[SOLR-17276] Use fixed rate instead of fixed delay in prometheus-exporter

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 9.7
• Component/s: contrib - prometheus-exporter
• Labels: pull-request-available
• Assignee: Unassigned
• Reporter: Rafał Harabień
• Created: 06/May/24 16:19
• Updated: 25/Oct/24 17:18
• Resolved: 03/Aug/24 04:56

Description

Prometheus-exporter is supposed to read metrics from Solr servers every 60 seconds (scrape interval can be changed using --scrape-interval argument). But the truth is it does it every 60+X seconds where X is the time needed to read metrics from all Solr servers. In my case X is 1-2 s. If Prometheus scrapes the exporter every 60 seconds it can lead to duplicated samples (e.g. metrics will stay the same for 2 minutes).

It's result of using scheduler.scheduleWithFixedDelay instead of 
scheduler.scheduleAtFixedRate.

Note: function scheduled with scheduleAtFixedRate can still be started late if previous execution has not finished. There is no risk of overlapping executions.

I am going to prepare a PR.

Issue Links

• links to: GitHub Pull Request #2442