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https://issues.apache.org/jira/browse/IMPALA-7496?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tim Armstrong updated IMPALA-7496:
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Target Version: Product Backlog
> Schedule query taking in account the mem available on the impalad nodes
> -----------------------------------------------------------------------
>
> Key: IMPALA-7496
> URL: https://issues.apache.org/jira/browse/IMPALA-7496
> Project: IMPALA
> Issue Type: New Feature
> Components: Backend
> Reporter: Adriano
> Priority: Major
> Labels: admission-control, scheduler
>
> Environment description: cluster scale (50/100/150 nodes and terabyte of ram
> available) - Admission Control enabled.
> Issue description:
> Despite the coordinator chosen (with data and statistics unchanged) a query
> will be planned always in the same way based on the metainfo that the
> coordinator have.
> The query will be scheduled always on the same nodes if the memory
> requirements for the admission are satisfied:
> https://github.com/cloudera/Impala/blob/cdh5-2.7.0_5.9.1/be/src/scheduling/admission-controller.cc#L307-L333
> Equal queries are planned/scheduled always in the same way (to hit always the
> same nodes).
> This often lead to queue the queries that are hitting the same nodes are
> queued (not admitted) as on those nodes there's no more memory available
> within its process limit despite the pool have lot of free memory and the
> overall cluster load is low.
> When the plan is finished and the query can be evaluated to be admitted often
> happen that the admission is denied because one of the node have not enough
> memory to run the query operation (and the query is moved in the pool queue)
> despite the cluster have 50/100/150 nodes and terabyte of ram available.
> Why the scheduler does not take in consideration the memory available on the
> nodes involved in the query before to buid the schedule, (maybe preferring a
> remote read/operation on a free memory node instead to include in the plan
> always the same nodes that will end to be:
> 1- overloaded
> 2- the query will be not immediately admitted, risking to be timedout in the
> pool queue
> Since 2.7 the REPLICA_PREFERENCE can possibly help, but it's not good enough
> as it does not prevent the scheduler to choose busy nodes (with the same
> potential effect: query queued for lack of resource on specific node despite
> there are terabytes of free memory).
> Feature Request:
> It would be good if Impala had an option to execute queries (even with worse
> performance) excluding the nodes overloaded and including different nodes in
> order to get the query immediately admitted and executed.
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