0.19.10 is out. You can download it here. It contains several bug fixes but also new features, including:
has_parent filter allows to execute a query on parent documents and result in matching children documents (the inverse of
has_child). More info here. Also, the performance of
has_child filter/query has been greatly improved.
Less overhead of filter cache
The filter cache cleanup process is now more optimized, specially when large number of shards exists on a node.
Cluster Reroute API
The cluster reroute API allows to explicitly send commands that would move, cancel, and allocate shards. Note, this is an experimental API and feedback is welcomed.
The Bulk UDP interface allows to have elasticsearch listen using UDP for bulk formatted requests. While UDP comes with its own downsides, it can come in handy, specially when indexing non critical data (ala statsd). This interface is also experimental.