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From "Jason Brown (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13700) Heartbeats can cause gossip information to go permanently missing on certain nodes
Date Thu, 20 Jul 2017 18:00:02 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16095090#comment-16095090
] 

Jason Brown commented on CASSANDRA-13700:
-----------------------------------------

re: CASSANDRA-11825. Yes, shared mutable state strikes again, and thanks for addressing them
separately ;)

> Heartbeats can cause gossip information to go permanently missing on certain nodes
> ----------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-13700
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13700
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Distributed Metadata
>            Reporter: Joel Knighton
>            Assignee: Joel Knighton
>            Priority: Critical
>
> In {{Gossiper.getStateForVersionBiggerThan}}, we add the {{HeartBeatState}} from the
corresponding {{EndpointState}} to the {{EndpointState}} to send. When we're getting state
for ourselves, this means that we add a reference to the local {{HeartBeatState}}. Then, once
we've built a message (in either the Syn or Ack handler), we send it through the {{MessagingService}}.
In the case that the {{MessagingService}} is sufficiently slow, the {{GossipTask}} may run
before serialization of the Syn or Ack. This means that when the {{GossipTask}} acquires the
gossip {{taskLock}}, it may increment the {{HeartBeatState}} version of the local node as
stored in the endpoint state map. Then, when we finally serialize the Syn or Ack, we'll follow
the reference to the {{HeartBeatState}} and serialize it with a higher version than we saw
when constructing the Ack or Ack2.
> Consider the case where we see {{HeartBeatState}} with version 4 when constructing an
Ack and send it through the {{MessagingService}}. Then, we add some piece of state with version
5 to our local {{EndpointState}}. If {{GossipTask}} runs and increases the {{HeartBeatState}}
version to 6 before the {{MessageOut}} containing the Ack is serialized, the node receiving
the Ack will believe it is current to version 6, despite the fact that it has never received
a message containing the {{ApplicationState}} tagged with version 5.
> I've reproduced in this in several versions; so far, I believe this is possible in all
versions.



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