RE: locking issues

Bitmap indexes expand under two conditions:

1. you add a new row (each row in the bitmap index grows by one value)
2. you add a new possible value (an additional row is added to the index, the length is equal to the number of rows in the table)

so when you update a value, you have to update ALL the rows in the bitmap and the index is locked.

each row in a bitmap, unlike a "normal" index, is not the value of that column in that particular row, but is instead a "chain" of on/off bits for that value. Each bit positionally represents a row in the table.

>From: "Koivu, Lisa" <lkoivu_at_qode.com>
>Reply-To: ORACLE-L_at_fatcity.com
>To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
>Subject: RE: locking issues
>Date: Tue, 08 Aug 2000 13:44:17 -0800
>
>Oh. I thought it was just because the bitmap indexes expand like crazy
>when
>the indexed column is updated - not because there was locking issues.
>
>Thanks Rachel.
>
>-----Original Message-----
>Sent: Tuesday, August 08, 2000 4:35 PM
>To: Multiple recipients of list ORACLE-L
>
>
>yes. which is why Oracle recommends you not use bitmap indexes on tables
>that have that column frequently updated
>
>
> >From: "Koivu, Lisa" <lkoivu_at_qode.com>
> >Reply-To: ORACLE-L_at_fatcity.com
> >To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> >Subject: RE: locking issues
> >Date: Tue, 08 Aug 2000 10:06:07 -0800
> >
> >WHAT?
> >
> >"whenever any row that the bitmap points to is locked"
> >
> >Do you mean that an entire table ends up being locked if I am updating
>one
> >row and there is a bitmap index on it?
> >
> >-----Original Message-----
> >Sent: Tuesday, August 08, 2000 1:37 PM
> >To: Multiple recipients of list ORACLE-L
> >
> >
> >Yes. Bitmap indexes are locked whenever any row that the bitmap points to
> >is
> >locked -- which could mean 1000s of rows are locked whenever 1 row is
> >updated!
> >
> >And, yes. This was part of the original problem. When we dropped the
>bitmap
> >index, we still got deadlocking -- until I rewrote the code to clean up
>the
> >logic.
> >
> >Kevin
> >
> > > -----Original Message-----
> > > From: Jamadagni, Rajendra [mailto:rajendra.jamadagni_at_espn.com]
> > > Sent: Tuesday, August 08, 2000 12:33 PM
> > > To: Multiple recipients of list ORACLE-L
> > > Subject: RE: locking issues
> > >
> > >
> > > Isn't it true that Bitmap indexes lock more than necessary
> > > rows ? I mean if
> > > you are updating only one row, when bitmap index gets
> > > updated, it locks all
> > > the rows that are in the same (index) data block. Could this
> > > be one of the
> > > problem?
> > >
> > > I may be wrong, but I know someone will correct me on this ...
> > >
> > > Cheers
> > > Raj
> > > ______________________________________________________
> > > Rajendra Jamadagni MIS, ESPN Inc.
> > > Rajendra dot Jamadagni at ESPN dot com
> > > QOTD: Any clod can have facts, but having an opinion is an art !
> > > Any opinion expressed here is personal and doesn't reflect
> > > that of ESPN Inc.
> > >
> > > --
> > > Author: Jamadagni, Rajendra
> > > INET: rajendra.jamadagni_at_espn.com
> > >
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> >Author: Toepke, Kevin M
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>--
>Author: Rachel Carmichael
> INET: carmichr_at_hotmail.com
>
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