...

This is also a usability issue when kafka-topics is used with --describe option and no topic name is provided. We get all configurations of all the topics, where a user may only be interested in only one or few of the configurations. For kafka-topics command we also need a way to skip getting configuration so that partition information of all topics can be fetched w/o fetching their configurationconfigurations.

We need to a way to specify ConfigurationKeys parameter that DescribeConfigsResource takes to bring AdminClient::describeConfigs api to parity with DescribeConfigsResource and allow AdminClient’s users to specify configuration keys that they are interested in.

In addition we need to add same option to kafka-topics command line utility so that users of the tool don’t need to fetch all configurations when they are interested in only a few or none of them.

Public Interfaces

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

A public interface is any change to the following:

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Binary log format

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The network protocol and api behavior

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Any class in the public packages under clientsConfiguration, especially client configuration

• org/apache/kafka/common/serialization

• org/apache/kafka/common

• org/apache/kafka/common/errors

• org/apache/kafka/clients/producer

• org/apache/kafka/clients/consumer (eventually, once stable)

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Monitoring

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Command line tools and arguments

We will modify the DescribeConfigsOptions argument of the AdminClient::describeConfigs api to take an additional parameter List<String> configurationKeys, which will be same as one that the DescribeConfigsResource  takes so that AdminClient::describeConfigs users can specify configurations to fetch. An empty or null value for this will behave as it behaves today by fetching all configuration values. Here is how the new DescribeConfigsOptions structure will look like after this change:

@InterfaceStability.Evolving
public class DescribeConfigsOptions extends AbstractOptions<DescribeConfigsOptions> {

    private boolean includeSynonyms = false;
    private boolean includeDocumentation = false;
    private List<String> configurationKeys;   // This is the newly introduced field
...
...
    public List<String> configurationKeys() {
      return configurationKeys;
    }
...
...
    public void configurationKeys(List<String> configurationKeys) {
      this.configurationKeys = configurationKeys;
    }
...
}

In addition to this we propose two changes to the kafka-topics  command line tool :

1. Allow --config  option to be specified when using --describe option.  When used in such a way, only the configuration(s) specified will be fetched for the topic.
2. Add --partition-only option that when used with –describe  will skip fetching configuration of the topics and will only return partition information.

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Proposed Changes

Describe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.

Compatibility, Deprecation, and Migration Plan

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There is no compatibility issue as we are adding a new field to an existing data structure (DescribeConfigsOptions). If the field is not specified then the code will behave in same manner as existing code. The same applies to changes to the kafka-topics tool, as we are adding new options and existing options will continue to behave as is.

Rejected Alternatives

If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.