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https://issues.apache.org/jira/browse/FLINK-9913?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16605751#comment-16605751
]
ASF GitHub Bot commented on FLINK-9913:
---------------------------------------
pnowojski 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_r215615035
##########
File path:
flink-runtime/src/main/java/org/apache/flink/runtime/io/network/api/writer/RecordWriter.java
##########
@@ -89,77 +88,101 @@ 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];
+ this.broadcastChannels = new int[numChannels];
for (int i = 0; i < numChannels; i++) {
- serializers[i] = new SpanningRecordSerializer<T>();
+ broadcastChannels[i] = i;
bufferBuilders[i] = Optional.empty();
}
}
public void emit(T record) throws IOException, InterruptedException {
- for (int targetChannel : channelSelector.selectChannels(record,
numChannels)) {
- sendToTarget(record, targetChannel);
- }
+ emitToTargetChannels(record,
channelSelector.selectChannels(record, numChannels));
}
/**
* This is used to broadcast Streaming Watermarks in-band with records.
This ignores
* the {@link ChannelSelector}.
*/
public void broadcastEmit(T record) throws IOException,
InterruptedException {
- for (int targetChannel = 0; targetChannel < numChannels;
targetChannel++) {
- sendToTarget(record, targetChannel);
- }
+ emitToTargetChannels(record, broadcastChannels);
}
/**
* 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);
+
+ if (copyToTargetBuffers(rng.nextInt(numChannels))) {
+ serializer.prune();
+ }
}
- private void sendToTarget(T record, int targetChannel) throws
IOException, InterruptedException {
- RecordSerializer<T> serializer = serializers[targetChannel];
+ private void emitToTargetChannels(T record, int[] targetChannels)
throws IOException, InterruptedException {
+ serializer.serializeRecord(record);
+
+ boolean pruneAfterCopying = false;
+ for (int channel : targetChannels) {
+ if (copyToTargetBuffers(channel)) {
+ pruneAfterCopying = true;
+ }
+ }
- SerializationResult result = serializer.addRecord(record);
+ // Make sure we don't hold onto the large intermediate
serialization buffer for too long
+ if (pruneAfterCopying) {
+ serializer.prune();
+ }
+ }
+ /**
+ * Copies the intermediate serialization buffer to the BufferBuilder of
the target channel, also
+ * checks to prune the intermediate buffer iif the target BufferBuilder
is fulfilled and the record
+ * is full.
+ *
+ * @param targetChannel the target channel to get BufferBuilder
+ * @return <tt>true</tt> if the intermediate serialization buffer
should be pruned
+ */
+ private boolean copyToTargetBuffers(int targetChannel) throws
IOException, InterruptedException {
Review comment:
Third time I'm looking at this PR and third time I had to think for a minute
what does the this method. I'm always forgetting that `serializer` is a class
field and that this method copies from it.
Maybe rename to `copyFromSerializerToTargetChannel`? Imo rename would allow
us to drop most of the java doc and simplify it to just:
```
/**
* @param targetChannel
* @return <tt>true</tt> if the intermediate serialization buffer
should be pruned
*/
```
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> Improve output serialization only once in RecordWriter
> ------------------------------------------------------
>
> Key: FLINK-9913
> URL: https://issues.apache.org/jira/browse/FLINK-9913
> Project: Flink
> Issue Type: Improvement
> Components: Network
> Affects Versions: 1.6.0
> Reporter: zhijiang
> Assignee: zhijiang
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.7.0
>
>
> Currently the {{RecordWriter}} emits output into multi channels via
> {{ChannelSelector}} or broadcasts output to all channels directly. Each
> channel has a separate {{RecordSerializer}} for serializing outputs, that
> means the output will be serialized as many times as the number of selected
> channels.
> As we know, data serialization is a high cost operation, so we can get good
> benefits by improving the serialization only once.
> I would suggest the following changes for realizing it.
> # Only one {{RecordSerializer}} is created in {{RecordWriter}} for all the
> channels.
> # The output is serialized into the intermediate data buffer only once for
> different channels.
> # The intermediate serialization results are copied into different
> {{BufferBuilder}}s for different channels.
> An additional benefit by using a single serializer for all channels is that
> we get a potentially significant reduction on heap space overhead from fewer
> intermediate serialization buffers (only once we got over 5MiB, these buffers
> were pruned back to 128B!).
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