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From "Kim Haase (JIRA)" <j...@apache.org>
Subject [jira] Created: (DERBY-3612) Developer's Guide needs correction on garbage collection
Date Thu, 10 Apr 2008 15:34:05 GMT
Developer's Guide needs correction on garbage collection
--------------------------------------------------------

                 Key: DERBY-3612
                 URL: https://issues.apache.org/jira/browse/DERBY-3612
             Project: Derby
          Issue Type: Bug
          Components: Documentation
    Affects Versions: 10.3.2.1
            Reporter: Kim Haase
            Assignee: Kim Haase
            Priority: Minor


In a comment on DERBY-3585, Martin Zaun pointed out the following error:

devguide/tdevdvlp20349.dita
   - found a flatly wrong statement but did NOT correct here since
     unrelated to server shutdown authentication:
     "You cannot explicitly request that the JVM unload a class, but you
     can ensure that the EmbeddedDriver class is unloaded by using a
     System.gc() to force it to garbage collect classes that are no longer
     needed. Running with -nogc or -noclassgc definitely prevents the class
     from being unloaded and makes you unable to restart Derby in the same
     JVM."

     System.gc() is only a suggestion to the Runtime to garbage-collect, it
     cannot be enforced, and there's no guarantee whatsoever that GC has
     run and any classes been unloaded. Likewise it's most probably not
     guarantueed that -nogc or -noclassgc definitely (!) prevent a class
     from being unloaded (a JVM may ignore these options...) 

This needs to be fixed. Thanks, Martin.

One more question: are -nogc and -noclassgc java command line options, or options to some
other command? I can't find them in the java command documentation -- http://java.sun.com/javase/6/docs/technotes/tools/windows/java.html.
There is an -Xnoclassgc option, however.


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