants Aasma <ants(dot)aasma(at)eesti(dot)ee> wrote:
> My hypothesis for the TPS regression is that it is due to write combining.
> When the workload is mainly bound by I/O, every little bit that can be saved
> helps the bottomline. Larger scalefactors don't get the benefit because
> there is less write combining going on overall.

This is an interesting hypothesis which I think we can test.  I'm
thinking of writing a quick patch (just for testing, not for commit)
to set a new buffer flag BM_BGWRITER_CLEANED to every buffer the
background writer cleans.   Then we can keep a count of how often such
buffers are dirtied before they're evicted, vs. how often they're
evicted before they're dirtied.  If any significant percentage of them
are redirtied before they're evicted, that would confirm this
hypothesis.  At any rate I think the numbers would be interesting to

Robert Haas
The Enterprise PostgreSQL Company

In response to


pgsql-hackers by date

Next:From: karavelovDate: 2012-02-28 16:47:49
Subject: Re: swapcache-style cache?
Previous:From: Greg SmithDate: 2012-02-28 16:40:29
Subject: Re: Hot Standby Failover Scenario

Privacy Policy | About PostgreSQL
Copyright © 1996-2017 The PostgreSQL Global Development Group