Re[2]: os block size versus oracle bock size

From: <dgoulet_at_vicr.com>
Date: Tue, 23 Oct 2001 08:11:11 -0700
Message-ID: <F001.003B2311.20011023075022@fatcity.com>

WHOA, No that is not a performance problem. The Oracle block size needs to always be a multiple of the OS block size. Most operating systems today, W2K being no exception, do not simply read the number of OS blocks that you request. They always 'read ahead' in the anticipation that you'll want that data in the very near future. The amount of read ahead that is done is OS specific. Therefore if your Oracle block size is <= the OS block size the operating system will be doing a lot of reading for you that is irrelevant, which can lead to a phantom performance problem namely your wasting OS reads. The idea here is to pick an Oracle block size that is appropriate for your application and a multiple of the OS block size. Also set db_file_multiblock_read_count carefully since this controls the number of blocks that Oracle requests from the OS at one time. If you need one block and have db_file_multiblock_read_count set to 100, then you get 100 blocks, if the OS allows.

Dick Goulet

____________________Reply Separator____________________
Author: nlzanen1_at_EY.NL
Date:       10/23/2001 7:05 AM

I'd say yes. For every Oracle block read the OS has to read two block which causes overhead.

Jack

GKor_at_rdw.nl_at_fatcity.com on 23-10-2001 16:05:21

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hi all

we have an oracle block size of 8k and i believe our W2K server has a default
os block size of 4k.
Is this a problem with the performance ?

thanks

g.g. kor
rdw ict groningen

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