Re: Bitmap vs btree - how to tell? how to test?

From: Rachel Carmichael <wisernet100_at_yahoo.com>
Date: Sat, 25 May 2002 13:38:18 -0800
Message-ID: <F001.0046BAA3.20020525133818@fatcity.com>

low cardinality -- good candidate for bitmap. little or no updates to the column being indexed -- good candidate for bitmap

"low" cardinality is relative -- 10,000 distinct values in a 300m row table is low, 100 distinct values in a 10K row table might be high

but the main criteria I have found is whether or not the column is updated because when you update the values in a bitmap index, it's not just the one row in the index that is updated but the entire segment of the bitmap. And THAT can lock the index on you.

Rachel

• Jack Silvey <jack_silvey_at_yahoo.com> wrote:
  > Listers,
  >
  > We are creating indexes on a 300m row fact table
  > today. I am researching bitmap versus btree (again) to
  > see where the latest info points.
  >
  > Anyone care to comment on the way to determine whether
  > an index should be a btree or a bitmap? Anyone even
  > know a good way to test this?
  >
  > thx,
  >
  > /jack
  >
  >
  > __________________________________________________
  > Do You Yahoo!?
  > LAUNCH - Your Yahoo! Music Experience
  > http://launch.yahoo.com
  > --
  > Please see the official ORACLE-L FAQ: http://www.orafaq.com
  > --
  > Author: Jack Silvey
  > INET: jack_silvey_at_yahoo.com
  >
  > Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
  > San Diego, California -- Public Internet access / Mailing
  > Lists
  > --------------------------------------------------------------------
  > To REMOVE yourself from this mailing list, send an E-Mail message
  > to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
  > the message BODY, include a line containing: UNSUB ORACLE-L
  > (or the name of mailing list you want to be removed from). You may
  > also send the HELP command for other information (like subscribing).
  

  ---

Do You Yahoo!?
Yahoo! - Official partner of 2002 FIFA World Cup http://fifaworldcup.yahoo.com

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Rachel Carmichael
  INET: wisernet100_at_yahoo.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).

Received on Sat May 25 2002 - 16:38:18 CDT