[DERBY-3612] Developer's Guide needs correction on garbage collection

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 10.3.2.1
• Fix Version/s: 10.4.2.0, 10.5.1.1
• Component/s: Documentation
• Assignee: Camilla Haase
• Reporter: Camilla Haase
• Created: 10/Apr/08 15:32
• Updated: 04/May/09 18:22
• Resolved: 05/Aug/08 18:35

Description

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.