Re: O_DIRECT use

Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> Tom Lane wrote:
>> Why exactly would we wish to minimize OS caching?

> 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.

Yeah, but people normally try to set things up to avoid doing large
sequential scans, at least in all the contexts where they need high
performance. For index searches you definitely want all the caching
you can get.

For that matter, I would expect that O_DIRECT also defeats readahead,
so I'd fully expect it to be a loser for seqscans too.

regards, tom lane