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From "Stefan Podkowinski (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13569) Schedule schema pulls just once per endpoint
Date Wed, 28 Jun 2017 14:22:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16066564#comment-16066564
] 

Stefan Podkowinski commented on CASSANDRA-13569:
------------------------------------------------

The mentioned future for the delayed schema migration will only represent the status of the
scheduled execution, but not if the schema pull itself was successful. A completed future
simply indicates that the delayed execution took place. Afterwards we're free to try the next
schema pull if we have to. 

The intention of this ticket is not to redesign any retry/timeout semantics or to reimplement
the schema exchange protocol. This would need more careful thinking and should possibly done
in context of  CASSANDRA-10699.

> Schedule schema pulls just once per endpoint
> --------------------------------------------
>
>                 Key: CASSANDRA-13569
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13569
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Distributed Metadata
>            Reporter: Stefan Podkowinski
>            Assignee: Stefan Podkowinski
>             Fix For: 3.0.x, 3.11.x, 4.x
>
>
> Schema mismatches detected through gossip will get resolved by calling {{MigrationManager.maybeScheduleSchemaPull}}.
This method may decide to schedule execution of {{MigrationTask}}, but only after using a
{{MIGRATION_DELAY_IN_MS = 60000}} delay (for reasons unclear to me). Meanwhile, as long as
the migration task hasn't been executed, we'll continue to have schema mismatches reported
by gossip and will have corresponding {{maybeScheduleSchemaPull}} calls, which will schedule
further tasks with the mentioned delay. Some local testing shows that dozens of tasks for
the same endpoint will eventually be executed and causing the same, stormy behavior for this
very endpoints.
> My proposal would be to simply not schedule new tasks for the same endpoint, in case
we still have pending tasks waiting for execution after {{MIGRATION_DELAY_IN_MS}}.



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