Status

Current state: Under Discussion

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

JIRA: KAFKA-7206 [Change the link from KAFKA-1 to your own ticket]

Motivation

Today each FindCoordinatorRequest only contains a single consumer id at a time. That means if we have N number of groupIds that need to find it's coordinators, we would have to send out N number of requests. This is not as efficient in some scenarios. Therefore we want to extend FindCoordinatorRequest to have multiple consumer ids.

Proposed Changes

Send a single FindCoordinatorRequest to a broker asking for coordinators of all consumer groups. These are the changes that need to be make:

1. Update the Schema in FindCoordinatorRequest to store an array of groupID (with a new FIND_COORDINATOR_REQUEST_V3); modify the class structure to take more than one coordinatorKey (List<String> groupIds). 
2. Update FindCoordinatorResponse 's class to have a mapping structure (now it only has Node to support one result, we need to support multiple results so something like <GroupId, CoordinatorNodeMetadata>)
3. Update handleFindCoordinatorRequest to correctly parse the new FindCoordinatorRequest and map the result to the new FindCoordinatorResponse.

Public Interfaces

API Changes

I suggest that we modify FindCoordinatorRequest.java to support multiple coordinator key by adding a new FIND_COORDINATOR_REQUEST_V3:

public class FindCoordinatorRequest extends AbstractRequest {
    private static final String COORDINATOR_KEY_KEY_NAME = "coordinator_key";
    private static final String COORDINATOR_TYPE_KEY_NAME = "coordinator_type";
	private static final String COORDINATOR_GROUPIDS_KEY_NAME = "coordinator_groupIds"


	private static final Schema FIND_COORDINATOR_REQUEST_V0 = new Schema(GROUP_ID);

	private static final Schema FIND_COORDINATOR_REQUEST_V1 = new Schema(
        new Field("coordinator_key", STRING, "Id to use for finding the coordinator (for groups, this is the groupId, " +
                        "for transactional producers, this is the transactional id)"),
        new Field("coordinator_type", INT8, "The type of coordinator to find (0 = group, 1 = transaction)"));


	/**
 	* The version number is bumped to indicate that on quota violation brokers send out responses before throttling.
 	*/
	private static final Schema FIND_COORDINATOR_REQUEST_V2 = FIND_COORDINATOR_REQUEST_V1;


	private static final Schema FIND_COORDINATOR_REQUEST_V3 = new Schema(
	new Field(COORDINATOR_GROUPIDS_KEY_NAME, new ArrayOf(DESCRIBE_GROUPS_RESPONSE_MEMBER_V0), "All the coordinator ids " +
        "for this request"));

	...


	private final Map<String, String> groupIds; // Use to store <coordinator_key, coordinator_type> pair

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.