Can I divide a derivative of a field with the values of another filed?

1

Hello,

I am using derivative to calculate the delta between two samples. This calculates the bytes/sec. However I want to display the B/s per subscriber. I tried to divide by a field that shows the number of subscribers but Grafana doesnt like it.

SELECT (derivative(“downlinkBytes”, 5m))/“defaultbearersActive” FROM “apnstatistics” WHERE “apn” =~ /^$APN$/ AND “host” =~ /^$GGSN$/ AND $timeFilter

2

Unfortunately InfluxDB doesn’t support math across series (yet). I know it’s something they’re working on, and consider important. You can see the issue, which is one of the most commented: https://github.com/influxdata/influxdb/issues/3552

If this is a critical feature for you, you have two choices: (1) Wait for InfluxDB to add the feature; or (2) Use a TSDB that allows math across series, like Graphite or Prometheus.

Hope this helps!

3

Hello, they are from the same series. The problem seems to be that one is an aggregation and the other a raw field. How can I overcome this?

InfluxDB Error Response: error parsing query: binary expressions cannot mix aggregates and raw fields

4

Hello,

The solution was not to use a raw field. In order to do that i had to use the mean of the measurements. Why is that though?

SELECT derivative(mean(“downlinkBytes”), 1s)/mean(“defaultbearersActive”) FROM “apnstatistics” WHERE “apn” =~ /^$APN$/ AND “host” =~ /^$GGSN$/ AND $timeFilter GROUP BY time($interval)