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https://issues.apache.org/jira/browse/FLINK-25417?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17463763#comment-17463763
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Zhilong Hong commented on FLINK-25417:
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I think maybe it's duplicated with FLINK-22643.
> Too many connections for TM
> ---------------------------
>
> Key: FLINK-25417
> URL: https://issues.apache.org/jira/browse/FLINK-25417
> Project: Flink
> Issue Type: Improvement
> Components: Runtime / Network
> Affects Versions: 1.15.0, 1.13.5, 1.14.2
> Reporter: fanrui
> Priority: Major
> Attachments: image-2021-12-22-19-17-59-486.png,
> image-2021-12-22-19-18-23-138.png
>
>
> Hi masters, when the number of task exceeds 10, some TM has more than 4000
> TCP connections.
> !image-2021-12-22-19-17-59-486.png|width=1388,height=307!
>
> h2. Reason:
> When the task is initialized, the downstream InputChannel will connect to the
> upstream ResultPartition.
> In PartitionRequestClientFactory#createPartitionRequestClient, there is a
> clients({_}ConcurrentMap<ConnectionID,
> CompletableFuture{_}{_}<NettyPartitionRequestClient>{_}{_}> clients{_}). It's
> a cache to avoid repeated tcp connections. But the ConnectionID has a field
> is connectionIndex.
> The connectionIndex comes from IntermediateResult, which is a random number.
> When multiple Tasks are running in a TM, other TMs need to establish multiple
> connections to this TM, and each Task has a NettyPartitionRequestClient.
> Assume that the parallelism of the flink job is 100, each TM has 20 Tasks,
> and the Partition strategy between tasks is rebalance or hash. Then the
> number of connections for a single TM is (20-1) * 100 * 2 = 3800. If multiple
> such TMs are running on a single node, there is a risk.
>
> I want to know whether it is risky to change the cache key to
> connectionID.address? That is: a tcp connection is shared between all Tasks
> of TM.
> I guess it is feasible because:
> # I have tested it and the task can run normally.
> # The Message contains the InputChannelID, which is used to distinguish
> which channel the NettyMessage belongs to.
>
> !image-2021-12-22-19-18-23-138.png|width=2953,height=686!
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