| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Greg Stark <gsstark(at)mit(dot)edu> |
| Cc: | Alex Turner <armtuk(at)gmail(dot)com>, "Jim C(dot) Nasby" <decibel(at)decibel(dot)org>, William Yu <wyu(at)talisys(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: How to improve db performance with $7K? |
| Date: | 2005-04-07 04:14:57 |
| Message-ID: | 13449.1112847297@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
Greg Stark <gsstark(at)mit(dot)edu> writes:
> In any case the issue with the IDE protocol is that fundamentally you
> can only have a single command pending. SCSI can have many commands
> pending.
That's the bottom line: the SCSI protocol was designed (twenty years ago!)
to allow the drive to do physical I/O scheduling, because the CPU can
issue multiple commands before the drive has to report completion of the
first one. IDE isn't designed to do that. I understand that the latest
revisions to the IDE/ATA specs allow the drive to do this sort of thing,
but support for it is far from widespread.
regards, tom lane
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