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Status

Current state: Draft

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

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

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

Motivation

FindCoordinator only allows to look up the coordinator for a single resource at a time. For use cases working with several consumer groups for example, this forces to send many FindCoordinator requests and this can have a negative impact on performance.

This is evident in all all consumer groups methods of the Admin API:

• deleteConsumerGroups()
• describeConsumerGroups()
• listConsumerGroups()

These take a collection of groups as input. Being able to find coordinators in batches would allow to use a single find coordinator request to resolve them all instead of 1 request per group as of today.

Public Interfaces

We'll rename the FindCoordinator API to FindCoordinators

FindCoordinators API

Bump FindCoordinatorsRequest version to 4 and include a new field "CoordinatorKeys". The existing "Key" field will be limited to versions less than 4. As we don't have use cases for finding coordinators for both groups and transactions at the same time, the "KeyType" field is kept and specifies the request type for all keys in "CoordinatorKeys".

{
  "apiKey": 10,
  "type": "request",
  "name": "FindCoordinatorsRequest",
  // Version 1 adds KeyType.
  //
  // Version 2 is the same as version 1.
  //
  // Version 3 is the first flexible version.
  //
  // Version 4 adds CoordinatorKeys
  "validVersions": "0-4",
  "flexibleVersions": "3+",
  "fields": [
    { "name": "Key", "type": "string", "versions": "0-3",
      "about": "The coordinator key." },
    { "name": "KeyType", "type": "int8", "versions": "1+", "default": "0", "ignorable": false,
      "about": "The coordinator key type. (Group, transaction, etc.)" },
    { "name": "CoordinatorKeys", "type": "[]string", "versions": "4+",
      "about": "The coordinator keys." }
  ]
}

Bump FindCoordinatorsResponse version to 4 and include a new field "CoordinatorKeys".

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.