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From "Martijn Hendriks (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JCR-204) Improve recoverability
Date Sun, 21 Oct 2007 12:34:51 GMT

    [ https://issues.apache.org/jira/browse/JCR-204?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12536503

Martijn Hendriks commented on JCR-204:

The same problem applies to the cluster revision table as it is updated in a separate transaction
after the search index update. This is problematic as the crash of one clusternode may corrupt
the search indices of all other clusternodes.

I get the feeling that the persistence managers should not only apply the changes of a ChangeLog
to the persistent content, but should also store the ChangeLog itself in the same transaction.
This stored ChangeLog can then be used for recovery operations on the search index. (In order
to solve the above-mentioned problem that the SearchIndex is one step behind you only need
the last ChangeLog). I think that the clustering subsystem can be adapted for this purpose.
I.e., move the UpdateEventChannel logic currently in the ClusterNode class to the peristence
managers. Any thoughts on this?

> Improve recoverability
> ----------------------
>                 Key: JCR-204
>                 URL: https://issues.apache.org/jira/browse/JCR-204
>             Project: Jackrabbit
>          Issue Type: Improvement
>          Components: indexing, jackrabbit-core, observation, transactions
>         Environment: svn revision: 265028
>            Reporter: Marcel Reutegger
>            Assignee: Marcel Reutegger
>            Priority: Minor
> 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
> 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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