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From "A B (JIRA)" <derby-...@db.apache.org>
Subject [jira] Resolved: (DERBY-781) Materialize union subqueries in select list where possible to avoid creating invariant resultsets many times.
Date Fri, 21 Jul 2006 16:58:14 GMT
     [ http://issues.apache.org/jira/browse/DERBY-781?page=all ]

A B resolved DERBY-781.
-----------------------

    Resolution: Fixed
    Derby Info: [Existing Application Impact, Release Note Needed]  (was: [Existing Application
Impact, Patch Available, Release Note Needed])

Resolving issue as the patch was committed by Satheesh with svn #423989. I'll wait a couple
of days to see if anything comes up and then will close this next week if all is well.

Thanks again to Bryan for the review and to Satheesh for the commit.

> Materialize union subqueries in select list where possible to avoid creating invariant
resultsets many times.
> -------------------------------------------------------------------------------------------------------------
>
>                 Key: DERBY-781
>                 URL: http://issues.apache.org/jira/browse/DERBY-781
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 10.1.1.0, 10.2.0.0
>         Environment: generic
>            Reporter: Satheesh Bandaram
>         Assigned To: A B
>         Attachments: d781_v1.patch, d781_v1.stat, d781_v2.patch, DERBY-781_v1.html
>
>
> Derby's handling of union subqueries in from list can be improved by materializing invariant
resultsets once, rather than creating them many times.
> For example:
> create view V1 as select i, j from T1 union select i,j from T2;
> create view V2 as select a,b from T3 union select a,b from T4;
> insert into T1 values (1,1), (2,2), (3,3), (4,4), (5,5);
> For a query like select * from V1, V2 where V1.j = V2.b and V1.i in (1,2,3,4,5), it is
possible the resultset for V2 is created 5 times. (assuming V2 is choosen as the the inner
table) This can be very costly if the underlying selects can take long time and also may perform
union many times.
> Enhance materialization logic in setOperatorNode.java. It currently returns FALSE always.
> public boolean performMaterialization(JBitSet outerTables)
> 		throws StandardException
> {
> 	// RESOLVE - just say no to materialization right now - should be a cost based decision
> 	return false;
> 	/* Actual materialization, if appropriate, will be placed by our parent PRN.
> 	 * This is because PRN might have a join condition to apply.  (Materialization
> 	 * can only occur before that.
> 	 */
> 	//return true;
> } 

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