What is Kafka's RecordAccumulator and how does it buffer messages?

The RecordAccumulator is the producer-side in-memory buffer that queues records into batches before they are sent. It keeps a deque of ProducerBatch objects per topic-partition, and incoming records are appended to the current batch of their partition. A batch is ready to send when it is full (batch.size) or linger.ms has elapsed, or in a few other cases such as flush() or an exhausted buffer; the background Sender thread then drains the ready batches for each leader broker and sends them in ProduceRequests. Memory is bounded by buffer.memory (default 32 MB): when it is exhausted, send() blocks for up to max.block.ms, after which the producer returns a failed future with BufferExhaustedException (a subclass of TimeoutException). The producer metric buffer-available-bytes shows how much buffer memory is unused, which helps to spot buffer pressure.

Expected key concepts: RecordAccumulator, buffer, ProducerBatch, topic-partition, batch.size, linger.ms, Sender thread, buffer.memory, max.block.ms, BufferExhaustedException