remove metric `db.client.connections.usage`

[maryliag]

When updating to only send stable DB semconv, db.client.connections.usage should be removed. Today the emission is not gated on semconv stability.
Ideally the replacement for it (db.client.connection.count) should be sent instead (on places that an experimental metric can be sent, otherwise don't sent it yet, until there is a way to opt-in for experimental)

Dependency on #3585

[Luffy-nani]

Hey @maryliag!
I took a shot at fixing this issue and opened PR #3592.

I'd love to get your feedback! Please take a look at the PR when you have a chance and let me know if there are any changes or improvements you'd like to see. Happy to iterate!

[maryliag]

hey @Luffy-nani, thank you for your interest! I added some comments to the PR, that was not quite what I was looking for with this issue. I added the dependency PR to the description, so hopefully is more clear.

For now, let's put this one on hold, until we decide clearly the next steps.

[Luffy-nani]

@maryliag Thanks for clarifying. I'd implemented it based on how the original issue described the fix (gating the metric behind the semconv opt-in), so that's where the approach came from. I'll check the updated description for the dependency PR link now that it's added.

[maryliag]

Hey @Luffy-nani , that PR is now merged, so let me know if you still want to take this issue, which would be the removal of db.client.connections.usage while also adding db.client.connection.count

[Luffy-nani]

@maryliag, Yes, Id love to take this on
I will start working on it

[Luffy-nani]

Hey @maryliag
before I start, want to confirm one thing. Looking at instrumentation-pg, it emits db.client.connection.count unconditionally (no gating behind OTEL_SEMCONV_STABILITY_OPT_IN). Should Mongo/MySQL follow that same unconditional pattern, or is there gating logic you have in mind that I should implement instead? Just want to make sure I match the right approach before diving in.

[maryliag]

You can follow the same pattern as PG and always send them