Hi,
Over at the sandbox [1] I implemented a new (AFAIK) approach for the JCR
transient space. The gist of it is in the ChangeTree class [2] while
some more Microkernel specific things are factored out into the
TransientSpace class [3].
The key idea is to only store changes to the node hierarchy in the
ChangeTree and to do that in a way which allows reconstructing a list of
corresponding operations (add, remove, move for nodes and set for
properties) from that ChangeTree. This differs from other
implementations where the list of operations is kept *together* with the
modified hierarchy. Furthermore with the ChangeTree approach no
untouched nodes need to be kept in memory. Finally the list of
operations reconstructed from a ChangeTree is minimal. That is, all
cancelling operations are reduced as much as possible: add followed by
remove of the same item results in no operations, add followed by move
of the same node results in the node being added at the target of the
move, move followed by remove of a node results in the node being
removed at the source of the move and move followed by another move of a
node results in a single move from the original source to the eventual
target. More details are in the class comment of ChangeTree and even
more details in the implementation ;-)
Michael
[1] http://svn.apache.org/viewvc/jackrabbit/sandbox/jackrabbit-microkernel/
[2]
http://svn.apache.org/viewvc/jackrabbit/sandbox/jackrabbit-microkernel/src/main/java/org/apache/jackrabbit/state/ChangeTree.java?view=markup
[3]
http://svn.apache.org/viewvc/jackrabbit/sandbox/jackrabbit-microkernel/src/main/java/org/apache/jackrabbit/state/TransientSpace.java?view=markup
