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Message-ID: <4C1ACE5F.1080802@catalyst.net.nz>
Date: Fri, 18 Jun 2010 13:39:43 +1200
From: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
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To: pgsql-performance@postgresql.org
Subject: wal_synch_method = open_sync safe on RHEL 5.5?
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Some more on the RHEL 5.5 system I'm helping to setup. Some benchmarking 
using pgbench appeared to suggest that wal_sync_method=open_sync was a 
little faster than fdatasync [1]. Now I recall some discussion about 
this enabling direct io and the general flakiness of this on Linux, so 
is the option regarded as safe?

[1] The workout:

$ pgbench -i -s 1000 bench
$ pgbench -c [1,2,4,8,32,64,128] -t 10000

Performance peaked around 2500 tps @32 clients using open_sync and 2200 
with fdatasync. However the disk arrays are on a SAN and I suspect that 
when testing with fdatasync later in the day there may have been 
workload 'leakage' from other hosts hitting the SAN.

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<font size="-1"><font face="Helvetica">Some more on the RHEL 5.5 system
I'm helping to setup. Some benchmarking using pgbench appeared to
suggest that wal_sync_method=open_sync was a little faster than
fdatasync [1]. Now I recall some discussion about this enabling direct
io and the general flakiness of this on Linux, so is the option
regarded as safe?<br>
<br>
[1] The workout: <br>
<br>
$ pgbench -i -s 1000 bench<br>
$ pgbench -c [1,2,4,8,32,64,128] -t 10000<br>
<br>
Performance peaked around 2500 tps @32 clients using open_sync and 2200
with fdatasync. However the disk arrays are on a SAN and I suspect that
when testing with fdatasync later in the day there may have been
workload 'leakage' from other hosts hitting the SAN.<br>
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</body>
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