pg.ddx.io  pgsql-performance@postgresql.org mailing list archive  

help / color / mirror / Atom feed
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alexander Staubo <alex@purefiction.net>
Cc: Michael Stone <mstone+postgres@mathom.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: New to PostgreSQL, performance considerations
Date: Tue, 12 Dec 2006 10:47:42 -0500
Message-ID: <3356.1165938462@sss.pgh.pa.us> (raw)
In-Reply-To: <42B14BCF-B745-4F94-B5EA-97997744A4D5@purefiction.net>
References: <8a0c7af10612110531sbb019ck259fb16d131fdb50@mail.gmail.com>
	<60psaq5t94.fsf@dba2.int.libertyrms.com>
	<E1GtolA-0008Fk-4R@elasmtp-banded.atl.sa.earthlink.net>
	<20061211173105.GH16692@mathom.us>
	<E1Gtplp-0004Ka-GM@elasmtp-junco.atl.sa.earthlink.net>
	<20061211184726.GI16692@mathom.us>
	<E1GtrB8-0005rw-Iu@elasmtp-kukur.atl.sa.earthlink.net>
	<457DA782.3060506@modgraph-usa.com>
	<8a0c7af10612111422x6bdcc0c2p7cbfeb5a7b0e0374@mail.gmail.com>
	<2FC0D8E7-F8ED-452F-BB13-FB665B516E7F@purefiction.net>
	<20061212123252.GR16692@mathom.us>
	<42B14BCF-B745-4F94-B5EA-97997744A4D5@purefiction.net>

Alexander Staubo <alex@purefiction.net> writes:
> No, fsync=on. The tps values are similarly unstable with fsync=off,  
> though -- I'm seeing bursts of high tps values followed by low-tps  
> valleys, a kind of staccato flow indicative of a write caching being  
> filled up and flushed.

It's notoriously hard to get repeatable numbers out of pgbench :-(

A couple of tips:
	* don't put any faith in short runs.  I usually use -t 1000
	  plus -c whatever.
	* make sure you loaded the database (pgbench -i) with a scale
	  factor (-s) at least equal to the maximum -c you want to test.
	  Otherwise you're mostly measuring update contention.
	* pay attention to when checkpoints occur.  You probably need
	  to increase checkpoint_segments if you want pgbench not to be
	  checkpoint-bound.

			regards, tom lane



view thread (124+ messages)  latest in thread

Message-ID: <3356.1165938462@sss.pgh.pa.us>
Permalink:  ../3356.1165938462@sss.pgh.pa.us/
Also on:    postgresql.org/message-id/3356.1165938462@sss.pgh.pa.us

 · 

reply
Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: pgsql-performance@postgresql.org
  Cc: tgl@sss.pgh.pa.us, alex@purefiction.net, mstone+postgres@mathom.us
  Subject: Re: New to PostgreSQL, performance considerations
  In-Reply-To: <3356.1165938462@sss.pgh.pa.us>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox