Re: O_DIRECT in freebsd

On Wed, Jun 18, 2003 at 10:01:37AM +1000, Gavin Sherry wrote:
> On Tue, 17 Jun 2003, Tom Lane wrote:
> > * Consider use of open/fcntl(O_DIRECT) to minimize OS caching
> >
> > I personally disagree with this TODO item for the same reason Sean
> > cited: Postgres is designed and tuned to rely on OS-level disk caching,
> > and bypassing that cache is far more likely to hurt our performance than
> > help it.
>
> DB2 and Oracle, from memory, allow users to pass hints to the planner to
> use/not use file system caching. This could be useful if you had an
> application retrieving a large amount of data on an adhoc basis. The large
> retrieval would empty out the disk cache there by negatively impacting
> upon other applications operating on data which should be cached.

Might it make sense to do this for on-disk sorts, since sort_mem is
essentially being used as a disk cache (at least for reads)?
--
Jim C. Nasby (aka Decibel!) jim(at)nasby(dot)net
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