basic bp hit ratio question

Bill Brown

basic bp hit ratio question
i was just going through the process of calculating the bufferbppo hit ratio
on new bp and came across a very simple question. i compute my io by adding
up the randon io, sequential io, seq prefetch io, list prefetch io, and
dynamic prefetch io. i then started calculating my total get pages. i
addid in my randon and seq getpages and then i came upon my question.

when adding in the prefetch getpage counts do i use the "requests" or the
"pages read" counts?

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Joel Goldstein

Re: basic bp hit ratio question
(in response to Bill Brown)
Bill,

The System Hit Ratio formula is:
(GP-SumOfAllPagesRead)/Getpages

While we've all used hit ratios for ever, the metric you really want to
track is the I/O rate/Sec.
This is measurable and convertible into CPU Secs, and application
delay/elapsed times.

See my article and presentation: The Buffer Pool Hit Ratio is Dead! on
www.responsivesystems.com

Regards,
Joel

----- Original Message -----
From: "Bill Brown" <[login to unmask email]>
Newsgroups: bit.listserv.db2-l
To: <[login to unmask email]>
Sent: Wednesday, December 29, 2004 8:12 AM
Subject: [DB2-L] basic bp hit ratio question


>i was just going through the process of calculating the bufferbppo hit
>ratio
> on new bp and came across a very simple question. i compute my io by
> adding
> up the randon io, sequential io, seq prefetch io, list prefetch io, and
> dynamic prefetch io. i then started calculating my total get pages. i
> addid in my randon and seq getpages and then i came upon my question.
>
> when adding in the prefetch getpage counts do i use the "requests" or the
> "pages read" counts?
>
> ---------------------------------------------------------------------------------
> Welcome to the IDUG DB2-L list. To unsubscribe, go to the archives and
> home page at http://www.idugdb2-l.org/archives/db2-l.html. From that page
> select "Join or Leave the list". The IDUG DB2-L FAQ is at
> http://www.idugdb2-l.org. The IDUG List Admins can be reached at
> [login to unmask email] Find out the latest on IDUG conferences
> at http://conferences.idug.org/index.cfm
>
>

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Venkat Srinivasan

Re: basic bp hit ratio question
(in response to Joel Goldstein)
Aside from what Joel said, you cannot use I/O counts and getpages in the
same equation.
The formula should compare pages read due to alll access types Vs total
Getpages and not i/os done due to all pages Vs getpages.
Venkat

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