zhijiangW commented on a change in pull request #6417: [FLINK-9913][runtime]
Improve output serialization only once in RecordWriter
URL: https://github.com/apache/flink/pull/6417#discussion_r213343581
##########
File path:
flink-runtime/src/main/java/org/apache/flink/runtime/io/network/api/writer/RecordWriter.java
##########
@@ -87,62 +86,71 @@ public RecordWriter(ResultPartitionWriter writer,
ChannelSelector<T> channelSele
this.numChannels = writer.getNumberOfSubpartitions();
- /*
- * The runtime exposes a channel abstraction for the produced
results
- * (see {@link ChannelSelector}). Every channel has an
independent
- * serializer.
- */
- this.serializers = new SpanningRecordSerializer[numChannels];
+ this.serializer = new SpanningRecordSerializer<T>();
this.bufferBuilders = new Optional[numChannels];
for (int i = 0; i < numChannels; i++) {
- serializers[i] = new SpanningRecordSerializer<T>();
bufferBuilders[i] = Optional.empty();
}
}
public void emit(T record) throws IOException, InterruptedException {
+ serializer.serializeRecord(record);
+
for (int targetChannel : channelSelector.selectChannels(record,
numChannels)) {
- sendToTarget(record, targetChannel);
+ copyToTarget(targetChannel);
}
+
+ // Make sure we don't hold onto the large intermediate
serialization buffer for too long
+ serializer.prune();
}
/**
* This is used to broadcast Streaming Watermarks in-band with records.
This ignores
* the {@link ChannelSelector}.
*/
public void broadcastEmit(T record) throws IOException,
InterruptedException {
+ serializer.serializeRecord(record);
+
for (int targetChannel = 0; targetChannel < numChannels;
targetChannel++) {
- sendToTarget(record, targetChannel);
+ copyToTarget(targetChannel);
}
+
+ serializer.prune();
}
/**
* This is used to send LatencyMarks to a random target channel.
*/
public void randomEmit(T record) throws IOException,
InterruptedException {
- sendToTarget(record, rng.nextInt(numChannels));
- }
+ serializer.serializeRecord(record);
- private void sendToTarget(T record, int targetChannel) throws
IOException, InterruptedException {
- RecordSerializer<T> serializer = serializers[targetChannel];
+ copyToTarget(rng.nextInt(numChannels));
- SerializationResult result = serializer.addRecord(record);
+ serializer.prune();
+ }
+ private void copyToTarget(int targetChannel) throws IOException,
InterruptedException {
+ // We should reset the initial position of the intermediate
serialization buffer before
+ // copying, so the serialization results can be copied to
multiple target buffers.
+ serializer.reset();
+
+ BufferBuilder bufferBuilder = getBufferBuilder(targetChannel);
+ SerializationResult result =
serializer.copyToBufferBuilder(bufferBuilder);
while (result.isFullBuffer()) {
- if (tryFinishCurrentBufferBuilder(targetChannel,
serializer)) {
- // If this was a full record, we are done. Not
breaking
- // out of the loop at this point will lead to
another
- // buffer request before breaking out (that
would not be
- // a problem per se, but it can lead to stalls
in the
- // pipeline).
- if (result.isFullRecord()) {
- break;
- }
+ tryFinishCurrentBufferBuilder(targetChannel);
Review comment:
You pointed out a good question!
1. Considering `tryFinishCurrentBufferBuilder()`, the logic is somewhat
different from before. In the past, the buffer builder may be empty when
calling `tryFinishCurrentBufferBuilder()`, then it returns a boolean value to
indicate the result. But now, we know the buffer builder is always present when
calling `tryFinishCurrentBufferBuilder`, so we may change it to
`finishCurrentBufferBuilder()` seems more appropriate. And adds the check code
instead as following:
```
private void finishCurrentBufferBuilder(int targetChannel) {
checkState(bufferBuilders[targetChannel].isPresent());
BufferBuilder bufferBuilder =
bufferBuilders[targetChannel].get();
bufferBuilders[targetChannel] = Optional.empty();
numBytesOut.inc(bufferBuilder.finish());
}
```
2. But I think we still need call `finishCurrentBufferBuilder()` after
checking every full buffer. Because in the while loop the serialized record may
be copied into several different buffer builders, and each buffer build
referenced by the `bufferBuilders ` needs to be finished when full.
3. It actually seems better than before, as the loop exit not rely on the
return value of `tryFinishCurrentBufferBuilder()`.
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