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From "Jukka Zitting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JCR-2170) Remove PropDefId and NodeDefId
Date Tue, 18 Aug 2009 15:27:14 GMT

    [ https://issues.apache.org/jira/browse/JCR-2170?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12744549#action_12744549
] 

Jukka Zitting commented on JCR-2170:
------------------------------------

+1 to getting rid of the DefIds. IMHO they unnecessarily bind the persisted items to specific
node type settings. Resolving the item definitions on demand makes the typing system more
flexible.

Also, I'm somewhat scared about the DefIds being essentially just hash codes of the item definitions.
What happens when we have a hash collision?

> Remove PropDefId and NodeDefId
> ------------------------------
>
>                 Key: JCR-2170
>                 URL: https://issues.apache.org/jira/browse/JCR-2170
>             Project: Jackrabbit Content Repository
>          Issue Type: Improvement
>          Components: jackrabbit-core
>    Affects Versions: 2.0.0
>            Reporter: Tobias Bocanegra
>             Fix For: 2.0.0
>
>
> the PropDefIds and NodeDefIds are used to quickly lookup a childnode- or property definition
in the nodetype registry (or effective nodetype).
> this is heavily used during reading, when calling Property.getDefinition() usually when
checking the isMultiple() flag. and of course while writing when getting the definition for
the property or childnode. 
> however, this poses problems when a nodetype is changed that is still used in the content.
if a property definition is changed due to an altered nodetype, subsequent accesses to that
property result in a "invalid propdefid" warning in the log - but the id is recomputed. this
is especially a problem when upgrade jackrabbit from 1.x to 2.0, where some of the builtin
nodetypes are defined differently.
> i think that it should be feasible to remove the propdefids and nodedefids and compute
the definition on demand. i think this can be implemented without performance loss, when some
sort of 'signatures' of the items are computed to quickly find the definitions in the effective
node type. furthermore, the most common usecase for using the property definition is probably
the isMultiple() check - which is now on the Property interface itself - which does not need
a definition lookup at all.
> and last but not least, it saves 8 bytes per item in the persistence layer.

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