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DBHEAP configuration for buffer pool size

P: n/a
In a DB2 V8.1 performance tuning document from a 3rd party vendor, I
found this statement. Can anyone verify this?

"DB2 requires 100 bytes of memory for every buffer pool and extended
storage page that is allocated to a database for use as a descriptor
in the database heap, so the size of the DBHEAP configuration
parameter should be considered before creating large buffer pools. For
example, a 1 gigabyte buffer pool with a page size of 4 KB will
require approximately 25 megabytes of database heap memory to store
the 262,144 descriptors required by the buffer pool."
Nov 12 '05 #1
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3 Replies


P: n/a
Mark ... this was true in V7.x ... but is "not" true in V8.x since we now use memory pools
in V8.x rather than the old memory model in V7.x.
Some details that may help you ... at a very high level (meaning not all possibilities
have been listed):

For Version 7

In bytes:

(logbufsz * 4K)

+ (catalogcache_sz * 4K)

+ 8K per table space

+ 4K per table

+ 100 bytes per page of Extended Storage

For Version 8

In bytes:

(logbufsz * 4K)

+ 10K per table space

+ 4K per table

+ ( 1K + 4*extents used ) per range clustered table (RCT)

This is documented (and more) at:
http://www-1.ibm.com/support/docview...=utf-8&lang=en
--

Bob
Engagement Specialist - DB2 Information Management Software - IBM Software Group
IBM Toronto Lab
[My comments are solely my own and are not meant to represent an official IBM position -
ask my cat!]

"Mark" <m0****@yahoo.com> wrote in message
news:a5**************************@posting.google.c om...
In a DB2 V8.1 performance tuning document from a 3rd party vendor, I
found this statement. Can anyone verify this?

"DB2 requires 100 bytes of memory for every buffer pool and extended
storage page that is allocated to a database for use as a descriptor
in the database heap, so the size of the DBHEAP configuration
parameter should be considered before creating large buffer pools. For
example, a 1 gigabyte buffer pool with a page size of 4 KB will
require approximately 25 megabytes of database heap memory to store
the 262,144 descriptors required by the buffer pool."

Nov 12 '05 #2

P: n/a
"Bob [IBM]" <Bo******@canada.com> wrote in message
news:2s*************@uni-berlin.de...
Mark ... this was true in V7.x ... but is "not" true in V8.x since we now use memory pools in V8.x rather than the old memory model in V7.x.
Some details that may help you ... at a very high level (meaning not all possibilities have been listed):

For Version 7

In bytes:

(logbufsz * 4K)

+ (catalogcache_sz * 4K)

+ 8K per table space

+ 4K per table

+ 100 bytes per page of Extended Storage

For Version 8

In bytes:

(logbufsz * 4K)

+ 10K per table space

+ 4K per table

+ ( 1K + 4*extents used ) per range clustered table (RCT)

This is documented (and more) at:
http://www-1.ibm.com/support/docview...=utf-8&lang=en --

Bob
Engagement Specialist - DB2 Information Management Software - IBM Software Group IBM Toronto Lab


Thank you for the link. So even for version 7, then the 100 bytes per page
only applies to the use of extended storage for buffer pools?

I don't understand why this stuff is not documented in the manual
("Administration Guide: Performance").
Nov 12 '05 #3

P: n/a
same topic but not same question : what's the advantages of bufferpools in
estore mode ?

Thanks

seb

"Mark A" <no****@nowhere.com> a écrit dans le message de
news:Oj************@news.uswest.net...
"Bob [IBM]" <Bo******@canada.com> wrote in message
news:2s*************@uni-berlin.de...
Mark ... this was true in V7.x ... but is "not" true in V8.x since we now
use memory pools
in V8.x rather than the old memory model in V7.x.
Some details that may help you ... at a very high level (meaning not all possibilities
have been listed):

For Version 7

In bytes:

(logbufsz * 4K)

+ (catalogcache_sz * 4K)

+ 8K per table space

+ 4K per table

+ 100 bytes per page of Extended Storage

For Version 8

In bytes:

(logbufsz * 4K)

+ 10K per table space

+ 4K per table

+ ( 1K + 4*extents used ) per range clustered table (RCT)

This is documented (and more) at:

http://www-1.ibm.com/support/docview...=utf-8&lang=en --

Bob
Engagement Specialist - DB2 Information Management Software - IBM

Software Group
IBM Toronto Lab


Thank you for the link. So even for version 7, then the 100 bytes per page
only applies to the use of extended storage for buffer pools?

I don't understand why this stuff is not documented in the manual
("Administration Guide: Performance").

Nov 12 '05 #4

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