Re: Cache Hit Ratio from system views

From: Richard Foote <richard.foote_at_nospam.bigpond.com>
Date: Wed, 22 Aug 2007 13:37:02 GMT
Message-ID: <2_Wyi.24466$4A1.1328@news-server.bigpond.net.au>

"Bob Jones" <email_at_me.not> wrote in message news:kOtyi.50198$YL5.8637_at_newssvr29.news.prodigy.net...

> High BCHR is always better than low - provided everything else being
> equal. If BCHR is useless for the stated reasons, no other indicator would
> be useful.

This I'm afraid is where you're fundamentally incorrect.

A high BCHR can mean your database is on life support, struggling to cope with exessive LIOs due to inefficient SQL with users staring at an hourglass rather than returned data.

A BCHR that has increased can mean your database has suddenly hit significant performance issues. Or it can mean things have improved. Or it can mean response times remain unaffected.

A BCHR that has reduced can mean your database has suddenly hit significant performance issues. Or it can mean things have improved (yes, improved because that crippling transaction that was previously performing poorly due to massively exessive LIOs has been fixed, reducing the overall BCHR) . Or it can mean response times remain unaffected.

Not much of an indicator is it ?

But saying that a BCHR is *always* better than a low is just plain wrong wrong wrong ...

Do yourself a favour and read this
www.hotsos.com/e-library/abstract.php?id=6 ?

Cheers

Richard Received on Wed Aug 22 2007 - 08:37:02 CDT