Re: Performance of MERGE INTO statement

  • From: "Finn Jorgensen" <finn.oracledba@xxxxxxxxx>
  • To: "Hostetter, Jay M" <JHostetter@xxxxxxxxxxxxxxxxxxxx>
  • Date: Wed, 14 May 2008 15:31:02 -0400

Jay,

I'm not a warehouse expert, but I do know that frequent writes to
tables with bitmap indexes on it is not a good idea (once a day is
frequent in DW's). It causes the bitmap indexes to grow uncontrolably
and become slow. From my understanding it is typical to rebuilt the
bitmap indexes after a data load is complete, but when you load data
that frequently that may not be an option.

Somebody with more DW experience may chime in here.

Thanks,
Finn

On 5/14/08, Hostetter, Jay M <JHostetter@xxxxxxxxxxxxxxxxxxxx> wrote:
>  I'm processing millions of call records per
> day.  The lowest level of detail in the fact table for the call date is
> "day".  So I could update the fact table once a day from a staging
> table.  The tricky part is that some calls span more than one day, so I
> can have call records trickle in several days later.  This is why I went
> with the merge statement, because I may need to update fact records.  Of
> course, now as I think about it, a few duplicate fact records don't seem
> like they would be a problem (although that goes against my instincts
> from an OLTP point of view).
>
> Thanks,
> Jay
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