On Wed, Apr 7, 2010 at 7:06 PM, Craig James <craig_james@xxxxxxxxxxxxxx> wrote: > On 4/7/10 5:47 PM, Robert Haas wrote: >> On Wed, Apr 7, 2010 at 6:56 PM, David Rees<drees76@xxxxxxxxx> wrote: >>>> synchronous_commit = off >>> >>> You are playing with fire here. You should never turn this off unless >>> you do not care if your data becomes irrecoverably corrupted. >> >> That is not correct. Turning off synchronous_commit is sensible if >> you don't mind losing the last few transactions on a crash. What will >> corrupt your database is if you turn off fsync. Whoops, you're right. > A bit off the original topic, but ... > > I set it this way because I was advised that with a battery-backed RAID > controller, this was a safe setting. Is that not the case? Robert has it right - with synchronous_commit off, your database will always be consistent, but you may lose transactions in the event of a crash. Doesn't matter if you have a BBU or not - all the BBU does is give the controller the ability to acknowledge a write without the data actually having been written to disk. According to the documentation, with synchronous_commit off and a default wal_writer_delay of 200ms, it's possible to lose up to a maximum of 600ms of data you thought were written to disk. -Dave -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
