There are two new metrics,
rule_group_last_evaluation_samples will help you track expensive rule groups and
prometheus_tsdb_data_replay_duration_seconds will provide the how long the WAL replay took at startup.
The deprecated v2 API has been removed, as this was mainly gRPC based and causing maintenance problems. In the very unlikely that you were using it you should switch to the v1 API.
There have been improvements to the new UI on the alerts and targets page, making it more obvious what the current view settings are and allowing collapsing scrape configs respectively.
Prometheus 2.18 switched to Go 1.14 which included a performance regression which has a significant effect on block size. A temporary workaround was added in this release, which involves making scrape timestamps slightly less accurate.
There’s also a number of improvements, bug fixes and other changes, see the release notes for more detail.
Wondering how to upgrade? Contact us.