Kafka shuts down abnormally and restarts, always taking more than a few hours to load

[wenbing shen]

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             Kafka shuts down abnormally and restarts, always taking more
            than a few hours to load.
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            We used Kafka-2.0.0,we tried to turn it
            up num.recovery.threads.per.data.dir,but the startup
process is always
            limited by the slow loading of partitions.We observed a
partition that took
            two hours to load.
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            The action of the partition in the startup process is mainly
            Loading producer state from snapshot file and writing
producer snapshotat
            offset.
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            A lot of time is spent in rebuildProducerState and
            segment.recover methods.
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            The cluster consists of 21 nodes, each with about 1500
            partitions and 700 partition leaders.
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            Is there any way to reduce the startup time of Kafka when it
            shuts down abnormally?