[jboss-user] [JBossCache] - Re: Please vote for your favorite issues -- mine :-)

[genman]

Thanks for your support.

Regarding your suggestion about functors: I'm actually thinking that something akin to a materialized view would be almost better. I may have the SQL terminology wrong, but the idea is that you take a query and then map the results to a table. When the underlying data is changed, then the results are updated.

The idea is that once you get your initial results, you would attach node listeners to the tree (perhaps just a region) and the results would be updated. In a case of a sorted query, the sorted data would be updated then.

I think this would probably be the best of both having an ordered result and what you speak of. You'd effectively have O(1) performance. The only negative consequence is that performance would be less.

I guess the implementation would be something like this:


  | public CacheQuery {
  |   void evaluate(Node n);
  |   Node getResultRoot();
  |   void close();
  | }
  | 

The queries would run against a region, not the whole tree. The key would be the "close" method that detaches the listener from the region when done. The problem is, how do you deal with all the locking and things like node removals?

If you are curious, though, I actually got a POJO TreeMap implemented using the OrderedNode. I can send the patches to you to look at.  Though I do agree that it would almost be better to have a query language. I tried getting a TreeSet done, but it's actually very difficult as it's almost impossible to write a comparator for a Map's value. (You can try as an exercise.) What I would end up doing is keeping two trees around.

As for per-node expiration (removal), I believe that my implementation is "hacky" but doesn't impact the rest of the core code. If there is sufficient interest, it might be best to integrate it as a more developed feature.


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