Re: Anything new from IOUG? + "OWI" Born!! (Anjo/Mogens, please n

Did anyone at IOUG-A mention the two biggest jokes about The Buffer Cache Hit Ratio ?

First that there are lots of buffer accesses that Oracle doesn't record in the statistics it gives you; and secondly that there are lots of buffer accesses that it does tell you about that have not yet been included in any of the formulae that I've ever seen.

The former can be seen quite clearly through a couple of controlled experiments where you match logical I/O against CBC latch gets.

The second arises because the 'buffer is pinned' is a count of buffer visits through a 'short-cut'; and the value never gets mentioned.

I would also like to point out that not all 'hit ratios' are bad. The FAN hit ratio is a very useful indicator. (see http://miracleas.dk/undskyld/fhr.pdf in the short term for further details).

Jonathan Lewis
http://www.jlcomp.demon.co.uk

Author of:
Practical Oracle 8i: Building Efficient Databases

Next Seminar - Australia - July/August
http://www.jlcomp.demon.co.uk/seminar.html

Host to The Co-Operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.html

-----Original Message-----
To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Date: 23 April 2002 04:24
please n

|>
|> Somebody (I think it was Cary) mentioned your little PL/SQL
procedure that
|> will provide any required CHR. So you are famous, even if you were
not
|> present :)
|>

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