I think I've found a bug with ElasticSearch with _mlt and node clients.

We're running 0.19.8.

We have two data nodes and each app server has its own ES instance running in node client mode. Searches and normal document GETs work fine, however when running _mlt on a client node, I get an IndexMissingException. The exact same query works fine on the data node. I suspect _mlt is only checking the local _mlt

To sum it up:

On data node:
$ curl http://localhost:9200/foo/bar/1 # Works
$ curl http://localhost:9200/foo/bar/1/_mlt # Works

On client node:
$ curl http://localhost:9200/foo/bar/1 # Works
$ curl http://localhost:9200/foo/bar/1/_mlt # Fails with IndexMissingException

Full gist showing curl verbose output at https://gist.github.com/3431254

Originally raised on group at https://groups.google.com/forum/#!starred/elasticsearch/iFGSXu1e77Q