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https://issues.apache.org/jira/browse/FLINK-21201?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17278069#comment-17278069
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Piotr Nowojski commented on FLINK-21201:
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I think this is a valid point. I've changed this to improvement as I don't
think this is a bug, it's behaving exactly the way it was designed to do but
with some limitations :)
I haven't given this much thought, but maybe instead of delegating to the
IOExecutor, we could just move the construction (or initialisation) of the
result partitions to the Task's thread? Or maybe we could make the creation of
the files (loop inside
{{ResultPartitionFactory#initializeBoundedBlockingPartitions}} lazy somehow?
I guess I would be more in favour of the first approach, moving all heavy
operations to the Task thread?
> Creating BoundedBlockingSubpartition blocks TaskManager’s main thread
> ---------------------------------------------------------------------
>
> Key: FLINK-21201
> URL: https://issues.apache.org/jira/browse/FLINK-21201
> Project: Flink
> Issue Type: Improvement
> Components: Runtime / Network
> Affects Versions: 1.12.1
> Reporter: Zhilong Hong
> Priority: Major
> Attachments: jobmanager.log.tar.gz, taskmanager.log.tar.gz
>
>
> When we are trying to run batch jobs with 8k parallelism, it takes a long
> time to deploy the vertices. After the investigation, we find that creating
> BoundedBlockingSubpartition blocks TaskManager’s main thread during the
> procedure of {{submitTask}}.
> When JobMaster invokes {{submitTask}} and sends an RPC call to the
> TaskManager, the TaskManager will receive the RPC call and execute the
> {{submitTask}} method in its main thread. In the {{submitTask}} method, the
> TaskExecutor will create a Task instance and try to start it. During the
> creation, the TaskExecutor will create the ResultPartition and its
> ResultSubpartitions.
> For the batch job, the type of ResultSubpartitions is the
> BoundedBlockingSubpartition with the FileChannelBoundedData. The
> BoundedBlockingSubpartition will create a file on the local disk, which is an
> IO operation and could take a long time.
> In our test, it would take at most 30+ seconds to create 8k
> BoundedBlockingSubpartitions. This procedure blocks the main thread of the
> TaskManager, and would lead to heartbeat timeout and slow task deploying. In
> my opinion, the IO operation should be executed with IOExecutor rather than
> the main thread.
> I add several log items to show what TaskExecutor is doing during
> {{submitTask}}.
> {code:java}
> 2021-01-29 14:44:37,557 INFO
> org.apache.flink.runtime.taskexecutor.TaskExecutor [] - Start to
> submit task #898 (c9aefd1d30c2b133ba04ad495cd894fd)
> 2021-01-29 14:44:37,557 INFO
> org.apache.flink.runtime.taskexecutor.slot.TaskSlotTableImpl [] - Activate
> slot 38cafd5b456cc8ff873bbe18e4bf708a.
> 2021-01-29 14:44:37,932 INFO
> org.apache.flink.runtime.taskexecutor.TaskExecutor [] - Start to
> init Task #898 (c9aefd1d30c2b133ba04ad495cd894fd) instance.
> 2021-01-29 14:44:37,932 INFO
> org.apache.flink.runtime.io.network.NettyShuffleEnvironment [] - Start to
> create 1 result partition(s).
> 2021-01-29 14:44:37,932 INFO
> org.apache.flink.runtime.io.network.partition.ResultPartitionFactory [] -
> Initializing BoundedBlockingResultPartitions
> 2021-01-29 14:44:37,932 INFO
> org.apache.flink.runtime.io.network.partition.ResultPartitionFactory [] -
> Start to create 8000 FILE BoundedBlockingSubpartitions.
> 2021-01-29 14:44:37,932 INFO
> org.apache.flink.runtime.io.network.partition.BoundedBlockingSubpartition []
> - FileChannel #0 created.
> ... ...
> 2021-01-29 14:45:06,052 INFO
> org.apache.flink.runtime.io.network.partition.BoundedBlockingSubpartition []
> - FileChannel #7999 created.
> 2021-01-29 14:45:06,052 INFO
> org.apache.flink.runtime.io.network.partition.ResultPartitionFactory [] -
> Finish creating 8000 FILE BoundedBlockingSubpartitions.
> 2021-01-29 14:45:06,052 INFO
> org.apache.flink.runtime.io.network.NettyShuffleEnvironment [] - Finish
> creating 1 result partition(s).
> 2021-01-29 14:45:06,052 INFO
> org.apache.flink.runtime.taskexecutor.TaskExecutor [] - Finish
> initializing task #898 (c9aefd1d30c2b133ba04ad495cd894fd) instance.
> 2021-01-29 14:45:06,052 INFO
> org.apache.flink.runtime.taskexecutor.TaskExecutor [] - Received
> task Source: Source 0 (898/8000)#0 (c9aefd1d30c2b133ba04ad495cd894fd), deploy
> into slot with allocation id 38cafd5b456cc8ff873bbe18e4bf708a.
> 2021-01-29 14:45:06,053 INFO org.apache.flink.runtime.taskmanager.Task
> [] - Source: Source 0 (898/8000)#0
> (c9aefd1d30c2b133ba04ad495cd894fd) switched from CREATED to DEPLOYING.
> {code}
> We can see that it takes nearly 29 seconds to create 8k
> BoundedBlockingSubpartitions, and this would blocks the main thread in the
> TaskExecutor.
> The log of JobManager and TaskManager is attached below. The most typical
> task is Source 0: #898.
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