This change merges two sections in the "Tune for search speed" documentation
that recommend mapping numeric identifiers as keywords. Both sections contain
mostly the same advice, so they can be merged.
Closes#32733
Allowing `_doc` as a type will enable users to make the transition to 7.0
smoother since the index APIs will be `PUT index/_doc/id` and `POST index/_doc`.
This also moves most of the documentation to `_doc` as a type name.
Closes#27750Closes#27751
It adds notes about:
- how preference can help optimize cache usage
- the fact that too many replicas can hurt search performance due to lower
utilization of the filesystem cache
- how index sorting can improve _source compression
- how always putting fields in the same order in documents can improve _source
compression
This moves the "Performance Considerations for Elasticsearch Indexing" blog post
to the reference guide and adds similar recommendations for tuning disk usage
and search speed.