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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DERBY-5989) Stop producing byte code for non-existent qualifiers
Date Mon, 12 Nov 2012 13:07:12 GMT

     [ https://issues.apache.org/jira/browse/DERBY-5989?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Knut Anders Hatlen updated DERBY-5989:

    Attachment: after.txt

Attaching a patch, d5989-1a.diff, that makes PredicateList.generateQualifier() return immediately
and just lay out code for pushing null onto the stack if there are no qualifiers in the predicate
list. Before, it would create a field that was always null, add code to reset the field on
each execution, and push the field value (always null) onto the stack. The end result should
be the same, just with less code.

Most of the changes in the patch are whitespace changes because some conditionals could be
removed, and the body of the original if statements had to be reindented. To make it easier
to see exactly what was changed, I've attached d5989-1a-no-whitespace.diff which was produced
by passing flags that told svn diff to ignore whitespace changes.

I've also attached before.txt and after.txt which show the decompiled class files for "SELECT
* FROM SYSIBM.SYSDUMMY1" before and after the patch. After the patch, the e1 field and the
reinit() method are not in the generated class. Also, references to the e1 field have been
replaced with null.

All the regression tests ran cleanly with the patch.
> 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:
>            Reporter: Knut Anders Hatlen
>            Assignee: Knut Anders Hatlen
>            Priority: Minor
>         Attachments: after.txt, before.txt, d5989-1a.diff, d5989-1a-no-whitespace.diff
> 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:
> 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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