curcur commented on a change in pull request #13501:
URL: https://github.com/apache/flink/pull/13501#discussion_r498890005
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File path:
flink-runtime/src/main/java/org/apache/flink/runtime/io/network/buffer/BufferBuilder.java
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@@ -86,11 +94,34 @@ public int append(ByteBuffer source) {
int available = getMaxCapacity() - positionMarker.getCached();
int toCopy = Math.min(needed, available);
+ // Each Data BufferBuilder starts with a 4-byte integer header
+ // Since length can only be 0 or positive numbers, the first
bit of the integer
+ // is used to identify whether the first record is partial (1)
or not (0)
+ // The remaining 31 bits stands for the length of the record
remaining.
+ // The data written is not made visible to reader until {@link
#commit()}, so the BufferBuilder
+ // ends either with a complete record or full buffer after
append();
+ if (isEmptyBufferBuilder()) {
+ available = available - BUFFER_BUILDER_HEADER_SIZE;
+ toCopy = Math.min(needed, available);
+ int header =
Header.headerEncode(isPartialRecord(source), toCopy);
+
memorySegment.putIntBigEndian(positionMarker.getCached(), header);
+ positionMarker.move(BUFFER_BUILDER_HEADER_SIZE);
+ }
+
Review comment:
1. `ByteBuffer source` contains the header length of a record, we use
that length to decide where a record ends;
`Partial record` needs to address the problem that if a record spanning over
multiple buffers and the first buffer is sent but lost due to failure. They are
trying to address different problems.
2. The second question is more complicated. I will write my concerns a bit
later, together with Stephan's question.
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