[improve][io] JDBC sink: replace synchronized queue with LinkedBlockingDeque for proper back-pressure#17
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…ngDeque for proper back-pressure Replaces manual `synchronized(incomingList)` blocks with JDK's `LinkedBlockingDeque` for proper blocking back-pressure instead of the nack/redeliver storm caused by `record.fail()`. Key changes: - Use `offer(record, 1s timeout)` in write() to block the Pulsar IO thread when queue is full, stopping message consumption naturally - Use `drainTo()` in flush() for non-blocking atomic batch drain - Replace recursive flush() with iterative while loop - Move isFlushing.set(false) to finally block - Drain remaining records in close() for clean shutdown Follows the established pattern used by Aerospike, HDFS, Kinesis, and DynamoDB connectors in this repository. Fixes apache#16
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Motivation
Follow-up to #9. The
record.fail()back-pressure introduced in #9 causes a nack/redeliver storm under sustained load — the consumer delivers messages, the sink immediately fails them, they get redelivered, repeating endlessly. This wastes CP time.Modifications
Replace
LinkedList+synchronizedwithLinkedBlockingDeque:write():offer(record, 1, TimeUnit.SECONDS)blocks the Pulsar IO thread when queue is full — this IS the back-pressure (stops consumption). At most 1 nack/second on timeout vs. thousands/second before.flush():drainTo(swapList, batchSize)— non-blocking atomic drain, no synchronized blocks. Automatically wakes blockedoffer()calls by making space.flush()uses awhileloop instead of recursive self-calls.isFlushinginfinally: prevents stuck flag after exceptions.close()drains queue: fails remaining records for clean shutdown.Follows the pattern already used by Aerospike (
LinkedBlockingDeque), HDFS, Kinesis, and DynamoDB (LinkedBlockingQueue) connectors in this repo.Verifying this change
testBoundedQueueBackPressuremay need timeout adjustment (6th write now blocks 1s instead of failing instantly)Fixes #16