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For (3), fetching of a topic's metadata is a blocking operation in the producer, which is all the more surprising because it blocks in a function that's advertised as asynchronous! . This means that a pipeline of records to be submitted for various uncached topics will serially block while fetching an individual topic's metadata.

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Impact on client will be strictly internal performance improvements; no public APIs, protocols, or other external factors are being changed.

Rejected Alternatives

If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other wayNone with serious consideration.