[feat]PIP-410: Add a metric to track publish buffer usage.

[dao-jun]

PIP: #24028

Motivation

Add a metric to track broker side publish buffer usage.

Modifications

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

(example:)

• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

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

[lhotari]

Since Pulsar is slowly migrating to OTel for metrics, please also handle OTel for this added metric.

For metric changes, it would be useful to at least have a discussion on the dev mailing list since our PIP policy states that a PIP is required for changes in metrics.

[dao-jun]

@lhotari

Since Pulsar is slowly migrating to OTel for metrics, please also handle OTel for this added metric.

For metric changes, it would be useful to at least have a discussion on the dev mailing list since our PIP policy states that a PIP is required for changes in metrics.

Thanks for your comment. You are right, this a WIP PR, and I will do it later when I am available

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.19%. Comparing base (bbc6224) to head (3e9241b).
Report is 939 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #23751      +/-   ##
============================================
+ Coverage     73.57%   74.19%   +0.62%     
+ Complexity    32624    32385     -239     
============================================
  Files          1877     1861      -16     
  Lines        139502   144189    +4687     
  Branches      15299    16420    +1121     
============================================
+ Hits         102638   106987    +4349     
+ Misses        28908    28752     -156     
- Partials       7956     8450     +494     

Flag	Coverage Δ
inttests	26.72% <100.00%> (+2.14%)	⬆️
systests	23.14% <100.00%> (-1.19%)	⬇️
unittests	73.69% <100.00%> (+0.85%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...rg/apache/pulsar/broker/service/BrokerService.java	84.57% <100.00%> (+3.78%)	⬆️
...va/org/apache/pulsar/broker/service/ServerCnx.java	72.00% <100.00%> (-0.15%)	⬇️

... and 1054 files with indirect coverage changes

[crossoverJie]

The initial value and result are both 0, it cannot be determined whether it has taken effect?