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From "Kristian Waagan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3731) Improve calculation of refSize in ClassSize.java
Date Fri, 06 Mar 2009 13:13:56 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3731?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12679584#action_12679584
] 

Kristian Waagan commented on DERBY-3731:
----------------------------------------

Thanks for looking at the patch, Kim.

As far as I know, several JVMs use the "sun.arch.data.model", but I also think it is an undocumented
feature of the Sun JVM. That's why it is optional, and Derby has other mechanisms to determine
the "bitness". The nice thing about the property is that it gives a definite answer if it
is present (although it can be "unknown" I think). The logic for "os.arch" depends on knowing
the architecture, and if an entry for a specific architecture hasn't been added, we can't
conclude on the bitness. In these cases, the original heuristic will be used, which isn't
working in all cases (i.e. Derby may use the wrong bitness, which affects size calculations).

I know at least some versions of the IBM JVM use "sun.arch.data.model". The IBM JVMs also
have their own version of this property: com.ibm.vm.bitmode

> Improve calculation of refSize in ClassSize.java 
> -------------------------------------------------
>
>                 Key: DERBY-3731
>                 URL: https://issues.apache.org/jira/browse/DERBY-3731
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.5.0.0
>            Reporter: Kathey Marsden
>            Assignee: Kristian Waagan
>            Priority: Minor
>             Fix For: 10.4.2.1, 10.5.0.0
>
>         Attachments: derby-3731-1a-refsize_from_properties.diff, derby-3731-1b-refsize_from_properties.diff,
derby-3731-1b-refsize_from_properties.stat, derby-3731-1c-refsize_from_properties.diff, derby-3731-2a_update_of_policy_template.diff,
derby-3731-3a-doc_changes.diff, DERBY-3731_diff.txt
>
>
> java/engine/org/apache/derby/iapi/services/cache/ClassSize.java has a static code block
which calculates the size of a reference for the architecture.  This code could be improved
by adding garbage collection before measuring memory, to give a consistent  reading.     Also
there have been suggestions that we use os.arch or sun.arch.data.model to make the measurement
more reliable, especially on 64bit machines.

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