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From "Pavel Yaskevich (Updated) (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-1391) Allow Concurrent Schema Migrations
Date Tue, 17 Jan 2012 16:27:41 GMT


Pavel Yaskevich updated CASSANDRA-1391:

    Attachment: CASSANDRA-1391.patch

Migrations are made one-time local thing, serialization/deserialization and save to system
cfs are removed. Schema is propagated in from of row mutations to be applied on the system
'keyspaces' cf (apply/diff strategy), upon local user-initiated migration node uses push tactic
(sends updated schema state to all alive nodes in the cluster), pull tactic (when node requests
schema from remote node) is enabled only when node detects schema disagreement by means of
Gossip e.g. when new node joins the ring or push was lost due to network or other circumstances.
Supports automatic schema migration from old storage (after migration deprecated system 'schema'
and 'migrations' column families are dropped). toAvro() methods are removed as no longer needed,
fromAvro(...) methods are kept as @Deprecated to support schema migration from schema cf to
new cf. 'Keyspaces' CF contain data in the human-readable JSON format.
> 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: 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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