ny experience with the init parameter _pga_max_size ?

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07-09-2004, 06:29 PM
mike9

Any experience with the init parameter _pga_max_size ?

Hi,

I'm working on DWH Project using Oracle 9.2.0.5 Our production servers has 20cpus and around 40Gb of ram. The pga_aggregate_target is set to 16GB and workarea_size_policy is set to AUTO.

The big problem we have is that from these 16GB of PGA only 5GB are used (based on V$PGASTAT). The reason for that is that Oracle never allocates more then 100MB of PGA to a serial or a parallel process.

So to improve the performance of these queries which need more then 100MB of PGA I was thinking about to use the parameter "_pga_max_size" and to set it to 256MB.

Has anybody so experience with this parameter?

Thanks for any feedback

http://www.dbasupport.com/forums/sho...threadid=41361
07-12-2004, 03:31 PM
tamilselvan

For A DW system, I would not opt for PGA_AGGREGATE_TARGET. Primarily this parameter is designed for OLTP system.

Use "_size" parameters optimally.

Tamil
07-13-2004, 07:08 AM
reydp

maybe tamil is referring to sort_area_size
07-13-2004, 09:05 AM
tamilselvan

Code:

I am talking about the following parameters: bitmap_merge_area_size integer 1048576 create_bitmap_area_size integer 8388608 db_16k_cache_size big integer 0 db_2k_cache_size big integer 0 db_32k_cache_size big integer 419430400 db_4k_cache_size big integer 0 db_8k_cache_size big integer 0 db_block_size integer 8192 db_cache_size big integer 3774873600 db_keep_cache_size big integer 419430400 db_recycle_cache_size big integer 0 global_context_pool_size string hash_area_size integer 33554432 java_max_sessionspace_size integer 0 java_pool_size big integer 33554432 large_pool_size big integer 33554432 max_dump_file_size string 10240000 object_cache_max_size_percent integer 20 object_cache_optimal_size integer 10240000 olap_page_pool_size integer 33554432 oracle_trace_collection_size integer 5242880 parallel_execution_message_size integer 2152 sga_max_size big integer 5142974552 shared_pool_reserved_size big integer 30000000 shared_pool_size big integer 301989888 sort_area_retained_size integer 2097152 sort_area_size integer 32554432

Tamil
07-14-2004, 01:30 AM
reydp

thanks a:confused: tamil,
but may i know what is the most influencing parameter among the *_size that greatly influence the use of PGA especially in a DWH?
07-14-2004, 06:52 AM
mike9

reydp,

I would say that this depends on how your DWH is set up and how good your Data Marts have been designed. The 2 Parameters which will probably influence the most the total size of the PGA are the parameters sort_area_size and hash_area_size.

Tamil,

Thanks for your input. From what I found out so far I totaly agree with you that the "new" PGA management is not suitable for large DWH applications where you have a lot memory but only a few concurent users. That should be much better documented in the Oracle Doc.

I will try to convince my DBA to set the workarea policy to manual and set the PGA parameters back to the value they had when we were using 8i.
07-15-2004, 05:05 AM
reydp

Quote:

Originally posted by mike9
reydp,

I would say that this depends on how your DWH is set up and how good your Data Marts have been designed. The 2 Parameters which will probably influence the most the total size of the PGA are the parameters sort_area_size and hash_area_size.

mike9,
I just thought for a while if there are other init parameters that greatly influence the PGA more than the sort_area_size.
07-15-2004, 09:19 AM
tamilselvan

Apart from the "_size" parameters, the most influence parameter is PROCESSES. Depending upon the value of PROCESSES parameter, Oracle determines the max size for each process within the PGA memory. That is why I said, for DW system , it is not advisable to use PGA.

You may set processes to 200 in the init.ora, but in real life only 10 or 12 users use the system.

Tamil