pnowojski commented on a change in pull request #11877:
URL: https://github.com/apache/flink/pull/11877#discussion_r665342075
##########
File path:
flink-runtime/src/main/java/org/apache/flink/runtime/io/network/partition/PipelinedSubpartition.java
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@@ -315,6 +326,17 @@ BufferAndBacklog pollBuffer() {
if (buffer.readableBytes() > 0) {
break;
}
+
+ // if we have an empty finished buffer and the exclusive
credit is 0, we just return
+ // the empty buffer so that the downstream task can release
the allocated credit for
+ // this empty buffer, this happens in two main scenarios
currently:
+ // 1. all data of a buffer builder has been read and after
that the buffer builder
+ // is finished
+ // 2. in approximate recovery mode, a partial record takes a
whole buffer builder
+ if (buffersPerChannel == 0 && bufferConsumer.isFinished()) {
+ break;
+ }
+
Review comment:
If there are two buffers, first is empty the second one can be:
1. non empty buffer
2. empty buffer
3. event
In all cases, instead of sending this first empty buffer with the backlog
information, as far as I understand, it should be possible to just send any of
the above instead with the updated backlog information. From the downstream
node perspective, it should make no difference if we hide this empty buffer. If
this is 2nd or 3rd case, we should be able to release the floating buffer
regardless of that, shouldn't we?
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