RE: Btmap Index

From: Trassens, Christian <CTrassens_at_uni2.es>
Date: Tue, 9 Jan 2001 15:12:47 +0100
Message-Id: <10736.126121@fatcity.com>

Perhaps an histogram could help to recognize it. Because CBO assumes an = even
distribution.

B_TREE_BITMAP_PLANS=3DTRUE could be the parameter you've been looking = for.
However in 8i is hidden and in some situation uses a btree as a bitmap, converting it.

> -----Mensaje original-----
> De: Kevin Kostyszyn [SMTP:kevin_at_dulcian.com]
> Enviado el: martes 9 de enero de 2001 0:50
> Para: Multiple recipients of list ORACLE-L
> Asunto: Re: Btmap Index

>=20
> I ran into a similar problem a while back. If the database is set to =
use
> the CBO, it might not use the index. Someone on this list gave a =
great
> reason why, perhaps the table is just very small and the CBO just =
decided
> to do a full table scan instead. You could use a hint and tell it to =
use
> rule based on that query and it will use the index on the where =
clause.
> That's what I did. The question is, how big is the table and how =
much
> data does it have in it? If it is not a lot, there really is nothing =
to
> be concerned about. Oh yeah, and almost 100% positive that there is =
no
> setting in the init file for the index. =20
> Sincerely,
> Kevin

>=20


> 	----- Original Message -----=20

> 	From: Krishna Prasad <mailto:krishna_at_nehanet.com>=20

> 	To: Multiple recipients of list ORACLE-L

> <mailto:ORACLE-L_at_fatcity.com>=20

> 	Sent: Monday, January 08, 2001 5:45 PM

> 	Subject: Btmap Index

>=20


> 	Hi,

> 	=20

> 	Is there any init.ora parameter that needs to be turned to activate

> bitmap indexes?

> 	I have a bitmap index on one column C1, but when i examine the

> explain pan of the=20

> 	query: " select C1, b, c from table TT where C1 in ('dd','ff')" , it

> looks like it is not using

> 	the index but doing a full table scan...

> 	=20

> 	thanks

> 	-krishna

>=20


> 		-----Original Message-----

> 		From: root_at_fatcity.com [mailto:root_at_fatcity.com]On Behalf Of

> Jacques Kilchoer

> 		Sent: Monday, January 08, 2001 2:01 PM

> 		To: Multiple recipients of list ORACLE-L

> 		Subject: RE: Date comparison question

> 	=09

> 	=09

>=20


> 		> -----Original Message-----=20

> 		> From: Lisa Yates [ <mailto:cosnit_at_creighton.edu>]=20

> 		> Sent: lundi, 8. janvier 2001 11:27=20

> 		>=20

> 		> Why doesn't this query ever return...=20

> 		>=20

> 		> where run_date =3D to_date('01-03-2001 16:34:59','mm-dd-yyyy

>=20


> 		> hh24:mi:ss')=20

> 		>=20

> 		> but this query does....=20

> 		>=20

> 		> where to_char(run_date) =3D to_char(to_date('01-03-2001=20

> 		> 16:34:59','mm-dd-yyyy hh24:mi:ss'))=20

> 		>=20

> 		> and so does this query....=20

> 		>=20

> 		> where to_char(run_date,'mm-dd-yyyy hh24:mi:ss') =3D

> '01-03-2001=20

> 		> 16:34:59'=20

>=20


> 		Well, I guess my suggestion that run_date may contain a

> "BCE" (before common era) date was not the answer to your problem. =
Maybe I
> misunderstood the issue. When you say "why doesn't the query ever =
return",
> do you mean it returns zero rows, or do you mean that the query is =
taking
> an abnormally long time? If it's taking an abnormally long time, an
> explain plan on the two queries may reveal the cause.

>=20


> 		Jacques R. Kilcho=EBr=20

> 		(949) 754-8816=20

> 		Quest Software, Inc.=20

>=20


> 		8001 Irvine Center Drive=20

Received on Tue Jan 09 2001 - 08:12:47 CST