This commit adds time support to SHOW TAG VALUES. Time can be used as
both a lower and upper boundary. However, there are some caveats.
For the `inmem` index, filtering by time will still return all results
because the index data is shared across shards.
For the `tsi1` index, filtering by time will only work down to the shard
lever. Specifically, when querying by time all shards within that time
range will be used to generate the results.
When a meta query does not include a time component then it can be
answered exclusively by the index. This should result in a much faster
query execution that if the TSM engine was engaged.
This commit rewrites the following queries such that they make use
of the index where no time component is present:
- SHOW MEASUREMENTS
- SHOW SERIES
- SHOW TAG KEYS
- SHOW FIELD KEYS
Ben Johnson
Edd Robinson
Stuart Carnie