scott.marlowe wrote:
On Wed, 4 Feb 2004, Iain wrote:
If I understand checkpoints correctly, data that is already written to the
WAL (and flushed to disk) is being written to the DB (flushing to disk).
Meanwhile, other writer transactions are continuing to busily write to the
WAL. In which case a disk bandwidth problem (other than kernal config
issues) may be helped by placing the WAL files on a disk (and maybe even
controller) seperate from the DB.
Also, running on SCSI drives will be much faster than running on IDE
drives if the IDE drives have their caches disabled like they should,
since they lie otherwise. Since SCSI disks don't usually lie, and are
designed to handle multiple requests in parallel, they are much faster as
parallel load increases. If you're writing a lot, you should either have
a great number of IDE drives with the write cache turned off, like some of
the newer storage devices made of ~100 IDE drives, or you should have
SCSI. SCSI's advantage won't be as great as the number of drives
approaches infinity. But for 1 to 10 drives my guess is that SCSI is
gonna be a clear winner under parallel load.
Don't forget the file system. Most journaling file systems are great
for reliability but aren't always so hot come performance and those
that are may require tweaking. Linux EXT3, IMO, works best when the
journal is kept on a different device and the file system is mounted
with the data=writeback option. Those 2 things in our test environment
were worth a speedup of close to 14%.
--
Greg Spiegelberg
Sr. Product Development Engineer
Cranel, Incorporated.
Phone: 614.318.4314
Fax: 614.431.8388
Email: [EMAIL PROTECTED]
Cranel. Technology. Integrity. Focus.
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