[improve][client] Client add permits metric

[crossoverJie]

Motivation

Added a new dimensional metric to help better monitor clients.

Modifications

Add pulsar.client.consumer.available_permits.count metric.

Verifying this change

• Make sure that the change passes the CI checks.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: crossoverJie#23

[crossoverJie]

@merlimat @asafm PTAL.

[asafm]

If you copied from above you need to notice .count was added since there are two sub-metrics for receive_queue. In yours you only have one.
Also, thinking about available. Maybe if we know the limit:

pulsar.client.consumer.permit.remaining
pulsar.client.consumer.permit.limit

if we don't know the limit then maybe just ``pulsar.client.consumer.permits.remaining`

See naming guidelines here https://opentelemetry.io/docs/specs/semconv/general/metrics/

[crossoverJie]

If you copied from above you need to notice .count was added since there are two sub-metrics for receive_queue. In yours you only have one.

I noticed that .size is the data of the message body, but permits is just a counter and does not have a size itself, so .size may not be needed.

---

Also, thinking about available. Maybe if we know the limit:

pulsar.client.consumer.permit.remaining pulsar.client.consumer.permit.limit

pulsar.client.consumer.permit.remaining= getCurrentReceiverQueueSize() / 2- available

pulsar.client.consumer.permit.limit= getCurrentReceiverQueueSize() / 2

Do you mean this?

[asafm]

Yes.

Also I didn't write that size is needed :) Only that we don't need .count and added suggestion how to name it.

[crossoverJie]

Thank you for your follow-up, the changes have been made.

PTAL.