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The current default for `zookeeper.session.timeout.ms` is 6s. This may have been was reasonable for controlled local datacenter environments, but over time, Kafka has increasingly been deployed in more unstable cloud environments. More unstable conditions means more spurious timeouts which can have a bad impact on partition availability. Here we propose to increase the default to 18s.

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The default values changes in this KIP are listed in the table below.

Proposed Changes

As discussed above, we will increase the default zookeeper session timeout to 18s. The tradeoff with a larger session timeout is that it allows the system to smooth over transient instability at the cost of slower detection of genuine failures. Based on our experience, genuine failures are rare in proportion to the various events that can cause a node to temporarily lose connectivity to the zookeeper quorum.

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