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wal_synch_method = open_sync safe on RHEL 5.5?

From: Mark Kirkwood <mark(dot)kirkwood(at)catalyst(dot)net(dot)nz>
To: pgsql-performance(at)postgresql(dot)org
Subject: wal_synch_method = open_sync safe on RHEL 5.5?
Date: 2010-06-18 01:39:43
Message-ID: 4C1ACE5F.1080802@catalyst.net.nz (view raw or flat)
Thread:
Lists: pgsql-performance
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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Next:From: Greg SmithDate: 2010-06-18 03:29:36
Subject: Re: wal_synch_method = open_sync safe on RHEL 5.5?
Previous:From: Tom WilcoxDate: 2010-06-17 23:46:11
Subject: Re: requested shared memory size overflows size_t

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