I have data being inserted that uses host names. Annoyingly I'm about to change a domain from .lan to .mydomain.com
Obviously I'd like to be able to search my historical data of a machine as it crosses this change.
Can I update a tag definition from machine.lan to machine.mydomain.com?
Answer
While @Michael's answer is correct in that you can't change tag values via InfluxDB commands, you can however write a client script that can change the value of a tag by inserting "duplicate" points in the measurement with the same timestamp, fieldset and tagset, except that the desired tag will have its value changed.
Point with wrong tag (in Line Protocol format):
cpu,hostname=machine.lan cpu=50 1514970123
After running
INSERT cpu,hostname=machine.mydomain.com cpu=50 1514970123
a SELECT * FROM CPU would include
cpu,hostname=machine.lan cpu=50 1514970123
cpu,hostname=machine.mydomain.com cpu=50 1514970123
After the script runs all the INSERT commands, you'll need to drop the obsolete series of points with the old tag value:
DROP SERIES FROM cpu WHERE hostname='machine.lan'
Of course, this is highly inefficient (note in particular this bug) and if you need to update a tag value to another tag value that other points you don't want to drop already have, you can't just DROP SERIES. So please vote for InfluxDB to implement tag renaming and in particular, changing tag values based on WHERE queries. Or consider an alternative time-series database that lets you use regular SQL, such as Timescale.