Auto-configured JCacheMetrics cannot be customized

[wilkinsona]

See #46017 for background.

Micrometer is going to provide a setting that allows the JCache removals to be registered as a function counter. As far as I can tell, that option won't be usable in Boot as the auto-configured JCacheCacheMeterBinderProvider isn't @ConditionalOnMissingBean so there's no easy way to define your own provider with a custom JCacheMetrics that uses a function counter for removals.

A couple of options:

1. Make the auto-configured JCacheCacheMeterBinderProvider @ConditionalOnMissingBean
2. Provide a configuration property, something like management.metrics.cache.jcache.register-removals-as-function-counter, to control Micrometer's new setting.

We could do either or both of these.

[hakimrabet]

I've submitted a PR. spring-projects/spring-boot#46355. It makes JCacheCacheMeterBinderProvider overridable and add a configuration to register removals as a function counter. I'm not sure if it's exactly what you're looking for, but i'm happy to adjust it based on feedback.

[wilkinsona]

We don't know what we're looking for at the moment, hence the pending-design-work label. That design work will have to be done by a member of the core team before we can proceed.

[jonatan-ivanov]

fyi: micrometer-metrics/micrometer#6471 is released
Also, latest bits of Micrometer should prevent registering different Prometheus types with the same name: micrometer-metrics/micrometer#6470 (scrape should not fail but time series will be missing).