Removal API or more granular idle_timeout

[thedodd]

• It would be great to have an API exposed where users could remove registered metrics by name + labels.
• Additionally, if there were a more granular idle_timeout config, such as the ability to auto-remove metrics bearing specific labels, or excluding specific labels, that could also be quite beneficial.

My immediate use case requires the first. The second is mostly convenience.

PS
Thanks for all of the excellent work on this project! I was quite relieved when I found it.

[tobz]

First off, you're welcome! Glad you've found this project helpful/useful.

Overall, a removal API would be nice and I can understand where you're coming from. The biggest issue is that this would essentially have to be implemented at the exporter-level as things stand right now, which means a lot of code duplication for each exporter.

At a high level, "exporters" provide the implementation of the Recorder trait, which is what sits behind all of the macros in terms of registration and emission of metrics. Due to this structure, exporters end up being responsible for both holding metrics and doing any necessary transformations, sending downstream, etc.

We've added a lot of power user knobs/features to the Prometheus exporter, so adding this capability to it wouldn't necessarily be out of the ordinary... although we're beginning the stretch the goal for the project, which is to provide composable building blocks.

If this is a feature you'd be willing to PR for the Prometheus exporter, I'd definitely be up for reviewing it, but I can't really think of a natural design to provide this generically, and don't have the time to work on coming up with such a design in the short term.