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From Apache Wiki <wikidi...@apache.org>
Subject [Jackrabbit Wiki] Update of "Clustering" by MartijnHendriks
Date Thu, 12 Nov 2009 09:54:52 GMT
Dear Wiki user,

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The "Clustering" page has been changed by MartijnHendriks.
The comment on this change is: Added dcumentation about the journal cleaner task.


  === Removing Old Revisions ===
- The revisions are kept in the journal except when using the Janitor - see http://issues.apache.org/jira/browse/JCR-1087
+ The journal in which cluster nodes write their changes can potentially become very large.
+ By default, old revisions are not removed. This enables one to add a cluster node
+ without much work: the new cluster node just replays the journal to get up to date (of course,
+ if the journal contains data from two years of work then this might take a while...)
+ As of Jackrabbit 1.5 there is the possibility to automatically clean the database-based
+ The local revision counter is automatically migrated to a new table in the database called
+ LOCAL_REVISIONS. To support a proper migration the "revision" parameter must be present
in the
+ configuration. After the migration it can be removed.
+ The clean-up task can be configured with three parameters:
+  * '''janitorEnabled''' specifies whether the clean-up task for the journal table is enabled
(default = false)
+  * '''janitorSleep''' specifies the sleep time of the clean-up task in seconds (only useful
when the clean-up task is enabled, default is 24 hours)
+  * '''janitorFirstRunHourOfDay''' specifies the hour at which the clean-up task initiates
its first run (default = 3, which means 3:00 at night)
+ The current solution has three known caveats:
+  * If the janitor is enabled then you loose the possibility to easily add cluster nodes.
(It is still possible but takes detailed knowledge of Jackrabbit.)
+  * You must make sure that all cluster nodes have written their local revision to the database
before the clean-up task runs for the first time because otherwise cluster nodes might miss
updates (because they have been purged) and their local caches and search-indexes get out
of sync.
+  * If a cluster node is removed permanently from the cluster, then its entry in the LOCAL_REVISIONS
table should be removed manually. Otherwise, the clean-up thread will not be effective.
+ Related issue: http://issues.apache.org/jira/browse/JCR-1087
  === Journal Type ===

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