I have an index with 2 shards and 187 segments and I would like to optimize it in order to boost performance. However, the request (_optimize?max_num_segments=1) hangs for more than 3 hours now and no change in the number of segments (senn with _cat/segments) could be observed. There is one optimize.active thread (_cat/thread_pool), but no logging whatsoever. Elasticsearch is at 13% heap usage, so I am not even sure that it is doing anything at all.
Is there something I am missing?