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@colorfullife.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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