Message-Id: <4BC70ADE0200002500030965@gw.wicourts.gov>
Date: Thu, 15 Apr 2010 12:47:26 -0500
From: "Kevin Grittner" <Kevin.Grittner@wicourts.gov>
To: "Marinos Yannikos" <mjy@geizhals.at>
Cc: "pgsql-performance" <pgsql-performance@postgresql.org>,
	"Tom Lane" <tgl@sss.pgh.pa.us>
Subject: Re: 8.3.9 - latency spikes with Linux (and tuning
	for consistently low latency)
References: <4BC742C8.2050301@geizhals.at><4BC742C8.2050301@geizhals.at>
	<4674.1271353080@sss.pgh.pa.us>
In-Reply-To: <4674.1271353080@sss.pgh.pa.us>
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Tom Lane <tgl@sss.pgh.pa.us> wrote:
 
> Have you checked whether the spikes correlate with checkpoints? 
> Turn on log_checkpoints and watch for awhile.  If so, fooling with
> the checkpoint parameters might give some relief.
 
If that by itself doesn't do it, I've found that making the
background writer more aggressive can help.  We've had good luck
with:
 
bgwriter_lru_maxpages = 1000
bgwriter_lru_multiplier = 4.0
 
If you still have checkpoint-related latency issues, you could try
scaling back shared_buffers, letting the OS cache handle more of the
data.
 
Also, if you have a RAID controller with a battery-backed RAM cache,
make sure it is configured for write-back.
 
-Kevin