Description of available operation types in the docs

[Erni]

Hello,
I see in the docs the description of operations like this:

operation-type (mandatory): Type of this operation. Out of the box, Rally supports the following operation types: index, force-merge, index-stats, node-stats and search

However there is no description of each type. I would like to know what "force-merge" is, for example. I can figure it out from the name, but in any case the description of each type of operation should be provided.