Lucene 3.6, 4.x Get New Feature: Query Time Joining
Just this week, query time joining was added to Lucene 3.6, which is now preparing for a release. The main detail to take note of is the differences in the query time joining feature that will be in 3.6 and the version that was committed to the 4.0 trunk.
The version that has been committed in the 4.0 trunk is about 3 times faster than the one in 3.6. Also, the 4.0 version of this feature will support joining for fields that have multiple values for each document, but at least you will get to use the feature as early as 3.6.
This is yet another reason to prepare for a Lucene migration to 4.x when it's ready. The number of awesome new features is going to be too good to pass up.