Scraper fails on prometheus NaN metrics

[andig]

Steps to reproduce:

1. Add a scrape target the has NaN values
2. Scrape it

Expected behavior:
No errors

Actual behavior:
Log file:

ts=2022-04-21T06:05:39.347453Z lvl=error msg="Unable to marshal json" log_id=0_zV5qh0000 error="json: unsupported value: NaN"

At this point, no metric is collected.

It seems this behaviour has recently been introduced with the prometheus golang library in 1.12.1: prometheus/client_golang#981. According to spec (see that issue), NaN is a value.

A previous issue for Inf values was fixed in #10490.

Environment info:

InfluxDB 2.0.9
Server: d1233b7
Frontend: 9c89e22

May be related to #4089

[andig]

No feedback? This would impact anyone scraping prometheus metrics produced by a recent prometheus library?

[Sniper91]

influxdb don't support NaN by design.
When encoding float value, it uses NaN as a sentinel to mark the end of data block.
https://github.com/influxdata/influxdb/blob/master/tsdb/engine/tsm1/float.go

[andig]

influxdb don't support NaN by design.

...and that exactly is the problem when using Influx to scrape prometheus. It seems though, that prometheus has reverted the change for enabling NaNs.