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Posted to derby-dev@db.apache.org by "Satheesh Bandaram (JIRA)" <de...@db.apache.org> on 2006/01/04 21:19:01 UTC
[jira] Updated: (DERBY-781) Materialize union subqueries in select list where possible to avoid creating invariant resultsets many times.
[ http://issues.apache.org/jira/browse/DERBY-781?page=all ]
Satheesh Bandaram updated DERBY-781:
------------------------------------
Comment: was deleted
> 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
>
> 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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