Re: Binary Index Goes Bananas

Yes..sorry, I meant bitmap.

Thomas Kyte wrote:

> A copy of this was sent to Doug Cowles <dcowles_at_bigfoot.com>
> (if that email address didn't require changing)
> On Sun, 04 Jul 1999 14:35:01 -0400, you wrote:
>
> >I found a column with very low cardinality - 2 possible values in
> >a table of 261,000 or so records. I created a binary index.
> >Low and behold, a developer asked me why there would be a problem
> >extending index space if they weren't doing any updates..(questionable
> >wether they
>
> what is a binary index?
>
> do you mean BITMAP or B*Tree.
>

Bitmap

> If it is a B*Tree -- don't index something with 2 discrete values.
>
> >were or not....but ).
> >I never found out wether they were really doing updates or not, but
> >after
> >adding 500MB of space to the index space, they got the same error.
>
> the same error as what?
>

Essesntially they were getting an "unable to extend..." error on the tablespace with the bitmap index citing the name of the index.

> >Even if they were doing updates or inserts, doesn't this sound a little
> >bit
> >like a huge amount of space for a binary index to be taking?
> >Do binary indexes traditionally belong in non-updated tables?
> >
>
> if you mean bitmap, then the answer is maybe. the maintainence of a bitmap
> index is higher then that of other index types but you have to trade that off
> for the increase in performance of queries.
> >- Dc.
>

Yes it was a bitmap, and it seemed to grab 500MB of space which seemed enormously high.. Perhaps this is something that would be reclaimed later after index had been recompressed.

> --
> See http://govt.us.oracle.com/~tkyte/ for my columns 'Digging-in to Oracle8i'...
> Current article is "Part I of V, Autonomous Transactions" updated June 21'st
>
> Thomas Kyte tkyte_at_us.oracle.com
> Oracle Service Industries Reston, VA USA
>
> Opinions are mine and do not necessarily reflect those of Oracle Corporation
Received on Mon Jul 05 1999 - 19:22:18 CDT