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https://issues.apache.org/jira/browse/CASSANDRA-1391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13096031#comment-13096031
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Gary Dusbabek commented on CASSANDRA-1391:
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bq. Merge algorithm is based on isolated schema initialized from merging
migration lastVersion point: merging migration applied first then all older
migrations, after that Schema.instance gets safely updated.
Could you clarify what you mean by "merging migration applied first, then all
older migrations..."?
It seems like a side effect of applying a migration is that it can apply other
migrations. Does MigrationManager.applyMigrations() need to be updated because
of this?
What does "isolated" indicate?
Try to put things like flushSystemTables() in a separate patch (ok on the same
ticket) to make reviewing the actual changes easier.
Would it be possible to create some unit tests for CFMD.diff()?
> 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
> Assignee: Pavel Yaskevich
> Fix For: 1.0
>
> 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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