[improve] [broker] Add subscription prefix for internal reader

[hangc0276]

Fixes #xyz

Main Issue: #xyz

PIP: #xyz

Motivation

We have many system topics, such as

• __change_events
• __transaction_buffer_snapshot
• __transaction_buffer_snapshot_indexes
• __transaction_buffer_snapshot_segments
• transaction_coordinator_assign
• _transaction_log
• __transaction_pending_ack

In Pulsar Broker, we create an internal reader to fetch messages from those system topics. Due to we do not specify the subscription prefix, the reader will generate a random subscription name for each reader.

In PIP-355, we introduced a broker-level metric named pulsar_broker_out_bytes_total, which separate the system subscription traffic bytes and user subscription traffic bytes. Due to the internal readers don't have a subscription prefix, we group the internal reader's traffic bytes into user subscription traffic.

Modifications

In this PR, we introduce a system subscription prefix named __system_reader and group the internal reader's traffic into system subscription traffic bytes in metric pulsar_broker_out_bytes_total.

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

PR in forked repository:

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 62.50000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 73.40%. Comparing base (bbc6224) to head (1fea1e3).
Report is 468 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #23044      +/-   ##
============================================
- Coverage     73.57%   73.40%   -0.17%     
- Complexity    32624    33493     +869     
============================================
  Files          1877     1917      +40     
  Lines        139502   144067    +4565     
  Branches      15299    15741     +442     
============================================
+ Hits         102638   105752    +3114     
- Misses        28908    30190    +1282     
- Partials       7956     8125     +169     

Flag	Coverage Δ
inttests	27.48% <50.00%> (+2.90%)	⬆️
systests	24.80% <37.50%> (+0.47%)	⬆️
unittests	72.46% <62.50%> (-0.39%)	⬇️

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

Files	Coverage Δ
...sar/broker/service/persistent/PersistentTopic.java	79.21% <100.00%> (+0.75%)	⬆️
...roker/systopic/TopicPoliciesSystemTopicClient.java	72.50% <100.00%> (+0.34%)	⬆️
...ransactionBufferSnapshotBaseSystemTopicClient.java	76.62% <100.00%> (+0.30%)	⬆️
.../apache/pulsar/common/naming/SystemTopicNames.java	77.77% <ø> (ø)
...oker/service/nonpersistent/NonPersistentTopic.java	71.31% <0.00%> (+1.84%)	⬆️

... and 503 files with indirect coverage changes

[Technoboy-]

LGTM, do we need a PIP for this ?

[hangc0276]

LGTM, do we need a PIP for this ?

@Technoboy- It doesn't change any interface or configurations, and I think we do not need a PIP