Re: performance: use pread instead of lseek+read

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
>
> ---------------------------(end of broadcast)---------------------------
> TIP 3: if posting/reading through Usenet, please send an appropriate
> subscribe-nomail command to majordomo(at)postgresql(dot)org so that your
> message can get through to the mailing list cleanly
>

--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073