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https://issues.apache.org/jira/browse/SOLR-12087?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16408948#comment-16408948
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Cao Manh Dat commented on SOLR-12087:
-------------------------------------

Hi Varun, all your points are valid. Thanks!

Several points from the log you are mentioned are worth to concern
 * Multiple log {{ZkShardTerms failed to save terms, version is not a match, 
retrying}}, this is a ZK performance problem, all thread will try to fetch the 
latest term from ZK -> SOLR-12135
 * DistributedUpdateProcessor Core core_node4 belonging to 
deleteReplicaOnIndexing shard1, does not have error'd node -> SOLR-12073

 

> Deleting replicas sometimes fails and causes the replicas to exist in the 
> down state
> ------------------------------------------------------------------------------------
>
>                 Key: SOLR-12087
>                 URL: https://issues.apache.org/jira/browse/SOLR-12087
>             Project: Solr
>          Issue Type: Bug
>      Security Level: Public(Default Security Level. Issues are Public) 
>          Components: SolrCloud
>    Affects Versions: 7.2
>            Reporter: Jerry Bao
>            Priority: Critical
>         Attachments: SOLR-12087.patch, SOLR-12087.test.patch, Screen Shot 
> 2018-03-16 at 11.50.32 AM.png
>
>
> Sometimes when deleting replicas, the replica fails to be removed from the 
> cluster state. This occurs especially when deleting replicas en mass; the 
> resulting cause is that the data is deleted but the replicas aren't removed 
> from the cluster state. Attempting to delete the downed replicas causes 
> failures because the core does not exist anymore.
> This also occurs when trying to move replicas, since that move is an add and 
> delete.
> Some more information regarding this issue; when the MOVEREPLICA command is 
> issued, the new replica is created successfully but the replica to be deleted 
> fails to be removed from state.json (the core is deleted though) and we see 
> two logs spammed.
>  # The node containing the leader replica continually (read every second) 
> attempts to initiate recovery on the replica and fails to do so because the 
> core does not exist. As a result it continually publishes a down state for 
> the replica to zookeeper.
>  # The deleted replica node spams that it cannot locate the core because it's 
> been deleted.
> During this period of time, we see an increase in ZK network connectivity 
> overall, until the replica is finally deleted (spamming DELETEREPLICA on the 
> shard until its removed from the state)
> My guess is there's two issues at hand here:
>  # The leader continually attempts to recover a downed replica that is 
> unrecoverable because the core does not exist.
>  # The replica to be deleted is having trouble being deleted from state.json 
> in ZK.
> This is mostly consistent for my use case. I'm running 7.2.1 with 66 nodes.



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