Re: UNION ALL PUSHED PREDICATE Question

From: Andrew Kerber <andrew.kerber_at_gmail.com>
Date: Wed, 27 Aug 2008 14:22:32 -0500
Message-ID: <ad3aa4c90808271222k39c133e7kc109f1e63ece8cb3@mail.gmail.com>


I am pretty sure this is a known Oracle bug. I think read something about it some time ago.

On Wed, Aug 27, 2008 at 1:55 PM, Michael Schmitt <mschmitt_at_uchicago.edu>wrote:

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> Hi All,
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> I had a question about "UNION ALL PUSHED PREDICATE", and I was hoping
> someone could point me in the right direction (this is for a 10.2.0.3database). We have a query that does not push the predicate into a view if
> we have a local bitmap index on a partitioned table sitting behind the view.
> If we drop the local bitmap index on one of the columns, then we see the
> UNION ALL PUSHED PREDICATE, the query uses partition pruning, and the query
> returns in a fraction of the time. I am trying to find out how the bitmap
> index is affecting the pushed predicate and the optimizer plan taken. The
> partitioned table sits behind a view and does a UNION ALL onto itself a
> couple of times.
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> An example of the view is as follows.
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> Create view v_TEST () as
>
> Select x,y,z from t_TEST where col_1 is not null bitmap is for this
> column
>
> UNION ALL
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> Select u,t,v from t_TEST where col_2 in (.)
>
> UNION ALL
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> Select u,m,p from t_TEST where col_3 in (.)
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>
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> And the query looks like this
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> Select v_test.col_X from v_test, t_2
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> Where t_2.col_4 = v_test.col4
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> And t_2.col_1 = '200805'
>
>
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> The column with the local bitmap index is col_1 from the view above. I
> have gathered 10053 traces, but I am not familiar with sorting through that
> data and have not found what I have been looking for. When the bitmap index
> exists on col_1, the optimizer scans all of the partitions of t_TEST and
> chooses a plan that costs 80K. When the index does not exist (and we see
> partition pruning of t_TEST), then the optimizer chooses a plan that costs
> 6k and completes in a fraction of the time.
>
>
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> What I am trying to figure out is why the optimizer does not push the
> predicate into the view (and use partition pruning) when the bitmap index
> exists on t_TEST.col. Any pointers would be appreciated
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> Thanks in advance, and sorry if I did not provide all the needed
> information.
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-- 
Andrew W. Kerber

'If at first you dont succeed, dont take up skydiving.'

--
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Received on Wed Aug 27 2008 - 14:22:32 CDT

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