THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Status
Current state: DRAFTING
Discussion thread: here
JIRA: here
Motivation
The KafkaConsumer is a complex client that incorporates different configurations for detecting consumer failure to allow remaining consumers to pick up the partitions of failed consumers. One such configuration is max.poll.interval.ms which is defined as:
| max.poll.interval.ms | The maximum delay between invocations of poll() when using consumer group management. This places an upper bound on the amount of time that the consumer can be idle before fetching more records. If poll() is not called before expiration of this timeout, then the consumer is considered failed and the group will rebalance in order to reassign the partitions to another member. | int | 300000 | [1,...] | medium |
This scenario is typically hit when the application code to process the consumer's fetched records takes too long (longer than max.poll.interval.ms). Hitting this timeout will cause the consumer to leave the group and trigger a rebalance. The consumer will end up rejoining the group if processing time was the only issue.
Sometimes a long processing time is unavoidable if:
- Minimum processing time is long to begin with
- Processing involves talking to a downstream service which sometimes causes a long response (ex. load issues)
In such cases, the user must fine-tune the configurations to fit their use-case however detection of such events is currently difficult. The consumer will log an error when such threshold is hit:
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:
Binary log format
The network protocol and api behavior
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)
Monitoring
Command line tools and arguments
- Anything else that will likely break existing users in some way when they upgrade
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
- What impact (if any) will there be on existing users?
- If we are changing behavior how will we phase out the older behavior?
- If we need special migration tools, describe them here.
- When will we remove the existing behavior?
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.