Optimize regexp on single tag values

[kostasb]

Queries matching a single tag value using regexp :

SELECT myaggregation(myfield) FROM "mymeasurement" WHERE mytag =~ /^mytagvalue$/ AND time > now() - 15m

can be optimized to work on a direct tag match instead:

SELECT myaggregation(myfield) FROM "mymeasurement" WHERE mytag = 'mytagvalue' AND time > now() - 15m

E.g. it is possible for Grafana to generate such queries when selecting a single value from a template (e.g. tag values as templates) because regexps are available in the query editor.

InfluxDB could detect =~ /^foo$/ and rewrite that to = 'foo' and turn the linear scan into an index lookup.