| setting db_file_multiblock_read_count [message #221913] |
Thu, 01 March 2007 00:56  |
Brayan
Messages: 315
Registered: June 2002
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Senior Member |
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Hi,
I have an Data Warehouse environment with Oracle 9.2.
I have set the db_file_multiblock_read_count = 8
The recommended count will be from the following
max I/O chunk size
db_file_multiblock_read_count = -------------------
db_block_size
How to get the "max I/O chunk size" ??
Brian.
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| Re: setting db_file_multiblock_read_count [message #221917 is a reply to message #221913] |
Thu, 01 March 2007 01:20  |
michael_bialik
Messages: 621
Registered: July 2006
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Senior Member |
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Hi.
AFAIK (max I/O chunk size) is OS-dependant and is 64K for Unix systems.
However IMHO Oracle does NOT consider it and just uses db_file_multiblock_read_count number during full tabl;e scans (the greater that number is - the cheaper FTS cost), so
assigning large value for it may cause your system to abandon index accesses.
HTH.
Michael
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| Re: setting db_file_multiblock_read_count [message #222003 is a reply to message #221913] |
Thu, 01 March 2007 07:48 |
smartin
Messages: 1803
Registered: March 2005
Location: Jacksonville, Florida
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Senior Member |
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Tom Kyte in his Effective book (possibly also his new one, I don't know) has a nice walkthrough of this parameter and how to determine how to set it. Especially if you are running 9iR2 in production, it is a good book to have, even well beyond this one issue.
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