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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]

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

Motivation

in Tiered Storage, indexes are uploaded together with the segment log (on the same operation RemoteStorageManager#copyLogSegment ) when segments become available for uploading to remote tier. However, when consumer fetching hits remote data, each index is fetched individually and cached in-memory at the broker. Even though fetching segment indexes is an action that happens at least once per segment, the fact that each segment index is fetched independently can lead to an increased latency when fetching across segments. This can become a more pressing issue when the segment sizes are smaller than default (e.g. 10s of MBs).

Remote Storage Manager implementations (referred as plugins) can optimize how segment indexes are uploaded given that all indexes are uploaded on the same operation, and are immutable. 

For instance, plugins can choose to upload the segment indexes as part of the same object.

However, fetching segment indexes individually is more expensive given that remote fetch round-trip is comparatively the most expensive operation in terms of latency and carries a (usually small) cost.  

Public Interfaces

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

A public interface is any change to the following:

• Binary log format

• The network protocol and api behavior

• Any class in the public packages under clientsConfiguration, especially client configuration

  • org/apache/kafka/common/serialization

  • org/apache/kafka/common

  • org/apache/kafka/common/errors

  • org/apache/kafka/clients/producer

  • org/apache/kafka/clients/consumer (eventually, once stable)

• Monitoring

• Command line tools and arguments

• Anything else that will likely break existing users in some way when they upgrade

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?

Test Plan

Describe in few sentences how the KIP will be tested. We are mostly interested in system tests (since unit-tests are specific to implementation details). How will we know that the implementation works as expected? How will we know nothing broke?

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.