Status

Current state: Under DiscussionAccepted

Discussion thread: here

JIRA: KAFKA-5856

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The request can must be sent to any brokerthe controller.

The request will require the ALTER operation on the Topic resource.

The request is subject to the CreateTopicPolicy of the broker as configured by the broker's create.topic.policy.class.name config property. This is to ensure that the policy applies to topics modified after creation.

After validating the request the broker calls AdminUtils.addPartitions() which ultimately updates the topic partition assignment znode (/brokers/topics/${topic}).

The controller then waits for the change to the number of partitions to be reflected in its metadata cache before sending the CreatePartitionsResponse.

CreatePartitionsRequest => [topic_partition_count] timeout
  topic_partition_count => topic partition_count
    topic => STRING
    partition_count => count [assignment]
      count => INT32
      assignment => [INT32]
  timeout => INT32

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assignment

Note: When a NewPartitions is constructed without a newAssignments array it results in a null assignment array in the CreatePartitionsRequest.

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• TOPIC_AUTHORIZATION_FAILED (29) The user lacked Alter on the topic

• POLICY_VIOLATION(44) The request violated the configured policy

•  INVALID_TOPIC_EXCEPTION (17) If the topic doesn't exist

• INVALID_PARTITIONS (37) If the partition count was <= the current partition count for the topic.
• INVALID_REPLICA_ASSIGNMENT (39)  if the size of any of the lists contained in the partitions list was not equal to the topic replication factor.
• INVALID_REQUEST (42) If duplicate topics appeared in the request, or the size of the partitions list did not equal the number of new partitions, or if the size of any of the lists contained in the partitions list was not equal to the topic replication factor
• REASSIGNMENT_IN_PROGRESS (new) If a partition reassignment is in progress. It is necessary to prevent increasing partitions at the same time so that we can be sure the partition has a meaningful replication factor.
• NONE (0) The topic partition count was changed successfully.

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• NewPartitions could take an increment, rather than the new "absolute" number of partitions. But this makes the request non-idempotent, with consequent possibilities of a double increment. This would be particularly bad because it's not possible to decrease the partition count.
• NewPartitions could take a complete assignment for both old and new partitions. This would incorrectly suggest that the request could increase the number of partitions and effect a reassignment of the existing partitions at the same time. The server would have to either ignore the old partitions (in which case why were they required to be provided?) or validate them (in which case the client has to know the old assignment in order to add more, which is needlessly difficult).

Numerous names were considered: increasePartitions, increatePartitionCount, increaseNumPartitions, addPartitions. It was felt that createPartitions() successfully implied that only an increase was possible, and was consistent with createTopics. Simiarly numerous names were considered for NewPartitions. The name of the static factory methods was chosen to alleviate the awkward semantics mentioned above, making it clear that the number argument was the new total partition count, and not an increment.

Consideration was given to whether to support non-consecutive partition ids. No use cases for non-consecutive partition ids were identified, so this is not supported.