Re: hanging for 30sec when checkpointing

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
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  Email: gspiegelberg@Cranel.com
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