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https://issues.apache.org/jira/browse/CASSANDRA-1391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12904304#action_12904304
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Jonathan Ellis commented on CASSANDRA-1391:
-------------------------------------------

ISTM we can allow concurrent migrations by computing the schema ID as an md5 of 
the keyspaces and CFs, instead of pushing that to VC.  it's exactly the kind of 
set-merge problem that both columns-within-a-CF and VC can handle.

> Allow Concurrent Schema Migrations
> ----------------------------------
>
>                 Key: CASSANDRA-1391
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1391
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Stu Hood
>
> CASSANDRA-1292 fixed multiple migrations started from the same node to 
> properly queue themselves, but it is still possible for migrations initiated 
> on different nodes to conflict and leave the cluster in a bad state. Since 
> the system_add/drop/rename methods are accessible directly from the client 
> API, they should be completely safe for concurrent use.
> It should be possible to allow for most types of concurrent migrations by 
> converting the UUID schema ID into a VersionVectorClock (as provided by 
> CASSANDRA-580).

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