InfluxDB tags versus fields

When writing data to InfluxDB, you have to decide which values should be tags and which should be fields.

Hint

If the value is likely to be used in a “WHERE” clause in queries, and if it has fewer than 10,000 possible values, it should be a tag.

Tags are indexed, which means you can use them as filters efficiently in InfluxDB queries.

It can be difficult to decide what should be a tag and what should be a field, but here are some guidelines:

• If it’s a value that will be aggregated and graphed over time, like the duration of a query, then it should be a field, because you’ll never be filtering on it.

• If it’s metadata like which app generated the event, then it should be a tag.

See also the official InfluxDB documentation on tags versus fields for more information.

One thing to keep in mind is that tags shouldn’t have a large number of distinct values. That could lead to a high-cardinality dataset in InfluxDB, especially when combined with other tags with many distinct values. A high-cardinality dataset could greatly increase the memory usage of the InfluxDB instance and decrease query performance across the board.

How many values is too many? There’s not a lot of concrete advice on that, and it depends a lot on other tags and the composition of the entire dataset, so let’s say 10,000 for now. This means if you have a username on an event, it can be a tag.