[jboss-dev-forums] [Design of Messaging on JBoss (Messaging/JBoss)] - Re: Journal Cleanup and Journal Compactor

[clebert.suconic@jboss.com]

This is what I have been doing on the journal compacting.


- I first need to elect what files will be compacted. This needs to be a sequential list, starting at the first file. But I can't compact a file with pending transactions as I don't know if the user will later decide for a rollback or not.


- I have created another field on the Header with a orderID. The JournalFile now has a fileID and a orderID. (fileID will be aways equals to orderID with the exception on compacting files).


- I open a file with the same orderID as the first file on the journal.
(create or open, getting it from the list of available files).

- I open a transaction on the that file, and I add a record stating that I am compacting files (with the list of fileID)

- As I read the files, I add the valid records at the compacting output. When I'm done I commit the transaction at the compacting output.

I keep opening files over demand (getting them from the available files list, or creating over demand)


- If the server crash now, I will have the compacting record stating there are files that need to be deleted (reload will handle that also)

- I now delete the old files (delete here means.. putting them back to available files).

- As soon as all the files are deleted, I can delete the compacting record within the transaction.


By using the transaction approach we already have in the journal, will simplify things, as we won't need any temporary files. 

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