[ http://issues.apache.org/jira/browse/DERBY-781?page=all ]

A B updated DERBY-781:
----------------------

    Attachment: d781_v2.patch

Attaching an updated patch, d781_v2.patch, that is synced with the latest codeline and that also has a small fix to the lang/subquery test (there was a typo in the first patch).  Other than the minor test fix, this patch is identical to the _v1 patch.

Still awaiting review, if anyone has the time...

> 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
>         Type: Improvement

>   Components: SQL
>     Versions: 10.1.1.0, 10.2.0.0
>  Environment: generic
>     Reporter: Satheesh Bandaram
>     Assignee: A B
>  Attachments: DERBY-781_v1.html, d781_v1.patch, d781_v1.stat, d781_v2.patch
>
> 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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