Re: Major Linux performance regression; shouldn't we be worried about RHEL6?

> The main change here was discussed back in January:
> http://archives.postgresql.org/message-id/4B512D0D.4030909@2ndquadrant.com
>
> What I've been doing about this is the writing leading up to
> http://wiki.postgresql.org/wiki/Reliable_Writes so that when RHEL6 does
> ship, we have a place to point people toward that makes it better
> documented that the main difference here is a reliability improvement
> rather than a performance regression.  I'm not sure what else we can do
> here, other than organizing more testing for kernel bugs in this area on
> RHEL6.  The only way to regain the majority of the "lost" performance
> here is to turn off synchronous_commit in the default config.

Yeah, I was looking at that.  However, there seems to be some
indications that there was a drop in performance specifically in 2.6.32
which went beyond fixing the reliability:

http://www.phoronix.com/scan.php?page=article&item=linux_2636_btrfs&num=1

However, Phoronix doesn't say what sync option they're using; quite
likely it's O_DSYNC.  Unfortunately, the fact that users now need to be
aware of the fsync_method again, after having it set automatically for
them for the last 4 years, is a usability regression for *us*.  Anything
that's reasonable for us to do about it?

--
                                  -- Josh Berkus
                                     PostgreSQL Experts Inc.
                                     http://www.pgexperts.com