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https://issues.apache.org/jira/browse/CASSANDRA-1391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13171781#comment-13171781
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Jonathan Ellis commented on CASSANDRA-1391:
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Feels more like a simplification, than a complication to me. Syncing schema
becomes always sending exactly one message instead of potentially
hundreds/thousands. And, we get full concurrency support instead of "mostly"
(the equal-timestamp weakness I mentioned). Seems worth it to me.
Currently, schema changes are push-only (see: SS.pushMigrations). So without
changing that, yes, both nodes will send schema to each other (which will be a
no-op on the newer one). That's not a blocker for me. I'd be fine switching
to a pull model in either this or a followup ticket, which would let the newer
side skip its pull if it recognizes the remote version as one it used to have
(which would reliably indicate it's "older" even if timestamp ties are
involved).
Traffic from schema changes will be negligible for any known workload. We can
optimize for that if/when it becomes a problem (my prediction: never).
> 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:
> 0001-new-migration-schema-and-avro-methods-cleanup.patch,
> 0002-avro-removal.patch, 0003-oldVersion-removed-nit-fixed.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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