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https://issues.apache.org/jira/browse/YARN-5915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15678475#comment-15678475
]
Atul Sikaria edited comment on YARN-5915 at 11/19/16 3:13 AM:
--------------------------------------------------------------
This was seen previously as well, in YARN-4814.
The issue is with writeEntities method in FileSystemTimelineWriter
(https://github.com/apache/hadoop/blob/trunk/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/client/api/impl/FileSystemTimelineWriter.java#L317).
This calls getObjectMapper().writeValue(…), which does a flush() after every
write with default config.
{noformat}
@Override
public void writeValue(JsonGenerator jgen, Object value)
throws IOException, JsonGenerationException, JsonMappingException
{
SerializationConfig config = copySerializationConfig();
if (config.isEnabled(SerializationConfig.Feature.CLOSE_CLOSEABLE) && (value
instanceof Closeable)) {
_writeCloseableValue(jgen, value, config);
} else {
_serializerProvider.serializeValue(config, jgen, value,
_serializerFactory);
if
(config.isEnabled(SerializationConfig.Feature.FLUSH_AFTER_WRITE_VALUE)) {
jgen.flush();
}
}
}
{noformat}
On filesystems that map flush() to no-op or trivial operations, this is not a
big deal. But on filesystems where flush() incurs a larger cost, this becomes a
bottleneck for timeline events flow.
The fix is to set the property above (FLUSH_AFTER_WRITE_VALUE) to false, so the
JSonGenerator does not do a flush after every JSon write.
The flush of the stream is done in a timer thread at configurable interval (10
seconds by default). As [~jlowe] pointed out in YARN-4814, the timer thread
also needs to also do a flush() on the JsonGenerator, to make sure the json
serializer does not have any buffered data - so the hflush() in the timer
thread actually flushes all the data seen so far.
was (Author: asikaria):
This was seen previously as well, in YARN-4814.
The issue is with writeEntities method in FileSystemTimelineWriter
(https://github.com/apache/hadoop/blob/trunk/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/client/api/impl/FileSystemTimelineWriter.java#L317).
This calls getObjectMapper().writeValue(…), which does a flush() after every
write with default config.
{noformat}
@Override
public void writeValue(JsonGenerator jgen, Object value)
throws IOException, JsonGenerationException, JsonMappingException
{
SerializationConfig config = copySerializationConfig();
if (config.isEnabled(SerializationConfig.Feature.CLOSE_CLOSEABLE) && (value
instanceof Closeable)) {
_writeCloseableValue(jgen, value, config);
} else {
_serializerProvider.serializeValue(config, jgen, value,
_serializerFactory);
if
(config.isEnabled(SerializationConfig.Feature.FLUSH_AFTER_WRITE_VALUE)) {
jgen.flush();
}
}
}
{noformat}
On filesystems that map flush() to no-op or trivial operations, this is not a
big deal. But on filesystems where flush() incurs a larger cost, this becomes a
bottleneck for timeline events flow.
> ATS 1.5 FileSystemTimelineWriter causes flush() to be called after every
> event write
> ------------------------------------------------------------------------------------
>
> Key: YARN-5915
> URL: https://issues.apache.org/jira/browse/YARN-5915
> Project: Hadoop YARN
> Issue Type: Bug
> Components: timelineserver
> Affects Versions: 3.0.0-alpha1
> Reporter: Atul Sikaria
>
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