Re: multiblock read count

In article <8pqa2s$pjm$1_at_xs4.xs4all.nl>,   rjn_at_pobox.com (Fidelio) wrote:
> Hi,
>
> I have db_file_multiblock_read_count set to 16 and my block size
> is 4K. I remember reading somewhere that for optimal performance
> db_file_multiblock_read_count * db_block_size should be 64 KB.
>
> Is this still true for Oracle 8 ? If you have loads of 500 MB
> tables with 300 MB indexes, does the performance still get a
> increase by specifying a larger multiblock read count ?
>
> R
> --
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Multi-block read count only comes into effect for full table scans (and maybe fast full index scans). In the past it has been recommended to set this parameter equal to the OS maximum number of bytes that can be read in one IO request which is usually 64K or 128K on most UNIX systems. However, the setting effects the CBO optimizer and larger settings influence it to choose full table scans over indexes so you may want to set this parameter below it OS dependent maximum setting. The number of blocks is Oracle block size dependend but based on the Performance and Tuning Class Student notes it would appear that the cutoff  is 64K ( 8 8K blocks ). And this is where I imagine the 64K number comes from.

• Mark D. Powell -- The only advice that counts is the advice that you follow so follow your own advice --

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Before you buy. Received on Thu Sep 14 2000 - 08:28:41 CDT