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https://issues.apache.org/jira/browse/FLINK-31144?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17691416#comment-17691416
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Weihua Hu commented on FLINK-31144:
-----------------------------------
Thanks for reporting this issue. [~jto]
DefaultPreferredLocationsRetriever.getPreferredLocationsBasedOnInputs will go
over all the input locations which may cost much time when the topology is
complex. Maybe make PreferredLocations configurable is an option to solve this
problem.
I have some more questions about this issue:
1. Is the slow scheduling or the sheduled result of lolcation preferred make
your job slow?
2. "we have complex jobs where this issue can cause batch "pause" of 40+
minutes" What does "pause" meaning? Is the
getPreferredLocationsBasedOnInputs take more than 40+ minutes? Could you
provide the topology of the complex job.
> Slow scheduling on large-scale batch jobs
> ------------------------------------------
>
> Key: FLINK-31144
> URL: https://issues.apache.org/jira/browse/FLINK-31144
> Project: Flink
> Issue Type: Bug
> Components: Runtime / Coordination
> Reporter: Julien Tournay
> Priority: Major
> Attachments: flink-1.17-snapshot-1676473798013.nps
>
>
> When executing a complex job graph at high parallelism
> `DefaultPreferredLocationsRetriever.getPreferredLocationsBasedOnInputs` can
> get slow and cause long pauses where the JobManager becomes unresponsive and
> all the taskmanagers just wait. I've attached a VisualVM snapshot to
> illustrate the problem.[^flink-1.17-snapshot-1676473798013.nps]
> At Spotify we have complex jobs where this issue can cause batch "pause" of
> 40+ minutes and make the overall execution 30% slower or more.
> More importantly this prevent us from running said jobs on larger cluster as
> adding resources to the cluster worsen the issue.
> We have successfully tested a modified Flink version where
> `DefaultPreferredLocationsRetriever.getPreferredLocationsBasedOnInputs` was
> completely commented and simply returns an empty collection and confirmed it
> solves the issue.
> In the same spirit as a recent change
> ([https://github.com/apache/flink/blob/43f419d0eccba86ecc8040fa6f521148f1e358ff/flink-runtime/src/main/java/org/apache/flink/runtime/scheduler/DefaultPreferredLocationsRetriever.java#L98-L102)]
> there could be a mechanism in place to detect when Flink run into this
> specific issue and just skip the call to `getInputLocationFutures`
> [https://github.com/apache/flink/blob/43f419d0eccba86ecc8040fa6f521148f1e358ff/flink-runtime/src/main/java/org/apache/flink/runtime/scheduler/DefaultPreferredLocationsRetriever.java#L105-L108.]
> I'm not familiar enough with the internals of Flink to propose a more
> advanced fix, however it seems like a configurable threshold on the number of
> consumer vertices above which the preferred location is not computed would
> do. If this solution is good enough, I'd be happy to submit a PR.
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