I read the documentation about the distributed search execution of elasticsearch: https://www.elastic.co/guide/en/elasticsearch/guide/current/distributed-search.html
... and I was wondering if these query and fetch phases are principles of map/reduce in it's abstract sense?
For example the query phase:
map-phase: search request execution on primaries and replicas of every shard in index. Temporary result of a local sorted priority queue.
reduce-phase: Every shard returns the docIDs to the coordinating node. Coordinating node merges the results
to one final result.
So is it fair to say, that elasticsearch uses map/reduce-Algorithms internally? And if so, are there other functionalities like reindexing which use map/reduce?