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  #1 (permalink)  
Old 09-08-06, 05:41
Meena.s Meena.s is offline
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DB parameter....
Hi.......all

i want to know about the db parameter....default prefetch size.......

In db2 get db cfg command,it is showing........

Default prefetch size (pages) (DFT_PREFETCH_SZ) = AUTOMATIC

(DFT_EXTENT_SZ) = 32.

The prefetch size may be half the extent size or multiples of the extent size...right?

then what does AUTOMATIC refers to.........

what size DB2 will take......

THANKS.
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Old 09-08-06, 06:03
sathyaram_s sathyaram_s is offline
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Meena
If the parameter is set to AUTOMATIC, DB2 calculates the value based on the following equation
prefetch size = (# containers) * (# physical spindles) * extent size

The prefetch size is calculated at database startup time and when a tablespace is created or altered

HTH

Sathyaram
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Old 09-08-06, 06:04
sathyaram_s sathyaram_s is offline
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BTW, where did you read that the prefetch size may be half the extent size ?

Sathyaram
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Old 09-11-06, 08:04
Meena.s Meena.s is offline
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Hi.....

Actually i read this from DB2 information center.From the following site....

http://publib.boulder.ibm.com/infoce...dex.jsp.Thanks for ur information.

Thanks
Meena
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Old 09-12-06, 13:27
cchattoraj cchattoraj is offline
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Question
Quote:
Originally Posted by sathyaram_s
Meena
If the parameter is set to AUTOMATIC, DB2 calculates the value based on the following equation
prefetch size = (# containers) * (# physical spindles) * extent size

The prefetch size is calculated at database startup time and when a tablespace is created or altered

HTH

Sathyaram
How does db2 determine the number of physical Spindles?
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Old 09-13-06, 05:36
sathyaram_s sathyaram_s is offline
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Search for DB2_PARALLEL_IO in the documentation

Sathyaram
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Old 09-13-06, 06:01
Meena.s Meena.s is offline
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The number of physical spindles defaults to 1 and can be specified through the DB2 registry variable DB2_PARALLEL_IO.

Thanks
Meena
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Old 09-13-06, 06:55
sathyaram_s sathyaram_s is offline
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The number is 1 if you have not enabled parallel io

If you have, IIRC, the number is 6 ..

For most 'modern' systems, you will have to set parallel io for exploiting the IO capability

Sathyaram
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Old 09-13-06, 14:06
cchattoraj cchattoraj is offline
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I understood that setting DB2_PARALLEL_IO=6 enables parallel io for tbsp whose tablespace-id is 6. If it is set to * enables parallel io for all tablespaces.

When I read your response I thought that maybe IBM changed what it meant in subsequent versions so I checked IBM's website and the definition of this registry variable does not appear to have changed.

So the question remains - how is db2 informed of the number of physical spindles in the RAID group.
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Old 09-13-06, 14:43
sathyaram_s sathyaram_s is offline
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Old 09-13-06, 15:10
cchattoraj cchattoraj is offline
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It does, thanks.
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