[jira] [Assigned] (ZOOKEEPER-4921) Zookeeper Client 3.9.3 Fails to Reconnect After Network Failures

["Kezhu Wang (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ZOOKEEPER-4921?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Kezhu Wang reassigned ZOOKEEPER-4921:
-------------------------------------

    Assignee: Kezhu Wang

> Zookeeper Client 3.9.3 Fails to Reconnect After Network Failures
> ----------------------------------------------------------------
>
>                 Key: ZOOKEEPER-4921
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-4921
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: java client
>    Affects Versions: 3.9.3
>            Reporter: Chuong Tran
>            Assignee: Kezhu Wang
>            Priority: Critical
>
> After upgrading the Java Zookeeper client to version 3.9.3, we observed that it is not resilient to brief network disruptions, such as a short VPN blip. In such cases, the client attempts to reconnect only once, and if unsuccessful, the session expires.
> {quote}Apr 23, 2025 10:19:23 AM com.twitter.finagle.common.zookeeper.ZooKeeperClient$3 process
> INFO: Zookeeper session expired. Event: WatchedEvent state:Expired type:None path:null zxid: -1
> {quote}
> In contrast, the previous version (3.9.2) would continuously retry until the network connection was restored, maintaining the session more reliably.
> I believe it's a new issue with this change: https://issues.apache.org/jira/browse/ZOOKEEPER-4508
>  
> Step to repro:
>  # Open VPN.
>  # Start the application which connects to the Zookeeper server with the VPN.
>  # Disable VPN for a couple of minutes.
>  # Observe the application.
>  # Enable the VPN again.
> {quote}3.9.3:
> "message" : "Session 0x0 for server XXX, Closing socket connection. Attempting reconnect except it is a SessionExpiredException or SessionTimeoutException.",
>   "stackTrace" : "o.a.z.ClientCnxn$SessionTimeoutException: Client session timed out, have not heard from server in 5590ms for session id 0x0
>         at o.a.z.ClientCnxn$SendThread.run(ClientCnxn.java:1253)
> {quote}
> 3.9.2: Application will be reconnected successfully.



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