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Status

Current state: [One of "Under Discussion", "Accepted", "Rejected"]

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

Storage is one of the key resources in a Kafka cluster. Administrators typically monitor the disk usage of each log directory via metrics to enable them to properly manage the storage attached to brokers. In order to build advanced tooling and automation, it would be useful to also be able to retrieve that information directly via the Kafka API. That would allow to easily validate whether disk operations (like a resize), or topic deletion (log deletion only happen after a short delay) have completed.

Public Interfaces

To expose logdirs total and usable space, this KIP proposes adding 2 new fields to the DescribeLogDirsResponse message and bumping its protocol version. The LogDirDescription class will also be updated to expose these 2 new fields to the Admin API.

Proposed Changes

DescribeLogDirs v4

No changes in the Request. Two new fields are added to the Response: TotalSpace and UsableSpace

{
  "apiKey": 35,
  "type": "response",
  "name": "DescribeLogDirsResponse",
  // Starting in version 1, on quota violation, brokers send out responses before throttling.
  "validVersions": "0-4",
  // Version 2 is the first flexible version.
  // Version 3 adds the top-level ErrorCode field
  // Version 4 adds the TotalSpace and UsableSpace fields
  "flexibleVersions": "2+",
  "fields": [
    { "name": "ThrottleTimeMs", "type": "int32", "versions": "0+",
      "about": "The duration in milliseconds for which the request was throttled due to a quota violation, or zero if the request did not violate any quota." },
    { "name": "ErrorCode", "type": "int16", "versions": "3+", "about": "The error code, or 0 if there was no error." },
    { "name": "Results", "type": "[]DescribeLogDirsResult", "versions": "0+",
      "about": "The log directories.", "fields": [
      { "name": "ErrorCode", "type": "int16", "versions": "0+",
        "about": "The error code, or 0 if there was no error." },
      { "name": "LogDir", "type": "string", "versions": "0+",
        "about": "The absolute log directory path." },
      { "name": "Topics", "type": "[]DescribeLogDirsTopic", "versions": "0+",
        "about": "Each topic.", "fields": [
          ...
        ]}
      ]},
      { "name": "TotalSpace", "type": "int64", "versions": "4+", "ignorable": true, "default": "-1",
        "about": "The total size of the log directory."
      },
      { "name": "UsableSpace", "type": "int64", "versions": "4+", "ignorable": true, "default": "-1",
        "about": "The usable size of the log directory."
      }
    ]}
  ]
}

LogDirDescription

Two new methods are added as well as a new constant:

public static final long UNKNOWN_SPACE = -1L;


public long totalSpace() { return totalSpace; }

public long usableSpace() { return usableSpace; }

When calling describeLogDirs() on a broker that does not support this feature, totalSpace() and usableSpace() will return UNKNOWN_SPACE.

ReplicaManager

When handling a DescribeLogDirs request, ReplicaManager will retrieve the totalSpace and usableSpace from each logdir.

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.