Stanislav Lukyanov created IGNITE-10808:
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             Summary: Discovery message queue may build up with 
TcpDiscoveryMetricsUpdateMessage
                 Key: IGNITE-10808
                 URL: https://issues.apache.org/jira/browse/IGNITE-10808
             Project: Ignite
          Issue Type: Bug
            Reporter: Stanislav Lukyanov
         Attachments: IgniteMetricsOverflowTest.java

A node receives a new metrics update message every `metricsUpdateFrequency` 
milliseconds, and the message will be put at the top of the queue (because it 
is a high priority message).
If processing one message takes more than `metricsUpdateFrequency` then 
multiple `TcpDiscoveryMetricsUpdateMessage` will be in the queue. A long enough 
delay (e.g. caused by a network glitch or GC) may lead to the queue building up 
tens of metrics update messages which are essentially useless to be processed. 
Finally, if processing a message on average takes a little more than 
`metricsUpdateFrequency` (even for a relatively short period of time, say, for 
a minute due to network issues) then the message worker will end up processing 
only the metrics updates and the cluster will essentially hang.

Reproducer is attached. In the test, the queue first builds up and then very 
slowly being teared down, causing "Failed to wait for PME" messages.

Need to change ServerImpl's SocketReader not to put another metrics update 
message to the top of the queue if it already has one (or replace the one on 
the top with new one).



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