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What's more, the metadata's fetch only need to be done one time in whole blocking of KafkaProducer#send. After the complete of first fetch, the metadata will be retrieved from cache directly and its timer update only happen on network thread.

So, this KIP try to reach the goal we can change the max.block.ms to wanted smaller value without worry worrying about the metadata's fetch. 

Public Interfaces

No public interface changed. Just change the inner implement of private method:

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