[feature][client] PIP-184: Topic specific consumer priorityLevel

[nahguam]

Resolves #16481

Motivation

The Pulsar Java consumer supports setting a priority level for priority message
dispatch in shared subscription consumers and priority assignment in failover
subscription consumers. See the ConsumerBuilder.html#priorityLevel(int)
Javadoc
for a detailed functional description. The Pulsar Java consumer also supports
consuming from multiple topics. However, it is not possible to set a different
priority level for different topics in the same Consumer instance.

This behaviour is desirable in some use cases. For example, a consumer
processing region specific topics might wish to configure region stickiness - A
multi-region application might be consuming from topics events-us-east-1 and
events-eu-west-1. Consumers in all regions should be configured to consume all
topics to ensure data completeness. However, to ensure low latency, the
us-east-1 consumer would need to set a higher priority level for the us-east-1
topic. Similarly, the eu-west-1 consumer would need to set a higher priority
level for the eu-west-1 topic.

Without the ability to configure different priority levels for different
topics, the developer would have to create multiple consumer instances and have
to manage the consumption from them in their application code. This feature
provides developer convenience to keep application code the same regardless of
whether this is a requirement or not.

Modifications

Introduce new methods and configuration to support setting different priority levels for different topics in the same consumer instance.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

(example:)

• Unit test ConsumerImplTest.testTopicPriorityLevel() verifies the functionality.

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

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): (no)
• The public API: (yes)
• The schema: (no)
• The default values of configurations: (no)
• The wire protocol: (no)
• The rest endpoints: (no)
• The admin cli options: (no)
• Anything that affects deployment: (no)

Documentation

Check the box below or label this PR directly.

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• doc-not-needed
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• doc
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  (Docs have been already added)

[Technoboy-]

@nahguam Could you fix the checkstyle issue?

[mattisonchao]

Look to me. I left some minor questions to hope you can answer.

[mattisonchao]

I'm unsure if adding the test coverage to actual usage is necessary. I mean to create the consumer with different priorities and then consume messages from the broker. Not just test the client configuration.

[mattisonchao]

@nahguam Could you please take a look failed test?

[nahguam]

I'm unsure if adding the test coverage to actual usage is necessary. I mean to create the consumer with different priorities and then consume messages from the broker. Not just test the client configuration.

I would hope there are already tests to verify the priority level behaviour. This only changes how the priority level is wired in from the configuration. I added a test to ConsumerImplTest to verify the wiring.

[Technoboy-]

@nahguam
There seems a failure test related to this change, could you help check it ?
https://github.com/apache/pulsar/runs/7571444716?check_suite_focus=true

[codelipenghui]

The PR can only merge after the proposal is closed https://lists.apache.org/thread/08olgc0bjr13ld3g0hz58p1sj9c4pk98

[codelipenghui]

@nahguam Please help fix the check style, so that we can merge this PR.