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From "Jonathan Ellis (Updated) (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-1391) Allow Concurrent Schema Migrations
Date Thu, 19 Jan 2012 23:46:40 GMT


Jonathan Ellis updated CASSANDRA-1391:

    Attachment: 1391-rebased.txt

rebased patch attached.  comments:

- validateSchemaAgreement is unnecessary now right?
- the old Migration infrastructure feels unnecessarily heavyweight now.  Can we move the validation
into the CassandraServer methods, and then just invoke a MigrationHelper method from a runnable
- should we snapshot the old avro schema before nuking it?
- SystemTable.dropOldSchemaTables is a no-op.  I think we can take this out entirely since
loadSchema/fromAvro takes care of it?
- Can you add a comment describing the layout of the new schema CFs to defstable or systemtable?
- I'd prefer to leave the low level slicing / deserialize in SystemTable class instead of
scattered between Schema and DefsTable
> Allow Concurrent Schema Migrations
> ----------------------------------
>                 Key: CASSANDRA-1391
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 0.7.0
>            Reporter: Stu Hood
>            Assignee: Pavel Yaskevich
>            Priority: Critical
>             Fix For: 1.1
>         Attachments: 1391-rebased.txt, 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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