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From Angela Schreiber <anch...@adobe.com>
Subject Re: Detecting move operations in node state diffs
Date Thu, 17 Oct 2013 14:29:48 GMT
IMHO it's worth trying to get a solution for this.

if we do, i would suggest that we detect the move before
passing the information down to the commit hooks. in other
words, there should be a method like nodeMoved in order to prevent
that every move-sensitive hook has to write the same code in order
to find out about potential moves.

kind regards
angela

On 10/17/13 2:16 PM, "Michael Dürig" <mduerig@apache.org> wrote:

>
>Hi,
>
>Currently we can't detect a move operation through diffing node states.
>Those operation are currently seen as separate remove and add operations
>that can't be easily associated with each other. This impacts permission
>evaluation (OAK-710, OAK-783) and observation (OAK-144, OAK-1090), which
>both don't have the same support for moves as had Jackrabbit 2.
>
>As discussed several times before it is not possible to regain move
>operation from simply diffing node states. We need additional
>information. One option is to annotate nodes (*) as they are moved with
>their source path. With that we could detect whether an added node was
>the target of a move operation and if so where the source of that
>operation was. However, this comes with a performance penalty since such
>a diff operation could not be done in a single pass any more. In order
>to decide whether a deleted node has been moved, the corresponding add
>needs to be found first. In essence this requires the diff operation to
>do two passes: the first one for detecting move operations and the
>second one for the other operations.
>
>To avoid the second pass, we could also remember the paths of the moved
>nodes in a global place (*). This would allow us to look up whether a
>deleted node was moved (opposed to deleted) as we go and detect moved
>nodes as soon as we come across an added node that has a source path
>annotation. As an added benefit this approach allows us to detect
>whether there was a move at all simply by checking whether there are
>entries in this global place. If this is not the case, we could fall
>back to a simpler diff mechanism.
>
>(*) All such annotations would happen as hidden items in transient space
>and would have to be removed again by some hook before persisting.
>
>WDYT, is this worth the trouble?
>
>Michael


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