Subject: Re: [HACKERS] no universally correct setting for fsync

From: "Kevin Grittner" <[email-masked]>
Date: Sat, 08 May 2010 08:09:51 -0500

Josh Berkus  wrote:
 
> I believe that the note about needing fsync for Warm Standby to
> work correctly is true, but could someone verify it?
 
It couldn't really affect the archiving of the WAL files, but if your
warm standby is there for recovery purposes, it might not make a lot
of sense to turn off fsync on the standby -- if that is something
which has an effect during the recovery phase.  Does it?
 
Also, perhaps the issue deserves some mention in the PITR recovery
section:
 
http://www.postgresql.org/docs/9.0/static/continuous-archiving.html#BACKUP-PITR-RECOVERY
 
Step 6 says:
 
| If you have unarchived WAL segment files that you saved in step 2,
| copy them into pg_xlog/. (It is best to copy them, not move them,
| so you still have the unmodified files if a problem occurs and you
| have to start over.)

If the recovery is happening because of OS or hardware failure on the
source, and it was running with fsync off, this might be unwise.
 
-Kevin