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From "Daniel John Debrunner (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-2118) Change some boundary checks in ArrayInputStream to ASSERTs to improve performance
Date Tue, 28 Nov 2006 01:37:21 GMT
    [ http://issues.apache.org/jira/browse/DERBY-2118?page=comments#action_12453774 ] 
            
Daniel John Debrunner commented on DERBY-2118:
----------------------------------------------

I'm also close to -1 on this change. The setLimit() call comes from Limit which prescribes
its api, and the modified implementation does not fulfill its contract.

The discussion on the list has:

> I have noticed that two methods, setPosition(int) and setLimit(int)
> seem to use more CPU than what I find "reasonable" given what they're
> supposed to do. Together they use 4.5% of user CPU and 1.5% of system
> CPU. 

Are there updated numbers for the same tests with the patch applied?

Also how can these methods take up 1.5% of system time, since they are just modifying instance
fields, isn't that all user code?

> 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: 10.2.1.6
>            Reporter: Dyre Tjeldvoll
>            Priority: Trivial
>             Fix For: 10.3.0.0
>
>         Attachments: derby-2118.diff, derby-2118.stat, derby-2118.v2.diff
>
>
> 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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