Jeff V. Merkey writes:
> Also, Van mentioned the issue with double-caching. Since Oracle uses
> it's own cache, the current buffer cache implementation in Linux for
> O_SYNC obsolutley sucks for Oracle, since we will always be double
> buffering data. I mentioned to Alan having a directFS layer in Linux,
> where Oracle could talk to files in a way that would completely by-pass
> the Linux buffer cache. Given the current state of Linux and the file
> systems, this may be very difficult to support.
What about the raw-io support? If you are using a filesystem, you have
to live with how a filesystem works. If you really need direct device
access, you can use raw device access, raw-io (to avoid buffering) and
LVM (to avoid the partition nightmare).
Dan Kegel writes:
> Say, I thought Oracle could use raw disk access instead
> of going through the filesystem. Is O_SYNC used only
> when in a 'convenience development mode' where you are
> using the filesystem, before you go to the trouble of
> giving Oracle a whole raw partition?
Some people run with databases in files, but that is for people who don't
care about performance, IMHO. Double cache is one performance problem,
but there is also overhead from the filesystem itself (e.g. indirect block
lookups, atimes, no guarantee of linear file allocation in filesystem, etc).
Raw partitions are the only way to go, but really need LVM and raw-io in
order to make this useful.
Cheers, Andreas
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