2010/2/18 Fujii Masao <masao(dot)fujii(at)gmail(dot)com>:
> On Thu, Feb 18, 2010 at 7:04 PM, Heikki Linnakangas
> <heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
>> Magnus Hagander wrote:
>>> O_DIRECT helps us when we're not going to read the file again, because
>>> we don't waste cache on it. If we are, which is the case here, it
>>> should be really bad for performance, since we actually have to do a
>>> physical read.
>>> Incidentally, that should also apply to general WAL when archive_mdoe
>>> is on. Do we optimize for that?
>> Hmm, no we don't. We do take that into account so that we refrain from
>> issuing posix_fadvice(DONTNEED) if archive_mode is on, but we don't
>> disable O_DIRECT. Maybe we should..
> Since the performance of WAL write is more important than that of WAL
> archiving in general, that optimization might offer little benefit.
Well, it's going to make the process that reads the WAL cause actual
physical I/O... That'll take a chunk out of your total available I/O,
which is likely to push you to the limit of your I/O capacity much
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