Re: oracle benchmarks on VMS

"Hein van den Heuvel" <hein_netscape_at_eps.zko.dec.com> wrote in message news:3E63C5E9.88569D3F_at_eps.zko.dec.com...

...

> On Unix systems the OS tends to waste time and memory buffering Oracle
> data pages which are better managerd by Oracle in its buffer pool (SGA).
> On many Unix implementation, for ultimate Oracle perfromance once has to
> deal with hard-to-manage 'Raw Devices' to avoid said buffering.

Not on the most common Unixes. Veritas' VxFS file system supports direct (unbuffered) file I/O, and it's available pretty widely (it may even be the standard file system on HP-UX - they had their fingers in some part of the HP-UX data management pie, anyway). VxFS runs on Solaris, and IIRC Sun's own file system also supports direct I/O (not too surprising, given how important Oracle is to them). Linux has some form of direct I/O in 2.4, though it may be scheduled for more massaging to eliminate some kludgery. VxFS was recently ported to AIX (I don't know whether their native JFS supports direct I/O, though).

(Many Unixes support asynchronous I/O too, but AFAIK none as well as VMS: they - and the POSIX asynchrony model - never seemed to understand how completion processing should work.)

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