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https://issues.apache.org/jira/browse/KAFKA-9952?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jason Gustafson resolved KAFKA-9952.
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Fix Version/s: 2.6.0
Resolution: Fixed
> Reconsider immediate propagation of hw when replica selector is used
> --------------------------------------------------------------------
>
> Key: KAFKA-9952
> URL: https://issues.apache.org/jira/browse/KAFKA-9952
> Project: Kafka
> Issue Type: Improvement
> Reporter: Jason Gustafson
> Priority: Major
> Fix For: 2.6.0
>
>
> For KIP-392, we added logic to make sure that high watermark changes are
> propagated to followers without delay in order to improve end to end latency
> when fetching from followers. The downside of this change is that it
> increases the rate of fetch requests from followers which can have a
> noticeable impact on performance (see KAFKA-9731). To fix that problem, we
> modified the code so that we only propagate high watermark changes
> immediately when a replica selector is used (which is not the default).
> However, we should consider whether we want to go even further and disable
> immediate propagation of the high watermark more generally since it makes
> this feature risky to use. Instead, users can use the max wait time in order
> to control the worst-case latency. Note that this is typically only a problem
> for low-throughput topics since otherwise we will have a steady rate of high
> watermark updates.
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