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Re: Cache Hit Ratio from system views

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Date: Thu, 30 Aug 2007 12:16:29 -0700
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On Aug 28, 5:02 pm, "Bob Jones" <em..._at_me.not> wrote: [snipped]
> > Yet you still insist that the two ratios can be
> > compared 'all else being equal'. You haven't told us what, exactly,
> > that proves, except that you can calculate a ratio consistently.
> That proves BCHR is meaningful.

How, precisely, does it prove the BCHR meaningful? Let's say, for example, your precious BCHR is sitting at a comfortable 97% and, miracle of miracles, your database is performing admirably. An hour later your BCHR is STILL sitting at 97%, but now you have a line of users outside your door complaining the database isn't responding. Your BCHR is at a lovely 97% so everything must be fine, no? No, even though nothing in the database configuration has changed (your 'all things being equal' noise). Tell us what this BCHR is telling you to do to fix this issue? Absolutely nothing. Something changed (possibly a user running some one-off query bringing the database to its knees, possibly something else) but the BCHR can't show you WHAT changed. In fact it didn't even BUDGE from its original value of 97%. It was flashing 'green' an hour ago, and it's flashing 'green' now, but something is amiss and it can't tell you what.

> It is ironic we are debating about something
> many consider meaningless.

Apparently all except you consider it meaningless.

> Do you ever adjust the buffer cache size?

Rarely, and only when it's actually necessary.

> What do you use as reference?

Wait statistics, usually. The BCHR doesn't enter into that discussion for what I consider good reasons which have already been listed in this thread.


David Fitzjarrell Received on Thu Aug 30 2007 - 14:16:29 CDT

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