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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DERBY-5989) Stop producing byte code for non-existent qualifiers
Date Mon, 12 Nov 2012 08:22:12 GMT
Knut Anders Hatlen created DERBY-5989:
-----------------------------------------

             Summary: Stop producing byte code for non-existent qualifiers
                 Key: DERBY-5989
                 URL: https://issues.apache.org/jira/browse/DERBY-5989
             Project: Derby
          Issue Type: Improvement
          Components: SQL
    Affects Versions: 10.10.0.0
            Reporter: Knut Anders Hatlen
            Assignee: Knut Anders Hatlen
            Priority: Minor


For all result set nodes that have predicate lists, Derby's compiler lays out byte code for
fields to hold qualifiers, and also code to reinitialize the values in those fields on every
execution. It does this even if there are no qualifiers. See PredicateList.generateQualifiers().
That method does actually check whether there are qualifiers, and it skips some of the code
generation if there are none. It should be changed so that it skips all the code generation
if there are no qualifiers.

For an example, see the decompiled generated class for a natural join attached to DERBY-5947:
https://issues.apache.org/jira/secure/attachment/12549514/natural-join-after-3a.txt

That class contains three Qualifier[][] fields:

    private Qualifier[][] e1;
    private Qualifier[][] e3;
    private Qualifier[][] e4;

Only one of them (e4) is ever set to a non-null value. Still, the reinit() method, which is
called on every execution, has code for each of the fields:

    protected void reinit() throws StandardException {
	BaseActivation.reinitializeQualifiers(e1);
	BaseActivation.reinitializeQualifiers(e3);
	BaseActivation.reinitializeQualifiers(e4);
    }

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