From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Manfred Spraul <manfred(at)colorfullife(dot)com>, pgsql-patches(at)postgresql(dot)org |
Subject: | Re: performance: use pread instead of lseek+read |
Date: | 2003-03-06 19:01:36 |
Message-ID: | 200303061901.h26J1a218765@candle.pha.pa.us |
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Lists: | pgsql-patches |
BSD/OS doesn't have pread either. Isn't pread() just a case of merging
two system calls into one? Does a single system call cause that much
overhead? I didn't think so.
Doesn't pread() do the lseek() internally anyway.
---------------------------------------------------------------------------
Tom Lane wrote:
> Manfred Spraul <manfred(at)colorfullife(dot)com> writes:
> > Do you know that empty lseeks foul up readahead recognition on some OS?
> > If yes, which OS? I've checked FreeBSD and Linux, they don't do it.
>
> Who knows? But it would be folly to extrapolate from those two
> datapoints to all the platforms we support.
>
> > - which benchmark would be interesting?
>
> Something that measures the performance "in context", that is as part of
> normal database activity, not just the syscall overhead. pgbench is
> notoriously hard to get reproducible numbers out of, but you could try
> it if you like.
>
> > - which OS did you use when you got 'no manpage for pread'?
>
> HPUX 10.20.
>
> regards, tom lane
>
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--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
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