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Re: undocumented parameters

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Ricardo;


These are paired hidden parameters that tune the sizes of the data
dictionary cache (DD_HASHMAX, DD_HASHSIZE); the data distribution cache,
(DS_HASHSIZE, DS_POOLSIZE); and the stored procedure cache (PC_HASHSIZE,
PC_POOLSIZE).

These parameters are documented in the Performance Guide.

DD_HASHMAX, DS_HASHSIZE, and PC_HASHSIZE need to be prime numbers, and set
the number of lists for the cache. The companion parameters set the number
of items in each list.

The data dictionary cache, for example, defaults to DD_HASHMAX of 31 and
DD_HASHSIZE of 10. That means that 310 data dictionary items are cached.
If you have more than 310 tables open and active at one time, then some of
these are going to be flushed out and the data dictionary re-read from disk
next time the table is accessed.

Same concept for data distributions and stored procedures.
Both these caches default to 31 lists, 127 items in each list.

You can help performance by sizing each of these to cache the number of
concurrent active and open objects your instance and application uses - not
necessarily just to the total number of tables/distributions/procedures.
To change them from the defaults, add them with the desired values to the
onconfig file and bounce the engine.

You can monitor these caches using onstat commands:
Data Dictionary
onstat -g dic

Data Distribution
onstat -g dsc

Stored Procedure
onstat -g prc

HTH...
Mike
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Mike Lowe
Certified Consulting Education Specialist
Data Management Solutions
IBM Software Group
Tel: 303-773-5216 Tie Line: 565-5216
e-Fax: 413-674-2415
mlowe0@us.ibm.com
WWW: ibm.com/software/data



Hi all ,



Does anybody know the meaning about the parameters below and how does it
affect performance ?

DD_HASHSIZE
DS_HASHSIZE
DS_POOLSIZE
PC_POOLSIZE
PC_HASHSIZE

Thanks


Ricardo

Messages In This Thread

• undocumented parameters
  Ricardo Manzo -- Wednesday, 12 March 2003, at 3:05 p.m.
  • Re: undocumented parameters
    Michael Lowe -- Wednesday, 12 March 2003, at 3:49 p.m.

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