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From "Daniel John Debrunner (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-2118) Change some boundary checks in ArrayInputStream to ASSERTs to improve performance
Date Wed, 29 Nov 2006 15:00:21 GMT
     [ http://issues.apache.org/jira/browse/DERBY-2118?page=all ]

Daniel John Debrunner updated DERBY-2118:

    Attachment: d2018_clearlimit_cleanup_diff.txt

patch d2018_clearlimit_cleanup_diff.txt

Patch which improves the clearLimit() method by removing the possibility that the byte array
is ever null.
Instead of using null when creating an empty ArrayInputStream an empty array is used instead.
Remove some unused methods.
Change some callers of the 2-arg setLimit() to the 1-arg setLimit() as it is more efficient.
Fix a bug where setData() would not reset the position to zero (previously it was unmodified
at a potentially invalid position)

I believe this provides a small improvement (~1%), fixes a bug and does not change the behaviour
of the class.

I have not run any tests on this change.

> Change some boundary checks in ArrayInputStream to ASSERTs to improve performance
> ---------------------------------------------------------------------------------
>                 Key: DERBY-2118
>                 URL: http://issues.apache.org/jira/browse/DERBY-2118
>             Project: Derby
>          Issue Type: Improvement
>          Components: Performance
>    Affects Versions:
>            Reporter: Dyre Tjeldvoll
>            Priority: Trivial
>             Fix For:
>         Attachments: d2018_clearlimit_cleanup_diff.txt, derby-2118.diff, derby-2118.stat,
> Profiling shows that a significant amount of CPU is spent doing boundary checking in
ArrayInputStream.setPosition() and ArrayInputStream.setLimit(). These checks appear to be
there to detect error conditions, so it seems more appropriate to make them ASSERTs. Especially
since they are so expensive.
> DTrace analysis seems to confirm that these methods get called very frequently:
> Knut Anders Hatlen wrote the following in a message on derby-dev:
> FYI, I just ran the DERBY-1961 test clients and traced them with a
> DTrace script that printed how often each method was called. For the
> join client, ArrayInputStream.setPosition() was the most frequently
> called method (43837.7 calls/tx). For the single-record select client,
> it was third (58.4 calls/tx), only beaten by Object.<init>() and
> DDMWriter.ensureLength(). I think this means that setPosition() is the
> engine method that is most frequently called, at least in read-mostly
> transactions.  ArrayInputStream.setLimit() also appeared near the top
> of the list. See http://wiki.apache.org/db-derby/Derby1961MethodCalls
> for the details.

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