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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-14779) Changing EndpointSnitch via JMX has problems
Date Fri, 02 Nov 2018 10:07:00 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-14779?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Benedict updated CASSANDRA-14779:
---------------------------------
    Description: 
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.

  was:
The snitch can be set via StorageProxy 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.



> 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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