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Stefan Podkowinski commented on CASSANDRA-13569:
------------------------------------------------
The main point of the patch was to prevent runnables from pilling up in
{{maybeScheduleSchemaPull}} as scheduled by:
{{ScheduledExecutors.nonPeriodicTasks.schedule(runnable, MIGRATION_DELAY_IN_MS,
TimeUnit.MILLISECONDS);}}
Your patch is undoing this change and is instead now preventing concurrent
execution per endpoint of MigrationTask. But keep in mind here that
MigrationTask itself is short lived and non-blocking. Using your suggested
approach would not be very effective to throttle migration requests and would
probably not help a lot for preventing the problem stated in the first
paragraph.
> 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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