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We will introduce a message chunking approach to reduce overall memory consumption during down-conversion. The idea is to lazily and incrementally down-convert messages message "chunks" in a batched fashion, and send the result out to the consumer as soon as the chunk is ready. The broker continuously down-converts chunks of messages and sends them out, until it has exhausted all messages contained in the FetchResponse, or has reached some predetermined threshold. This way, we use a small, deterministic amount of memory per FetchResponse.
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