Re: Disadvantages of Bitmap Indexes?

joseharvey_at_my-deja.com wrote:
>
> Hi gurus,
> I have a table containing about a million records. One column refers to
> an object type used as a foreign key to another table; there are about
> 150 different possible values. I think a bitmap index would be a good
> choice here; on our test environment it emproves performance
> dramatically. However, on my documentation there is a sentence about
> locking that makes me hesitate:
>
> "Bitmap indexes benefit data warehousing applications but they are not
> appropriate for OLTP applications with a heavy load of concurrent
> INSERTs, UPDATEs, and DELETEs."
>
> What is the meaning of "heavy load"? On my application, there will be
> about 1200 rows per week inserted on this table, performed by up to 150
> users. Will the bitmap index decrease performance considerably?
>
> Thanks for your answers
>
> Jose Harvey
>
> --
> -=[ Sancho ]=-
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.

Typically every row with a given value will be locked...

The worst case would be a column with two distinct values (say 1 and 2). Updating 1 to 2 would leave the whole table locked until commit...

HTH

-- 
===========================================
Connor McDonald
http://www.oracledba.co.uk
(faster/mirrored at http://www.oradba.freeserve.co.uk)

Its not the voices in my head that bother me... 
  its the voices in yours.