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https://issues.apache.org/jira/browse/FLINK-9913?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16605753#comment-16605753
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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_r215611369
##########
File path:
flink-runtime/src/main/java/org/apache/flink/runtime/io/network/api/writer/RecordWriter.java
##########
@@ -197,40 +214,39 @@ public void setMetricGroup(TaskIOMetricGroup metrics) {
* Marks the current {@link BufferBuilder} as finished and clears the
state for next one.
*/
private void tryFinishCurrentBufferBuilder(int targetChannel) {
- if (bufferBuilders[targetChannel].isPresent()) {
- BufferBuilder bufferBuilder =
bufferBuilders[targetChannel].get();
+ Optional<BufferBuilder> bufferBuilderOpt =
bufferBuilders[targetChannel];
Review comment:
Rename to `bufferBuilder` (marking type in variable name is not the best
practice).
Have you seen throughput improvements by introducing this local variable? If
not, maybe revert the change?
FYI: When I was writing this code, I didn't see any performance improvement
(and I was testing this exact change). Removing one extra CPU cache read
(second `bufferBuilders[targetChannel]` access will either be optimised out or
it will be a read from CPU caches/registries) usually hardly matters compared
to taking locks :(
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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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