Status

Current state: Under Discussion

Discussion thread: here

JIRA: KAFKA-1660

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Current KafkaProducer.close() method will try to finish sending all pending messages before it returns. There are several motivations to add a close method with timeout in the producer.

1. Sometimes, user will want to close a producer wiithin a bounded time to avoid blocking on producer.close() for too long.
2. One specific use case of 1) is that in some scenarios, user will want to close the produce immediately and fail all the unsent messages in RecordAccumulator. Some examples are:
   1. In mirror maker, if a send failed, we don't want to continue sending messages in RecordAccumulator to avoid reordering.
   2. For people who are using deployment tools, a service is expected

So we need to provide an interface that allow user to choose to close producer in which way.

Public Interfaces

Add another interface:

public void close(long timeout, TimeUnit timeUnit)

This call waits some specified time for the producer to close. If the producer did not finish closing before timeout, it close the producer forcefully by failing all the unsent messages.

• close(-1, TimeUnit.MILLISECONDS) - do not wait, fail all the incomplete requests and close the producer.
• close(0, TimeUnit.MILLISECONDS) - wait until all the messages are either sent successfully or failed
• close(10000, TimeUnit.MILLISECONDS) - wait at most 10 seconds for the producer to send pending messages, if messages cannot be sent in 10 seconds, fail the rest of messages and close producer.

Several addition considerations:

• The close(timeout) should work when called from a user caller thread or the internal sender thread.
• In sender thread only close(-1, TimeUnit.MILLISECONDS) should be called because:
  
  • close() or close(0, TimeUnitMILLISECONDS) should not be called because that will make producer block forever.
  • close(500, TimeUnit.MILLISECONDS) has the same effect as close(-1, TimeUnit.MILLISECONDS) only except it will block for 500 milliseconds.
• Because it is possible the close(timeout) is called for multiple times, it has to be idempotent.

Proposed Changes

1.  Add a forceClose flag to sender.
2. When forceClose flag is set, sender will not send any more messages but fail all the messages in RecordAccumulator and wake up the threads waiting on a callback. These threads may be doing:
   
   1. synchronized send
   2. flush()
3. Cleanup metrics and release other resources.

Compatibility, Deprecation, and Migration Plan

This is a backward compatible change.

Rejected Alternatives

None