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From "Jonathan Ellis (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-1391) Allow Concurrent Schema Migrations
Date Mon, 14 Nov 2011 17:33:51 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13149767#comment-13149767
] 

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

bq. As all of the migrations are user initiated we can easily calculate what modifications
migration makes and propagate only them 

Yes, that's implied by moving to a CF-based structure I think.

bq. keeping TimeUUID as ID of the migration to identify "apply" order

I don't see why you'd want to complicate things by doing this.  We already have perfectly
good per-column conflict resolution without it.

bq. it would be very useful to have the logic abstracted from schemas so it can be used for
other use cases

I'm okay in principle with introducing a EveryNodeReplicationStrategy but refactoring migrations
to that is a separate step from this ticket.
                
> 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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