Re: db_file_multiblock_read_count

From: Wolfgang Breitling <breitliw000_at_centrexcc.com>
Date: 1997/09/10
Message-ID: <5v67jt$gca$1@tor-nn1.netcom.ca>#1/1

In article <34118AE4.4F4C7477_at_mail.telepac.pt>, Nuno Martins <nunomartins_at_mail.telepac.pt> wrote:
>
>Hello,
>if i have a db_file_multiblock_read_count = 32 then it thas not make
>sense having a index in tables with less than 64k . Is this true ?
>
>What´s are your opinion ?

The cost-based optimizer will not use an index on tables with 5 blocks or less ( rather than a constant, this may actually be related to the init parameter small_table_threshold). Beyond that, it will consider indexes even for tables that can be read with one multi-block I/O. And I have examples where that IS faster. Of course, the rule based optimizer will consider any index regardless of table size. And so does the CBO in the absence of statistics.

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Wolfgang Breitling
certified Oracle DBA

email: breitliw_at_centrexcc.com

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Received on Wed Sep 10 1997 - 00:00:00 CDT