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