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https://issues.apache.org/jira/browse/FLINK-16030?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17036108#comment-17036108
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Piotr Nowojski commented on FLINK-16030:
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Currently our threading model and network stack can not reliably support
heartbeats on data network channels (we do have them on akka). The reason is
that we are performing blocking operations inside Netty threads (we were
recently discussing [this
here|http://mail-archives.apache.org/mod_mbox/flink-dev/202002.mbox/browser]).
Unless the keep alive is set to value like 1 hour, I would be afraid that If we
add such feature, we will get more false positive connection timeouts,
confusing users and causing us more new problems than solving old ones.
> Add heartbeat between netty server and client to detect long connection alive
> -----------------------------------------------------------------------------
>
> Key: FLINK-16030
> URL: https://issues.apache.org/jira/browse/FLINK-16030
> Project: Flink
> Issue Type: Improvement
> Components: Runtime / Network
> Reporter: begginghard
> Priority: Major
>
> Network can fail in many ways, sometimes pretty subtle (e.g. high ratio
> packet loss).
> When the long tcp connection between netty client and server is lost, the
> server would failed to send response to the client, then shut down the
> channel. At the same time, the netty client does not know that the connection
> has been disconnected, so it has been waiting for two hours.
> To detect the long tcp connection alive on netty client and server, we should
> have two ways: tcp keepalive and heartbeat.
>
> The tcp keepalive is 2 hours by default. When the long tcp connection dead,
> you continue to wait for 2 hours, the netty client will trigger exception and
> enter failover recovery.
> If you want to detect quickly, netty provides IdleStateHandler which it use
> ping-pang mechanism. If netty client sends continuously n ping message and
> receives no one pang message, then trigger exception.
>
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