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Date: Thu, 17 Jun 2010 07:53:26 -0400 (EDT)
From: "Jukka Zitting (JIRA)" <jira@apache.org>
To: dev@jackrabbit.apache.org
Subject: [jira] Commented: (JCR-2660) Hierarchical map-reduce
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    [ https://issues.apache.org/jira/browse/JCR-2660?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12879754#action_12879754 ] 

Jukka Zitting commented on JCR-2660:
------------------------------------

As discussed with Norman Maurer from the Apache James project, one good use case for this would be to maintain per-nodetype counts of nodes in each subtree. In James they need this information to efficiently tell the number of message nodes within a potentially huge mailbox subtree.

> Hierarchical map-reduce
> -----------------------
>
>                 Key: JCR-2660
>                 URL: https://issues.apache.org/jira/browse/JCR-2660
>             Project: Jackrabbit Content Repository
>          Issue Type: New Feature
>          Components: jackrabbit-core
>            Reporter: Jukka Zitting
>             Fix For: 2.2.0
>
>
> As discussed on a few occasions earlier, it would be great to have a feature that allows efficient and automatic processing of information over entire subtrees of content. Such a feature could be used to maintain custom reports, search indexes, and other summary information for selected subtrees.
> The map-reduce paradigm works great for such a purpose, as you can combine a per-node map operation with a reduce operation that combines the map results of the children of a given parent node. It's easy to generalize this model to cover entire subtrees. And if the reduced information is stored as a part of each parent node, it's even possible to incrementally update the results for an entire subtree when just a part of the subtree is modified.

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