RE: db_file_multiblock_read_count 10g default values

From: Allen, Brandon <Brandon.Allen_at_OneNeck.com>
Date: Thu, 5 Nov 2009 15:18:23 -0700
Message-ID: <64BAF54438380142A0BF94A23224A31E112E739FFA_at_ONEWS06.oneneck.corp>

I just did some more testing and you were right about the it being based on the processes parameter too as you can see in the table below with __db_cache_size held consant at 200M (and sga_target=400M), so my earlier formula only holds true when processes <= 300, but once you get above that, then db_file_multiblock_read_count is gradually scaled back, so I don't know the exact formula, but I think we can definitely conclude that db_file_multiblock_read_count is directly related to db_cache_size and inversely related to processes.

Regards,
Brandon

processes       __db_cache_size dbfmbrc dbfmbrc*db_block_size(8k)       dbfmbrc*db_block_size/db_cache_size


---------       --------------- ------- -------------------------       -----------------------------------

50              201326592               70              573440                          0.0028
100             201326592               70              573440                          0.0028
200             201326592               70              573440                          0.0028
300             201326592               70              573440                          0.0028
400             201326592               53              434176                          0.0022
500             201326592               42              344064                          0.0017
600             201326592               35              286720                          0.0014
700             201326592               30              245760                          0.0012
800             201326592               26              212992                          0.0011
1000            201326592               21              172032                          0.0009
2000            201326592               10              81920                                   0.0004

-----Original Message-----

From: Greg Rahn [mailto:greg_at_structureddata.org]

The choice for db_file_multiblock_read_count when not set is dependent on some other parameters (IIRC buffer cache size, sessions/processes, likely some others)

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http://www.freelists.org/webpage/oracle-l Received on Thu Nov 05 2009 - 16:18:23 CST