[z/OS] Group Buffer Pool Sizing

Hugh Lapham

[z/OS] Group Buffer Pool Sizing
I'm looking at SMF data to evaluate our GBP layout and have some
confusing data I'm trying to figure out. If anyone can enlighten me,
I'd be very happy.

I'm finding values like this (this was a full day's data):
QBGAGNSYSTEMSSIDQBGAGGQBGASWQBGAXDQBGAXR14ZOS2DB2B81,24320713111,102
ZOS3DB2C80,5992111236,099
What I don't understand is how, if I have such a small volume of
updates, I have such a huge volume of misses. My understanding was that
every page update causes a CF Write (QBGASW) and the cross-invalidation
of the page in the other DB2 subsystem(s). A subsequent GetPage in the
other subsystem(s) would result in a CF Read for the cross-invalidated
page which would either succeed (QBGAXD) or fail (QBGAXR) but in either
case would result in a valid page in the local buffer pool until there
were additional updates.

This particular GBP is sized at 8M which I thought would be more than
adequate to manage the indicated update volume.

What am I missing? and thanks in advance ;-))

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Joel Goldstein

Re: [z/OS] Group Buffer Pool Sizing
(in response to Hugh Lapham)
How do you know that any given page you update has cross system interest/residency at that point in time?
What are the definitions for your group pool(s) - directory entries vs. data pages?

Regards,
Joel

Joel Goldstein
Responsive Systems
Buffer Pool Tool for DB2, the worldwide industry standard
Performance software that works......
Predicts Group Buffer Pool performance too!
www.responsivesystems.com
(732) 972-1261
----- Original Message -----
From: Hugh Lapham
Newsgroups: bit.listserv.db2-l
To: [login to unmask email]
Sent: Thursday, December 07, 2006 10:55 AM
Subject: [DB2-L] [z/OS] Group Buffer Pool Sizing


I'm looking at SMF data to evaluate our GBP layout and have some confusing data I'm trying to figure out. If anyone can enlighten me, I'd be very happy.

I'm finding values like this (this was a full day's data):
QBGAGN
SYSTEM
SSID
QBGAGG
QBGASW
QBGAXD
QBGAXR

14
ZOS2
DB2B
81,243
207
131
11,102


ZOS3
DB2C
80,599
211
123
6,099


What I don't understand is how, if I have such a small volume of updates, I have such a huge volume of misses. My understanding was that every page update causes a CF Write (QBGASW) and the cross-invalidation of the page in the other DB2 subsystem(s). A subsequent GetPage in the other subsystem(s) would result in a CF Read for the cross-invalidated page which would either succeed (QBGAXD) or fail (QBGAXR) but in either case would result in a valid page in the local buffer pool until there were additional updates.

This particular GBP is sized at 8M which I thought would be more than adequate to manage the indicated update volume.

What am I missing? and thanks in advance ;-))
--------------------------------------------------------------------------------- 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

---------------------------------------------------------------------------------
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