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https://issues.apache.org/jira/browse/FLINK-22643?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17565043#comment-17565043
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Piotr Nowojski edited comment on FLINK-22643 at 7/11/22 2:52 PM:
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After closing a ticket I forgot to mention that this seemed to have improved
low latency performance of the network stack by quite a bit
!Screenshot 2022-07-11 at 16.49.42.png|width=1000!
Previously the difference between 100ms and 1ms in the microbenchmark was ~18%,
after merging this change it's around ~4%.
was (Author: pnowojski):
After closing a ticket I forgot to mention that this seemed to have improved
low latency performance of the network stack by quite a bit !Screenshot
2022-07-11 at 16.49.42.png|width=650! Previously the difference between 100ms
and 1ms in the microbenchmark was ~18%, after merging this change it's around
~4%.
> Too many TCP connections among TaskManagers for large scale jobs
> ----------------------------------------------------------------
>
> Key: FLINK-22643
> URL: https://issues.apache.org/jira/browse/FLINK-22643
> Project: Flink
> Issue Type: Improvement
> Components: Runtime / Network
> Affects Versions: 1.14.0, 1.13.2
> Reporter: Zhilong Hong
> Assignee: fanrui
> Priority: Minor
> Labels: auto-deprioritized-major, pull-request-available
> Fix For: 1.15.0
>
> Attachments: Screenshot 2022-07-11 at 16.49.42.png
>
>
> For the large scale jobs, there will be too many TCP connections among
> TaskManagers. Let's take an example.
> For a streaming job with 20 JobVertices, each JobVertex has 500 parallelism.
> We divide the vertices into 5 slot sharing groups. Each TaskManager has 5
> slots. Thus there will be 400 taskmanagers in this job. Let's assume that job
> runs on a cluster with 20 machines.
> If all the job edges are all-to-all edges, there will be 19 * 20 * 399 * 2 =
> 303,240 TCP connections for each machine. If we run several jobs on this
> cluster, the TCP connections may exceed the maximum limit of linux, which is
> 1,048,576. This will stop the TaskManagers from creating new TCP connections
> and cause task failovers.
> As we run our production jobs on a K8S cluster, the job always failover due
> to exceptions related to network, such as {{Sending the partition request to
> 'null' failed}}, and etc.
> We think that we can decrease the number of connections by letting tasks
> reuse the same connection. We implemented a POC that makes all tasks on the
> same TaskManager reuse one TCP connection. For the example job we mentioned
> above, the number of connections will decrease from 303,240 to 15960. With
> the POC, the frequency of meeting exceptions related to network in our
> production jobs drops significantly.
> The POC is illustrated in:
> https://github.com/wsry/flink/commit/bf1c09e80450f40d018a1d1d4fe3dfd2de777fdc
>
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