[jboss-user] [JBoss Messaging] - What is the purpose of the Journal files?

[Gary Marsh]

I have a very simple program that has two classes, both generate JMS messages and both accept each others messages with onMessage() methods.  If I delete all the files that are in my data/journal directory, after startup I find that the program by default generates 400Mgs of journal files (40 files 10Mgs each).  These seem to be defined in the jbm-configuration.xml file at about lines 85 to 94, here is the snippit :

     <!-- 10 MB journal file size -->
  |       <journal-file-size>10485760</journal-file-size>
  | 
  |       <journal-min-files>40</journal-min-files>
  | 
  |       <!-- Maximum simultaneous asynchronous writes accepted by the native layer.
  |       (parameter ignored on NIO)
  |        You can verify the max AIO on the OS level at /proc/sys/fs/aio_max_nr. (aio-nr will give you the current max-aio being used)
  |       -->
  |       <journal-max-aio>5000</journal-max-aio>
  | 
  | 
  | I a curious, is this really necessary (400 MGs minimum) and what is it used for?
  | 
  | Regards,
  | 
  | GMarsh

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