Re: Buffer cache statistics (ratios) and CBO SQL optimization?

"Niall Litchfield" <n-litchfield_at_audit-commission.gov.uk> wrote:
>
> Elapsed times include waiting on following events:
> Event waited on Times Max. Wait Total
> Waited
> ----------------------------------------
> Waited ---------- ------------
> db file sequential read 160004 1.49
> 398.90
> db file scattered read 20732 0.43
> 86.62
>
> suggesting an *average* physical IO time for a single block read of
> 3989000/160004=25 milliseconds.

398.90 / 160004 = 0.00249 = 2.5 milliseconds, not 25 milliseconds.

>
> comments and clarifications welcome. The LIO figure seems reasonable to
> me and not wildly out of line with Jonathan's conjecture, the disk figure
> seems about twice as big as I would expect :(. None of this appears to
> bear out my 10-100 times figure, nor does it bear out the 14000 times
> figures I have also seen.

Xho

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