[jira] Reopened: (DERBY-742) Use a single result BooleanDataValue for a boolean expression in class generation

["Kathey Marsden (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/DERBY-742?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Kathey Marsden reopened DERBY-742:
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reopen to backport to 10.1


> Use a single result BooleanDataValue for a boolean expression in class generation
> ---------------------------------------------------------------------------------
>
>                 Key: DERBY-742
>                 URL: https://issues.apache.org/jira/browse/DERBY-742
>             Project: Derby
>          Issue Type: Sub-task
>          Components: SQL
>            Reporter: Daniel John Debrunner
>            Assignee: Daniel John Debrunner
>            Priority: Minor
>             Fix For: 10.2.1.6
>
>
> 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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