Made some more changes to the SortedTree implementation. Previously SortedTree would throw an exception if a duplicate entry was being added. I changed SortedTree to allow a key to point to more than one node, unless the SortedTree is created as a unique index, in which case an exception is raised when an attempt is made to add a node to an existing key entry. A SortedTree once defined as unique can not be changed to a non-unique index or vice-versa. SortedTrees now have a name, which is stored in the a property of the TREE_ROOT relationship and in the KEY_VALUE relationship (a new relationship that points from the SortedTree to the Node inserted in the SortedTree). The name of a SortedTree can not be changed. SortedTrees now store the class of the Comparator, so a SortedTree, once created, can not be used with a different Comparator. SortedTree is now an Iterable, making it possible to use it in a foreach-loop. Since there are as of yet, no unit tests for SortedTree, I will create those first before pushing my changes to Git. Preliminary results so far are good. I integrated the changes in my own application and it seems to work fine. Todo: Decide on an API for indexed relationships. (Community input still welcome).Write unit tests.Make SortedTree thread safe (Community help still welcome). Niels
> From: pd_aficion...@hotmail.com > To: user@lists.neo4j.org > Date: Mon, 4 Jul 2011 15:49:45 +0200 > Subject: Re: [Neo4j] Indexed relationships > > > I forgot to add another recurrent issue that can be solved with indexed > relationships: guaranteed unicity constraints. > > From: pd_aficion...@hotmail.com > > To: user@lists.neo4j.org > > Date: Mon, 4 Jul 2011 01:55:08 +0200 > > Subject: [Neo4j] Indexed relationships > > > > > > In the thread [Neo4j] traversing densely populated nodes we discussed the > > problems arising when large numbers of relationships are added to the same > > node. > > Over the weekend, I have worked on a solution for the > > dense-relationship-nodes using SortedTree in the neo-graph-collections > > component. After some minor tweaks to the implementation of SortedTree, I > > have managed to get a workable solution, where two nodes are not directly > > linked by a relationship, but by means of a BTree (entirely stored in the > > graph). > > Before continuing this work, I'd like to have a discussion about features, > > since what we have now is not just a solution for the dense populated node > > issue, but is actually a full fledges indexed relationship, which makes it > > suitable for other purposes too. > > An indexed relationship can for example be used to maintain a sorted set of > > relationships in the graph, that is not necessarily huge, but large enough > > to make sorting on internal memory too expensive an operation, or > > situations where only one out of a large number of relationships is > > actually traversed in most cases. > > There are probably more use cases for in-graph indexed relationships, so > > I'd like to know what features are desirable and what API would Neo4J users > > appreciate. > > P.S. I still think it would be good to consider, if technically possible, > > partitioning the relationship store per relationship type and per > > direction. The indexed relationship solution works, but is of course slower > > than a direct relationship, both with respect to insert time and traversal > > time. If dense relationships are never traversed going out of the dense > > node, the extra structure maintained by the BTree is only extra burden. > > P.P.S. If there are people with experience to make an implementation thread > > safe, please volunteer to help make the implementation production proof. > > Niels > > _______________________________________________ > > Neo4j mailing list > > User@lists.neo4j.org > > https://lists.neo4j.org/mailman/listinfo/user > > _______________________________________________ > Neo4j mailing list > User@lists.neo4j.org > https://lists.neo4j.org/mailman/listinfo/user _______________________________________________ Neo4j mailing list User@lists.neo4j.org https://lists.neo4j.org/mailman/listinfo/user
