Re: Quad Opteron stuck in the mud

On Thu, Jul 14, 2005 at 12:28:05AM -0600, Dan Harris wrote:

> Ok, so I remounted this drive as ext2 shortly before sending my first
> email today. It wasn't enough time for me to notice the ABSOLUTELY
> HUGE difference in performance change. Ext3 must really be crappy
> for postgres, or at least is on this box. Now that it's ext2, this
> thing is flying like never before. My CPU utilization has
> skyrocketed, telling me that the disk IO was constraining it immensely.

Were you using the default journal settings for ext3?

An interesting experiment would be to use the other journal options
(particularly data=writeback). From the mount manpage:

data=journal / data=ordered / data=writeback
Specifies the journalling mode for file data. Metadata is
always journaled. To use modes other than ordered on the root
file system, pass the mode to the kernel as boot parameter, e.g.
rootflags=data=journal.

journal
All data is committed into the journal prior to being
written into the main file system.

ordered
This is the default mode. All data is forced directly
out to the main file system prior to its metadata being
committed to the journal.

writeback
Data ordering is not preserved - data may be written into
the main file system after its metadata has been commit-
ted to the journal. This is rumoured to be the highest-
throughput option. It guarantees internal file system
integrity, however it can allow old data to appear in
files after a crash and journal recovery.

--
Alvaro Herrera (<alvherre[a]alvh.no-ip.org>)
Officer Krupke, what are we to do?
Gee, officer Krupke, Krup you! (West Side Story, "Gee, Officer Krupke")