bufferpool "ifcid 6" inconsistent data

Larry Kirkpatrick

bufferpool "ifcid 6" inconsistent data
I have found out that the reason for the same page being read a second time
was that the first time the page was read was due to a "parallel" process.
When DB2 is reading via a parallel process, the page may be almost
immediately reused. This keeps a parallel process from stealing all the pages
from a bufferpool.54

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Richard Humphris

Re: bufferpool "ifcid 6" inconsistent data
(in response to Larry Kirkpatrick)
Very interesting; thanks for sharing this information with everyone.

Richard Humphris

-----Original Message-----
From: DB2 Data Base Discussion List [mailto:[login to unmask email] On
Behalf Of Larry
Sent: Thursday, January 03, 2008 3:15 PM
To: [login to unmask email]
Subject: Re: [DB2-L] bufferpool "ifcid 6" inconsistent data

I have found out that the reason for the same page being read a second
time
was that the first time the page was read was due to a "parallel"
process.
When DB2 is reading via a parallel process, the page may be almost
immediately reused. This keeps a parallel process from stealing all the
pages
from a bufferpool.54

The IDUG DB2-L Listserv is only part of your membership in IDUG. DB2-L
list archives, the FAQ, and delivery preferences are at
http://www.idug.org/lsidug under the Listserv tab. While at the site,
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Max Scarpa

Re: bufferpool "ifcid 6" inconsistent data
(in response to Richard Humphris)

That's correct as parallelism works (among other things) if the query is
read-only. Anyway there are some BP limits that are used by parallel
processes.

MAx Scarpa




Larry
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ORG> inconsistent data


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I have found out that the reason for the same page being read a second time

was that the first time the page was read was due to a "parallel" process.

When DB2 is reading via a parallel process, the page may be almost
immediately reused. This keeps a parallel process from stealing all the
pages
from a bufferpool.54

The IDUG DB2-L Listserv is only part of your membership in IDUG. DB2-L
list archives, the FAQ, and delivery preferences are at
http://www.idug.org/lsidug under the Listserv tab. While at the site, you
can also access the IDUG Online Learning Center, Tech Library and Code
Place, see the latest IDUG conference information, and much more. If you
have not yet signed up for Basic Membership in IDUG, available at no cost,
click on Member Services at http://www.idug.org/lsms

The IDUG DB2-L Listserv is only part of your membership in IDUG. DB2-L list archives, the FAQ, and delivery preferences are at http://www.idug.org/lsidug under the Listserv tab. While at the site, you can also access the IDUG Online Learning Center, Tech Library and Code Place, see the latest IDUG conference information, and much more. If you have not yet signed up for Basic Membership in IDUG, available at no cost, click on Member Services at http://www.idug.org/lsms

Joel Goldstein

Re: bufferpool "ifcid 6" inconsistent data
(in response to Max Scarpa)
There's another major consideration with parallel processes.

The vppseqt % is applied to the vpseqt %.
If you have 1,000 buffers, and vpseqt=80, and vppseqt=50, the number of
buffers available to parallel SP access is 400.
So the pages fall off the sequential Q much faster.

I'm not aware that parallel processing uses an MRU technique instead of the
std LRU. Some utilities use MRU.
Is this what you think it is doing?

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
tel. (732) 972-1261
fax.(732) 972-9416
----- Original Message -----
From: "Larry" <[login to unmask email]>
Newsgroups: bit.listserv.db2-l
To: <[login to unmask email]>
Sent: Thursday, January 03, 2008 4:15 PM
Subject: Re: [DB2-L] bufferpool "ifcid 6" inconsistent data


>I have found out that the reason for the same page being read a second time
> was that the first time the page was read was due to a "parallel" process.
> When DB2 is reading via a parallel process, the page may be almost
> immediately reused. This keeps a parallel process from stealing all the
> pages
> from a bufferpool.54
>
> The IDUG DB2-L Listserv is only part of your membership in IDUG. DB2-L
> list archives, the FAQ, and delivery preferences are at
> http://www.idug.org/lsidug under the Listserv tab. While at the site, you
> can also access the IDUG Online Learning Center, Tech Library and Code
> Place, see the latest IDUG conference information, and much more. If you
> have not yet signed up for Basic Membership in IDUG, available at no cost,
> click on Member Services at http://www.idug.org/lsms
>
>

The IDUG DB2-L Listserv is only part of your membership in IDUG. DB2-L list archives, the FAQ, and delivery preferences are at http://www.idug.org/lsidug under the Listserv tab. While at the site, you can also access the IDUG Online Learning Center, Tech Library and Code Place, see the latest IDUG conference information, and much more. If you have not yet signed up for Basic Membership in IDUG, available at no cost, click on Member Services at http://www.idug.org/lsms