Re: O_DIRECT use

Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > I have added this item to TODO:
> >     * Consider use of open/fctl(O_DIRECT) to minimize OS caching
> 
> Why exactly would we wish to minimize OS caching?
> 
> In my mind, Postgres has always relied heavily on the existence of a
> layer of kernel caching.  Disabling that will hurt far more than help.

Not sure. Someone on IRC brought it up.  If we are sequential scanning a
large table, caching may be bad because we are pushing out stuff already
in the cache that may be useful.  It is related to this TODO item:
* Add free-behind capability for large sequential scans (Bruce)

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