wal_synch_method = open_sync safe on RHEL 5.5? - Mailing list pgsql-performance

From Mark Kirkwood
Subject wal_synch_method = open_sync safe on RHEL 5.5?
Date
Msg-id 4C1ACE5F.1080802@catalyst.net.nz
Whole thread Raw
Responses Re: wal_synch_method = open_sync safe on RHEL 5.5?  (Greg Smith <greg@2ndquadrant.com>)
List 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.

pgsql-performance by date:

Previous
From: Tom Wilcox
Date:
Subject: Re: requested shared memory size overflows size_t
Next
From: Greg Smith
Date:
Subject: Re: wal_synch_method = open_sync safe on RHEL 5.5?