Regression in v4.0.0 : Micrometer's gauges return no values for PoolStats

[ghusta]

Since v4.0.0, Micrometer's gauge metrics return no value.

For example, when using a Prometheus implementation, we will get NaN :

hikaricp_connections_active{application="my-demo-webapp",pool="HikariPool-1",} NaN
hikaricp_connections_idle{application="my-demo-webapp",pool="HikariPool-1",} NaN

I checked, there is no regression with PrometheusMetricsTracker, only with MicrometerMetricsTracker.

This kind of problem is referenced by the Micrometer documentation as :

• Why is my Gauge reporting NaN or disappearing?

At first sight, it seems to be related to this commit, which should be (partially) reverted in my opinion : 6e0f4a8

[brettwooldridge]

@ghusta This issue with that commit being the problem is that, as my linter pointed out, that private poolStats member is referenced nowhere inside of the class. So, it's removal cannot be responsible for any behavioral change. Still investigating ... possibly related to the Prometheus related changes.

Nevermind, just read the referenced link. Apparently this was fixed some time ago with a contributed commit and message Maintain strong reference to PoolStats for Micrometer gauges (#1108). Would have been nice if the code had included a comment to that effect...

[brettwooldridge]

Fixed, release publishing in ~30min.

[ghusta]

OK, thanks !