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https://issues.apache.org/jira/browse/FLINK-9913?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16576424#comment-16576424
 ] 

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_r209284512
 
 

 ##########
 File path: 
flink-runtime/src/main/java/org/apache/flink/runtime/io/network/api/writer/RecordWriter.java
 ##########
 @@ -188,24 +192,32 @@ public void setMetricGroup(TaskIOMetricGroup metrics) {
 
        /**
         * Marks the current {@link BufferBuilder} as finished and clears the 
state for next one.
-        *
-        * @return true if some data were written
         */
-       private boolean tryFinishCurrentBufferBuilder(int targetChannel, 
RecordSerializer<T> serializer) {
-
-               if (!bufferBuilders[targetChannel].isPresent()) {
-                       return false;
+       private void tryFinishCurrentBufferBuilder(int targetChannel) {
+               if (bufferBuilders[targetChannel].isPresent()) {
+                       BufferBuilder bufferBuilder = 
bufferBuilders[targetChannel].get();
+                       bufferBuilders[targetChannel] = Optional.empty();
+                       numBytesOut.inc(bufferBuilder.finish());
                }
-               BufferBuilder bufferBuilder = 
bufferBuilders[targetChannel].get();
-               bufferBuilders[targetChannel] = Optional.empty();
+       }
 
-               numBytesOut.inc(bufferBuilder.finish());
-               serializer.clear();
-               return true;
+       /**
+        * The {@link BufferBuilder} may already exist if not filled up last 
time, otherwise we need
+        * request a new one for this target channel.
+        */
+       @Nonnull
 
 Review comment:
   Imo you don't have to add `@Nonnull` annotation. I'm implicitly assuming 
that any non `@Nullable` marked field is automatically `@Nonnull`.

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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: Minor
>              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.



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