Re: db_file_multiblock_read_count

Wolfgang Breitling wrote:

> 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.
>
> ____________________________________________
> Wolfgang Breitling
> certified Oracle DBA
>
> email: breitliw_at_centrexcc.com
>
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> ____________________________________________

  And there is examples where is not faster ? how did you measured that ?
  I tried tkprof and it shows that with index still makes less physical reads , the elapse time in both cases is 0 . Received on Thu Sep 11 1997 - 00:00:00 CDT