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From "Daniel John Debrunner (JIRA)" <derby-...@db.apache.org>
Subject [jira] Closed: (DERBY-742) Use a single result BooleanDataValue for a boolean expression in class generation
Date Tue, 11 Jul 2006 23:39:31 GMT
     [ http://issues.apache.org/jira/browse/DERBY-742?page=all ]
Daniel John Debrunner closed DERBY-742:

> Use a single result BooleanDataValue for a boolean expression in class generation
> ---------------------------------------------------------------------------------
>          Key: DERBY-742
>          URL: http://issues.apache.org/jira/browse/DERBY-742
>      Project: Derby
>         Type: Sub-task

>   Components: SQL
>     Reporter: Daniel John Debrunner
>     Assignee: Daniel John Debrunner
>     Priority: Minor
>      Fix For:

> BinaryLogicalOperatorNode.generateExpression() creates a BooleanDataValue for the result
of the expression, this is to avoid object generation during runtime.
> The code is logically like (ignoring the short circuit logic) for the SQL <left>
AND <right>
> BooleanDataValue   e34; // instance field for the result
>  e34 = <left>.and( <right>,  e34);
> The and method on BooleanDataValue will create a new BooleanDataValue if the passed in
e34 is null, otherwise re-use it.
> On the first execution e34 will be null, and thus the 'and' method will create an object
and it will get stored in e34.
> [ Ignore for the moment the inefficiency of setting e34 everytime to the same value on
every subsequent execution. ]
> [ This approach is standard practice in the generated code and elsewhere and ensures
that  object allocation within a Derby ]
> [ statement execution is a fixed cost, and not linear with the number of rows scanned.
> This issue is about what happens when multiple boolean expressions get combined, as in
the query in DERBY-732. For each AND/OR
> a new BooleanDataValue field is created to hold the result of the intrermediate step,
e.g. for the SQL ( <A> AND <B> ) AND <C>
> BooleanDataValue   e34; // instance field for the result of A and B
> BooleanDataValue   e35; // instance field for the final result
>  e34 = <A>.and( <B>,  e34);
>  e35 = <e34>.and(<C>, e35);
> But since this is a single expression, of the same type up and down the tree, why not
 have a single BooleanDataValue for the result
> BooleanDataValue   e36; // instance field for the final result
>  e36 = <A>.and( <B>,  e36);
>  e36 = <e36>.and(<C>, e36);
> or
> e36 = new BooleanDataValue(); // through data value factory
> <A>.and( <B>,  e36);
> <e36>.and(<C>, e36);
> The query for DERBY-732 has over 500 BooleanDataValue   fields, which I think are all
intermediate result holders.
> Would need to document that the and and or methods return the result passed in if it
is not null, which I think is the case for
> all DataValueDescriptor methods that take a result parameter.
> [ [ 

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