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Status

Current state:  Under Discussion Accepted

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

Voting thread: here

JIRA: KAFKA-6733

PR: #9099 (based on #4807)

Motivation

ConsoleConsumer (kafka-console-consumer) is a very important debugging tool in Kafka. However, currently it cannot print offset, partition and headers of a Kafka record. So, during debugging session, if we need to know those information, we have to use kafka-dump-log, which require file system access to the Kafka broker hosts, or use custom application, like kafkacat. This KIP is proposing to rectify this issue.

Currently, without any extra property, ConsoleConsumer prints the value of the record.

And the following properties is one of the main debugging tools used by Kafka users. Especially for new users and new setups. However, not all possible message attributes are accessible using it.
Currently we have following parameters which control the ConsoleConsumer output format:

• print.timestamp
• print.key
• print.value
• print.partition
• key.separator
• line.separator
• key.deserializer
• value.deserializer

So As you see, there is no way to print message offset, partition and headers. Also, there is no easy way to differentiate null value or blank string.

Public Interfaces

Add extra parameters to DefaultMessageFormatter which will enrich current functionality:

New properties to DefaultMessageFormatter which can be specified in kafka-console-consumer command line arguments with --property argument.

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Example output:

$ kafka-console-consumer.sh --bootstrap-server localhost:9092 --topic test --from-beginning --property print.partition=true --property print.key=true --property print.timestamp=true --property print.offset=true --property print.headers=true --property key.separator='|'

CreateTime:1592475472398|Partition:0|Offset:3|h1:v1,h2:v2|key1|value1
CreateTime:1592475472456|Partition:0|Offset:4|NO_HEADERS|key2|value2

Proposed Changes

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Add new properties to DefaultMessageFormatter as per the above:

• print.offset
• print.headers
• header.separator
• headers.deserializer
• null.literal

Compatibility, Deprecation, and Migration Plan

KIP-431 introduces incompatibility when "print.partition=true" (this property exists in the code before KIP-431 but not documented). Before KIP-431, "kafka-console-consumer" prints the partition as a number after the value for example: "key1|value1|0". After this KIP, "kafka-console-consumer" prints the partition number prefixed with "Partition:" before the key (if printed) and value, for example: "Partition:0|key1|value1" . Because this property was not documented, no migration plan is implemented in KIP-431.

The other changes are backward compatible . If a user won’t because they do not exist before. Apart from "print.partition=true", if a user does not use any new parameters, then the output of console consumer will look the same as before.

Rejected Alternatives

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• Use kafka-dump-log command to get these information. Rejected because this requires file system access to the Kafka broker's log.dirs, which is not secure.
• Use other console consumer application to access these information. Rejected because Kafka brokers may run in airtight environment or as containers, preventing us from installing other applications than the one coming with Kafka brokers.