[jira] [Created] (CASSANDRA-14930) decommission may cause timeout because messaging backlog is cleared

["ZhaoYang (JIRA)" <ji...@apache.org>]

ZhaoYang created CASSANDRA-14930:
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             Summary: decommission may cause timeout because messaging backlog is cleared 
                 Key: CASSANDRA-14930
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-14930
             Project: Cassandra
          Issue Type: Bug
          Components: Coordination, Core
            Reporter: ZhaoYang
            Assignee: ZhaoYang
             Fix For: 3.0.x, 3.11.x


On a 3-node cluster with RF=2, decommissioning a node may cause quorum write timeout because messaging backlog to decommissioned node is cleared via {{Gossiper#removeEndpoint() -> OutboundTcpConnection#closeSocket()}}.
(Timeout is less likely to happen with RF=3, because we can afford one less response)

{code:java}
What happened:
1. [WriteStage] before the leaving node is removed from tokenmetadata, the write endpoints are generated ( leaving endpoint is included )
2. [GossipStage] the leaving node is removed from tokenmetadata, no more future write handler will include leaving endpoints
3. [WriteStage] write handlers sends messages to messaging-service backlog
4. [GossipStage] messaging-service backlog is cleared, messages are not sent and connection closed
5. [WriteStage] write time out
 {code}


| patch |
| [3.0|https://github.com/jasonstack/cassandra/commits/decommission_timeout_3.0]  |
| [3.0|https://github.com/jasonstack/cassandra/commits/decommission_timeout_3.11]  |

We can avoid it by delaying to destroy messaging connection so that messages are sent and responded. New messaging framework rewrite in {{Trunk}} avoids the issues by not clearing messaging backlog.




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