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From "Stefan Guggisberg (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JCR-642) Support flat content hierarchies
Date Mon, 03 Aug 2009 12:54:15 GMT

    [ https://issues.apache.org/jira/browse/JCR-642?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12738323#action_12738323
] 

Stefan Guggisberg commented on JCR-642:
---------------------------------------

@bart;

> Would it be an idea to store the hierarchical information in a separate table with only
(node_id, parent_id)?

yes, that would be the obvious approach for db-based pm's. 

some random thoughts:
- you'd need a 3rd column ('name')
- you'd need a 4rd column (e.g. 'pos', in order to support ordered child nodes)
- read performance would suffer, especially for remote db's (2+ instead of 1 db access)
- write performance would suffer (updating/reorganizing indices of very large tables 
  can be very expensive)
- same-name sibling support would be a challenge (both implementation and performance-wise)
- Node.hasNode() e.g. would be significantly slower 

> Support flat content hierarchies
> --------------------------------
>
>                 Key: JCR-642
>                 URL: https://issues.apache.org/jira/browse/JCR-642
>             Project: Jackrabbit Content Repository
>          Issue Type: Improvement
>          Components: jackrabbit-core
>            Reporter: Jukka Zitting
>
> The current best practice with Jackrabbit is to avoid flat content structures due to
performance concerns.
> These concerns are caused by the fact that the NodeState implementation requires the
list of child node names and identifiers to be available at all times.  In fact many (all?)
current persistence managers implement this requirement by storing and loading this list as
a part of the serialized node state. When this list grows, the performance and memory overhead
of managing the list grows as well. As a side note, this also creates potential consistency
issues since the parent/child links are stored both within the child list of the parent node
and as the parent link of the child node.
> To solve this issue, I believe we need to break the tight bonding between the node state
and the list of child nodes. This will likely require major refactoring of the Jackrabbit
core, including breaking the NodeState and PersistenceManager interfaces, so I don't expect
a solution in near future. However, we should start thinking about how to best do this, and
at least be concerned about building in any more assumptions about the list of child nodes
always being readily available.

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