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From "Jonathan Ellis (Commented) (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-1391) Allow Concurrent Schema Migrations
Date Thu, 05 Jan 2012 17:38:40 GMT


Jonathan Ellis commented on CASSANDRA-1391:

bq. Instead of converting deserialized thrift objects to KSMetaData we would need to initialize
KSMetaData/CFMetaData and populate those with parameters from db, is it really better?

At the least, it lets you re-use apply/diff instead of rewriting that, and easy CASSANDRA-2477.

bq. With current patch user will be able to do "SELECT * FROM system.keyspaces" and other
queries but after CASSANDRA-2474 is done because `system.keyspaces` uses composite columns

Does it?  It sure looks like it uses serialized Thrift objects to me.  (Looking at DefsTable.loadFromStorage.)
> 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
>             Fix For: 1.1
>         Attachments: 0001-new-migration-schema-and-avro-methods-cleanup.patch, 0002-avro-removal.patch,
0003-oldVersion-removed-new-migration-distribution-schema.patch, 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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