ES 2.3.3 Force merge not merging?

Unfortunately we've seen that force merges can take hours to complete.

There also doesn't appear to be good progress or status tracking of the merge.

I just posted about this here

Another thing to watch out for is that apparently merges are not throttled and can consume many resources on a node which we have seen (ref: https://www.elastic.co/guide/en/elasticsearch/guide/current/merge-process.html#CO41-1)