Source:
public RecordAppendResult append(TopicPartition tp, long timestamp, byte[] key, byte[] value, Header[] headers, Callback callback, long maxTimeToBlock, boolean abortOnNewBatch, long nowMs) throws InterruptedException { appendsInProgress.incrementAndGet(); ByteBuffer buffer = null; if (headers == null) headers = Record.EMPTY_HEADERS; try { Deque<ProducerBatch> dq = getOrCreateDeque(tp); synchronized (dq) { if (closed) throw new KafkaException("Producer closed while send in progress"); RecordAppendResult appendResult = tryAppend(timestamp, key, value, headers, callback, dq, nowMs); if (appendResult != null) return appendResult; } if (abortOnNewBatch) { return new RecordAppendResult(null, false, false, true); } byte maxUsableMagic = apiVersions.maxUsableProduceMagic(); int size = Math.max(this.batchSize, AbstractRecords.estimateSizeInBytesUpperBound(maxUsableMagic, compression, key, value, headers)); log.trace("Allocating a new byte message buffer for topic partition {}", size, tp.topic(), tp.partition()); buffer = free.allocate(size, maxTimeToBlock); synchronized (dq) { if (closed) throw new KafkaException("Producer closed while send in progress"); RecordAppendResult appendResult = tryAppend(timestamp, key, value, headers, callback, dq, nowMs); if (appendResult != null) { return appendResult; } MemoryRecordsBuilder recordsBuilder = recordsBuilder(buffer, maxUsableMagic); ProducerBatch batch = new ProducerBatch(tp, recordsBuilder, nowMs); FutureRecordMetadata future = Objects.requireNonNull(batch.tryAppend(timestamp, key, value, headers, callback, nowMs)); dq.addLast(batch); incomplete.add(batch); buffer = null; return new RecordAppendResult(future, dq.size() > 1 || batch.isFull(), true, false); } } finally { if (buffer != null) free.deallocate(buffer); appendsInProgress.decrementAndGet(); } }

Target:
public RecordAppendResult append(TopicPartition tp, long timestamp, byte[] key, byte[] value, Header[] headers, Callback callback, long maxTimeToBlock, boolean abortOnNewBatch, long nowMs) throws InterruptedException { appendsInProgress.incrementAndGet(); ByteBuffer buffer = null; if (headers == null) headers = Record.EMPTY_HEADERS; try { Deque<ProducerBatch> dq = getOrCreateDeque(tp); synchronized (dq) { if (closed) throw new KafkaException("Producer closed while send in progress"); RecordAppendResult appendResult = tryAppend(timestamp, key, value, headers, callback, dq, nowMs); if (appendResult != null) return appendResult; } if (abortOnNewBatch) { return new RecordAppendResult(null, false, false, true); } byte maxUsableMagic = apiVersions.maxUsableProduceMagic(); int size = Math.max(this.batchSize, AbstractRecords.estimateSizeInBytesUpperBound(maxUsableMagic, compression, key, value, headers)); log.trace("Allocating a new byte message buffer for topic partition {}", size, tp.topic(), tp.partition()); buffer = free.allocate(size, maxTimeToBlock); nowMs = time.milliseconds(); synchronized (dq) { if (closed) throw new KafkaException("Producer closed while send in progress"); RecordAppendResult appendResult = tryAppend(timestamp, key, value, headers, callback, dq, nowMs); if (appendResult != null) { return appendResult; } MemoryRecordsBuilder recordsBuilder = recordsBuilder(buffer, maxUsableMagic); ProducerBatch batch = new ProducerBatch(tp, recordsBuilder, nowMs); FutureRecordMetadata future = Objects.requireNonNull(batch.tryAppend(timestamp, key, value, headers, callback, nowMs)); dq.addLast(batch); incomplete.add(batch); buffer = null; return new RecordAppendResult(future, dq.size() > 1 || batch.isFull(), true, false); } } finally { if (buffer != null) free.deallocate(buffer); appendsInProgress.decrementAndGet(); } }