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Date: Sat, 14 Jul 2001 01:49:36 +1000
From: Andrew Morton <andrewm@uow.edu.au>
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To: "Jeffrey W. Baker" <jwbaker@acm.org>
CC: Lance Larsh <llarsh@oracle.com>,
        Brian Strand <bstrand@switchmanagement.com>,
        Andrea Arcangeli <andrea@suse.de>, linux-kernel@vger.kernel.org
Subject: Re: 2x Oracle slowdown from 2.2.16 to 2.4.4
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"Jeffrey W. Baker" wrote:
> 
> > ...
> > ext2: Throughput 2.71849 MB/sec (NB=3.39812 MB/sec  27.1849 MBit/sec)
> > ext3: Throughput 12.3623 MB/sec (NB=15.4529 MB/sec  123.623 MBit/sec)
> >
> > ext3 patches are at http://www.uow.edu.au/~andrewm/linux/ext3/
> >
> > The difference will be less dramatic with large, individual writes.
> 
> This is a totally transient effect, right?  The journal acts as a faster
> buffer, but if programs are writing a lot of data to the disk for a very
> long time, the throughput will eventually be throttled by writing the
> journal back into the filesystem.

It varies a lot with workload.  With large writes such as 
'iozone -s 300m -a -i 0' it seems about the same throughput
as ext2.  It would take some time to characterise fully.

> For programs that write in bursts, it looks like a huge win!

yes - lots of short writes (eg: mailspools) will benefit considerably.
The benefits come from the additional merging and sorting which
can be performed on the writeback data.

I suspect some of the dbench benefit comes from the fact that
the files are unlinked at the end of the test - if the data hasn't
been written back at that time the buffers are hunted down and
zapped - they *never* get written.

If anyone wants to test sync throughput, please be sure to use
0.9.3-pre - it fixes some rather sucky behaviour with large journals.

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