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From "Kathey Marsden (JIRA)" <derby-...@db.apache.org>
Subject [jira] Updated: (DERBY-781) Materialize union subqueries in select list where possible to avoid creating invariant resultsets many times.
Date Wed, 19 Jul 2006 16:15:14 GMT
     [ http://issues.apache.org/jira/browse/DERBY-781?page=all ]

Kathey Marsden updated DERBY-781:
---------------------------------

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

There may be  existing application impact as applications may see increased compilation times
but should see improved execution time performance.  Applications may want to adjust to use
PreparedStatements instead of Statements  (always a good practice with Derby).

> 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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