问题
Is it better to include my own time-stamp (with milliseconds) for higher performance queries using BETWEEN look-ups based on time-stamp?
I understand from previous posts that it is represented as number of seconds since 1970. Since it is a core element I might guess it is not indexed.
回答1:
_ts is range-indexed and max precision (-1) by default in DocumentDB, unless overridden explicitly by the user. Therefore you can execute range queries against it.
That said, if you need a more granular timestamp with milliseconds, it is best to use your own higher-precision attribute. For example, you could use a timestamp as a string in the ISO 8601 format, for example - "2016-08-29T21:48:38.334", and range-index that attribute. That will serve two purposes - enable the date and time to be human readable, and execute range queries efficiently against that attribute. An example query with this timestamp attribute (named as, say, "createdTs") would then be:
SELECT r.id FROM root r WHERE
r.createdTs > "2016-08-29T21:48:38.334" and r.createdTs < "2016-08-29T21:50:00.000"
来源：https://stackoverflow.com/questions/39213819/is-ts-on-documentdb-document-indexed