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Discussion thread: here , and here
JIRA: here [Change the link from KAFKA-1 to your own ticket] Jira server ASF JIRA serverId 5aa69414-a9e9-3523-82ec-879b028fb15b key KAFKA-15868
Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
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Performance was tested using the kafka-producer-perf-test.sh script and reassigning leadership of all partitions of a 100 partition topic. We see an end-to-end reduction in the p99.9 produce latency of the overall run of 88%, from 1675ms to 215ms (average of 3 runs). Digging deeper into the baseline, & rejected alternate, metadata RPC becomes slow due to slower produce RPCs ahead of it to a given broker. This results into metadata refresh being slow for baseline & rejected alternate over all, resulting into higher latencies. KIP-951 doesn't rely on the Metadata RPC for the new leader information, hence sees better latencies.
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