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From "Jukka Zitting (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (JCR-2968) Add an option to read the Clustering Journal from a different source than the rest of the clustering info
Date Thu, 06 Oct 2011 15:06:30 GMT

     [ https://issues.apache.org/jira/browse/JCR-2968?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Jukka Zitting updated JCR-2968:

    Attachment: 0001-JCR-2968-Add-an-option-to-read-the-Clustering-Journa.patch

OK, I see why this would be useful, but I think the implementation is a bit confusing.

The point, if I understand correctly, is to update the LOCAL_REVISIONS table on the master
database, but use the replicated slave database for everything else. Thus to me it would feel
more natural if it was the data source for the LOCAL_REVISIONS table instead of all the other
access that's configured with an extra new parameter.

Also, it seems that we should have some explicit flag to enforce the read-only requirement
of such deployments.

The attached patch implements these suggestions by introducing a "localRevisionDataSourceName"
configuration option and an explicit "readOnly" flag to accompany it. The read-only status
is automatically set if a local revision data source is specified. A read-only journal will
throw exceptions for any write attempts on that cluster node.

Would this work for your use case?
> Add an option to read the Clustering Journal from a different source than the rest of
the clustering info
> ---------------------------------------------------------------------------------------------------------
>                 Key: JCR-2968
>                 URL: https://issues.apache.org/jira/browse/JCR-2968
>             Project: Jackrabbit Content Repository
>          Issue Type: New Feature
>          Components: clustering, jackrabbit-core
>            Reporter: Christian Stocker
>             Fix For: 2.3.1
>         Attachments: 0001-JCR-2968-Add-an-option-to-read-the-Clustering-Journa.patch,
> This patch adds the possibility to read (but not write) the Cluster JOURNAL from a different
source than the rest of the cluster information. This makes it possible to setup a master/slave
DB setup, where everything cluster related is read from the slave, but writes to the master.
It reads the actual data also from the slave and assumes that this jackrabbit instance never
does any writes (except for updating the cluster index position in the DB). We have to read
the Cluster Journal from the slave to guarantee a consistent state
> More info why and how is here
> http://blog.liip.ch/archive/2011/05/04/how-to-make-jackrabbit-globally-distributable-fail-safe-and-scalable-in-one-go.html
> I didn't write any tests yet, if you can point me, where I should add them, I'll gladly
do them.
> Would be great, if we could integrate that in any of the future Jackrabbit releases.
> It's of course fully backwards compatible, nothing changes, if you don't sepcify 
>  <param name="dataSourceNameJournalRead">
> in repository.xml

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