Improve recoverability

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:

1)

• 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

2)

• 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!