Empty result when step is larger than 300s #705
Description
Seems the commit is missing from the forked prometheus
prometheus/prometheus#9946. Therefore, there's a high chance no data can be popped when a step is larger than 300s (which is the default look back delta).
An example:
- Query params:
start=1736607436000,end=1736780236000,step=1800s - Two backends (both VM)
- Result below (both same)
value="{} =>\n0.03333333333333333 @[1736762400]\n0 @[1736764200]\n0 @[1736766000]\n0 @[1736767800]\n0 @[1736769600]\n0.03333333333333333 @[1736771400]\n0 @[1736773200]\n0 @[1736775000]\n0 @[1736776800]\n0.03333333333333333 @[1736778600]"
The overall result from the query engine was empty. I traced through the code and found data was jumped because of this, where the delta is the default value 300000.
A workaround to this is to align the start and end to step, which Grafana does. And the fact that Grafana always works while my program doesn't confused me a long time until I captured the HTTP request :(