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Status

Current state: [One of "Under Discussion", "Accepted", "Rejected"]Adopted (2.2.0)

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

JIRA: NAhere [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

Describe the problems you are trying to solve.

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

When fixing the issue in 

Jira
server ASF JIRA serverId 5aa69414-a9e9-3523-82ec-879b028fb15b key KAFKA-7652

 regarding the wrong old values being flushed to downstream, I realized the root cause was that we are trying to fetch the exact session's key with the provided key, start-time, end-time, but since there's no single-fetch API we are mimicking it with a range buggy query. On the other hand, like WindowStore, if users know which session they are querying exactly, they should be able to issue a "single-point" query, which should be much less costly as well compared to a range query. Such API could also help fixing the immediate issue of KAFKA-7652 as well.

Public Interfaces

This KIP would propose to add a single fetch API to the SessionStore interface:

Code Block
language java
AGG fetchSession(K key, long startTime, long endTime);

Internally, this function will be used in 1) caching store flush listener, to read the old value from underlying store; 2) for accessing values from the session store in storeGetter.

Proposed Changes

As above.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

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• Users implementing customized session-store would now need to make code changes to add one more function implementation for the added API. The reason that we've decided to not have an default implementation (e.g. have a very conservative range query, and use a condition to filter out all but only leave one that has the exact start/end timestamp) in the public API is that this one is going to be used inside the library as well at critical code paths, e.g. caching store's flush logic. And hence we really need this API implementation to be efficient.

Rejected Alternatives

1. I've considered adding this API to ReadOnlySessionStore, but realized it is not a very useful API for interactive queries since most IQ users would not know the exact session start-end timestamps.