Github user tzulitai commented on a diff in the pull request:
https://github.com/apache/flink/pull/3314#discussion_r102668004
--- Diff:
flink-connectors/flink-connector-kafka-0.8/src/main/java/org/apache/flink/streaming/connectors/kafka/internals/SimpleConsumerThread.java
---
@@ -373,16 +370,28 @@ else if (partitionsRemoved) {
keyPayload.get(keyBytes);
}
- final T value =
deserializer.deserialize(keyBytes, valueBytes,
-
currentPartition.getTopic(), currentPartition.getPartition(), offset);
-
- if
(deserializer.isEndOfStream(value)) {
- // remove
partition from subscribed partitions.
-
partitionsIterator.remove();
- continue
partitionsLoop;
- }
-
- owner.emitRecord(value,
currentPartition, offset);
+ final Collector<T>
collector = new Collector<T>() {
--- End diff --
What I think we should do to solve this correctly:
Buffer the elements collected from the `deserialize` call. The
`Collector.collect` implementation should simply add the collected element to
the buffer, and not emit it immediately.
After `deserialize` returns, call `emitRecord` once with all the elements
in the buffer and the original record's offset. This, of course, would mean we
need to slightly change the `emitRecord` implementation a bit to something like:
```
void emitRecord(List<T> records, KafkaTopicPartitionState<KPH>
partitionState, long offset) {
synchronized (checkpointLock) {
for (T record : records) {
sourceContext.collect(record);
}
partitionState.setOffset(offset);
}
}
```
After this, we proceed with the next record and repeat. Note that the
emitting of all produced elements from record at offset 100L and the update to
the offset state to 100L happens atomically synchronized on the checkpoint
lock, so we can make sure that a checkpoint barrier will only come either
after or before all the produced records of offset 100, and not in-between.
I think we should also be able to avoid a per-record `Collector` with this
solution. We can reuse a `Collector` and provide it to the `deserializer` for
every record, because it's simply only a means to collect elements to the
internal buffer and we're not calling `emitRecords` in it.
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