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From "Marcel Reutegger (JIRA)" <j...@apache.org>
Subject [jira] Created: (JCR-204) Improve recoverability
Date Wed, 31 Aug 2005 13:08:05 GMT
Improve recoverability

         Key: JCR-204
         URL: http://issues.apache.org/jira/browse/JCR-204
     Project: Jackrabbit
        Type: Improvement
  Components: core, observation, query  
 Environment: svn revision: 265028
 Reporter: Marcel Reutegger
 Assigned to: Marcel Reutegger 
    Priority: Minor
     Fix For: 1.0

Transactions in Jackrabbit are committed in SharedItemStateManager.store(). While the call
to PersistenceManager.store() is by its definition atomic, updates on the index through synchronous
notification by the ObservationManager are not. Consequently, it may happen that the index
is not up-to-date with the workspace data in case of a crash.

Consider the following cases:

- changes in a ChangeLog are successfully stored by the persistence manager
- the observation manager notifies the query handler about the change
- the query handler starts to update the index
- system crashes

-> the index is missing some changes

- changes in a ChangeLog are successfully stored by the persistence manager
- system crashes

-> the index is missing all changes

To prevent situations like 1) the index must be fully transactional implementing ACID properties.
In case an index update cannot be completed, the index will appear as if the update never
happened. Which results in a situation described in example 2)

To prevent situations like 2) the observation manager musts keep track of transactions and
make sure that committed transactions (the ones that successfully stored the changes in the
persistence manager) successfully notify all listeners. If the system should crash while listeners
are notified the events must be re-delivered on restart.

comments and suggestions on alternatives are welcome!

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