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Date: Mon, 14 Nov 2011 21:14:54 +0000 (UTC)
From: "Jonathan Ellis (Commented) (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
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Subject: [jira] [Commented] (CASSANDRA-1391) Allow Concurrent Schema
 Migrations
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    [ https://issues.apache.org/jira/browse/CASSANDRA-1391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13149925#comment-13149925 ] 

Jonathan Ellis commented on CASSANDRA-1391:
-------------------------------------------

I'm enthusiastic about this approach for several reasons:

- ultimately we end up with simpler code with less special cases, although the migration (*cough*) from Avro-based schema will be a pain initially
- gets rid of Avro dependency!
- fixes CASSANDRA-2477 ("SELECT * FROM keyspaces")

                
> Allow Concurrent Schema Migrations
> ----------------------------------
>
>                 Key: CASSANDRA-1391
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1391
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 0.7.0
>            Reporter: Stu Hood
>            Assignee: Pavel Yaskevich
>             Fix For: 1.1
>
>         Attachments: CASSANDRA-1391.patch
>
>
> 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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