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https://issues.apache.org/jira/browse/DERBY-5989?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Knut Anders Hatlen updated DERBY-5989:
--------------------------------------
Attachment: after.txt
before.txt
d5989-1a-no-whitespace.diff
d5989-1a.diff
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: 10.10.0.0
> 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:
> 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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