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From "Shalin Shekhar Mangar (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-11932) ZkCmdExecutor: Retry ZkOperation on SessionExpired
Date Mon, 05 Feb 2018 17:41:00 GMT

    [ https://issues.apache.org/jira/browse/SOLR-11932?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16352678#comment-16352678
] 

Shalin Shekhar Mangar commented on SOLR-11932:
----------------------------------------------

ZkCmdExecutor cannot work on session expiry because the command sent to the ZkCmdExecutor
has an instance of SolrZooKeeper instance is no longer usable after expiry. A new SolrZooKeeper
instance must be created after session expiry. The right way to handle session expiry is to
use the OnReconnect hook in ZkController.addOnReconnectListener and re-initialize state as
needed.

> ZkCmdExecutor: Retry ZkOperation on SessionExpired 
> ---------------------------------------------------
>
>                 Key: SOLR-11932
>                 URL: https://issues.apache.org/jira/browse/SOLR-11932
>             Project: Solr
>          Issue Type: Bug
>      Security Level: Public(Default Security Level. Issues are Public) 
>    Affects Versions: 7.2
>            Reporter: John Gallagher
>            Assignee: Ishan Chattopadhyaya
>            Priority: Major
>         Attachments: SessionExpiredLog.txt, zk_retry.patch
>
>
> We are seeing situations where an operation, such as changing a replica's state to active
after a recovery, fails because the zk session has expired.
> However, these operations seem like they are retryable, because the ZookeeperConnect
receives an event that the session expired and tries to reconnect.
> That makes the SessionExpired handling scenario seem very similar to the ConnectionLoss
handling scenario, so the ZkCmdExecutor seems like it could handle them in the same way.
>  
> Here's an example stack trace with some slight redactions: [^SessionExpiredLog.txt] 
In this case, a zk operation (a read) failed with a SessionExpired event, which seems retriable. 
The exception kicked off a reconnection, but seems like the subsequent operation, (publishing
as active) failed (perhaps it was using a stale connection handle at that point?)
>  
> Regardless, the watch mechanism that reestablishes connection on SessionExpired seems
sufficient to allow the ZkCmdExecutor to retry that operation at a later time and have hope
of succeeding.
>  
> I have included a simple patch we are trying that catches both exceptions instead of
just ConnectionLossException: [^zk_retry.patch]



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