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From "Aleksey Yeschenko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13569) Schedule schema pulls just once per endpoint
Date Fri, 16 Jun 2017 16:36:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16052106#comment-16052106
] 

Aleksey Yeschenko commented on CASSANDRA-13569:
-----------------------------------------------

After having a more thorough look (sorry for my quick incorrect initial suggestion), I'm still
bothered by the way the patch handles cleanup of the in-flight schedule tasks.

I made a minor alteration to use computeIfAbsent for scheduling and put clean up logic into
the scheduling Runnable. The rest of the patch is just factoring a method out. Haven't tested
any of it - my last day of vacation, running short on time.

I won't be able to complete the review if you oppose the suggestions, though, as I'm off to
a 3-week no-Cassandra vacation. Feel free to swap a reviewer in that case (:

> 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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