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From "Ian Cleasby (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-14779) Changing EndpointSnitch via JMX has problems
Date Fri, 30 Nov 2018 01:55:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-14779?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16704052#comment-16704052
] 

Ian Cleasby edited comment on CASSANDRA-14779 at 11/30/18 1:54 AM:
-------------------------------------------------------------------

Added an exception to handle the case that JMX tries to update the Snitch which is going to
effectively change the topology.

Patch here:
[trunk|https://github.com/apache/cassandra/compare/trunk...PenguinRage:Changing-EndpointSnitch-via-JMX-has-problems]


was (Author: icleasby):
Added an exception to handle the case that JMX tries to update the Snitch which is going to
effectively change the topology.
[trunk|https://github.com/apache/cassandra/compare/trunk...PenguinRage:Changing-EndpointSnitch-via-JMX-has-problems]

> Changing EndpointSnitch via JMX has problems
> --------------------------------------------
>
>                 Key: CASSANDRA-14779
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-14779
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Distributed Metadata
>            Reporter: Benedict
>            Priority: Minor
>             Fix For: 4.x
>
>
> The snitch can be set via StorageService over JMX, for what reason I’m unsure. If this
were to happen, we might encounter the following problems:
>  * If the effective local DC were to change, we would not update it. Perhaps changing
the local DC of a node should be rejected and cause it to fail, but presently, it would simply
result in our disagreeing with the snitch.
>  * During the transition, routing of queries might be broken, as we fetch the snitch
multiple times in different locations when deciding where to route our query and writes. It’s
not clear what the outcome of a discordant view of the ring would be.
> Probably, changing this information in a live cluster is dangerous and we should actually
reject any effective changes to rack, or DC for any node. But presently we don’t seem to
corroborate that this information remains the same. We don’t seem to perform any cluster
wide confirmation that this data is consistent, generally, which perhaps we should also consider.



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