wal_synch_method = open_sync safe on RHEL 5.5?

From: Mark Kirkwood
Subject: wal_synch_method = open_sync safe on RHEL 5.5?
Date: ,
Msg-id: 4C1ACE5F.1080802@catalyst.net.nz
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Responses: Re: wal_synch_method = open_sync safe on RHEL 5.5?  (Greg Smith)
List: pgsql-performance

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wal_synch_method = open_sync safe on RHEL 5.5?  (Mark Kirkwood, )
 Re: wal_synch_method = open_sync safe on RHEL 5.5?  (Greg Smith, )
  Re: wal_synch_method = open_sync safe on RHEL 5.5?  (Mark Mielke, )
   Re: wal_synch_method = open_sync safe on RHEL 5.5?  (Greg Smith, )
  Re: wal_synch_method = open_sync safe on RHEL 5.5?  (Mark Kirkwood, )

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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From: Mark Kirkwood
Date:
Subject: Re: wal_synch_method = open_sync safe on RHEL 5.5?
From: Greg Smith
Date:
Subject: Re: wal_synch_method = open_sync safe on RHEL 5.5?