Unnecessary performance overhead in MongoMK's calculation of keys for the nodeCache, nodeChildrenCache

The key of MongoMK.nodeCache and nodeChildrenCache is currently a String, whose evaluation is somewhat expensive:

path + "@" + rev

In the above code, "rev.toString()" internally creates another StringBuilder to generate another intermediate string. The attached screenshot shows that around 5% of profiling time within "MongoMK.getNode()" is wasted in order to calculate the caching key. Other methods are also affected.

A simple way to improve this is to reuse a single StringBuilder for the key, as such:

StringBuilder sb = new StringBuilder();
sb.append(path);
sb.append("@");
rev.appendTo(sb);

A better way would probably be to wrap "path" and "rev" in another re-usable "NodeRev" object to be used instead of using two references "path" and "rev". The "NodeRev" object would provide appropriate equals() and hashCode() implementations.