How many shards and replicas should I have?
References:
- https://www.elastic.co/guide/en/elasticsearch/reference/6.2/_basic_concepts.html
- https://www.elastic.co/blog/found-sizing-elasticsearch
- https://www.elastic.co/guide/en/elasticsearch/reference/master/tune-for-indexing-speed.html
- https://www.elastic.co/guide/en/elasticsearch/reference/master/tune-for-search-speed.html