Re: What is WAL used for?

Cott Lang wrote:

> On Fri, 2003-12-05 at 02:40, Thierry Missimilly wrote:
>
> > With the data=writeback mode, I increase the TPS by 18% and dicrease the wait
> > I/O from 54% to 30%.
> > I did not change my filesystem to ext2 as I have to have to cancel the partition
> > and recreate all the database. Futhermore, i have understood that journaled
> > filesystem allowed better and faster fsck after a Power off crash and it is not
> > redundant with the WAL Crash recovery.
> > I think that "journaling" is at file system level and WAL is above in the
> > Database level. What happen if the xlog filesystem has been breakdown by a power
> > off. All the Data concisentcy done by PG will be lost. I hope that data stored
> > in the FS journal, can avoid that.
>
> What's the recommended method of changing an ext3 partition to
> data=writeback mode on RH9?
>

For exemple, with the root privilege :
mount -t ext3 -o data=writeback /dev/sdb1 /data1

or in /etc/fstab :
/dev/sdb1 /data1 ext3 data=writeback 0 0

>
> I tried the tune2fs -j method to set the default journal type and
> rebooted, but saw *no* performance differences, so I was wondering if
> setting the default actually put it in writeback mode.
>
> Does anyone know if there's an easy way to verify the mode, or if I'm
> setting it wrong ?
>

By default the mode is "ordered".
The command : mount returns how FS are mounted.

Thierry Missimilly

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