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Al M commented on SPARK-24474: ------------------------------ My initial tests suggest that this stops the issue from happening. Thanks! I will perform more tests to make 100% sure that it does not still occur. I am surprised that this config makes a difference. My tasks are usually quite big; normally taking about a minute each. I would not have expected a change from waiting 3s per task to 0s per task to make such a huge difference. Do you know if there is any unusual behaviour around this config setting? > Cores are left idle when there are a lot of tasks to run > -------------------------------------------------------- > > Key: SPARK-24474 > URL: https://issues.apache.org/jira/browse/SPARK-24474 > Project: Spark > Issue Type: Bug > Components: Scheduler > Affects Versions: 2.2.0 > Reporter: Al M > Priority: Major > > I've observed an issue happening consistently when: > * A job contains a join of two datasets > * One dataset is much larger than the other > * Both datasets require some processing before they are joined > What I have observed is: > * 2 stages are initially active to run processing on the two datasets > ** These stages are run in parallel > ** One stage has significantly more tasks than the other (e.g. one has 30k > tasks and the other has 2k tasks) > ** Spark allocates a similar (though not exactly equal) number of cores to > each stage > * First stage completes (for the smaller dataset) > ** Now there is only one stage running > ** It still has many tasks left (usually > 20k tasks) > ** Around half the cores are idle (e.g. Total Cores = 200, active tasks = > 103) > ** This continues until the second stage completes > * Second stage completes, and third begins (the stage that actually joins > the data) > ** This stage works fine, no cores are idle (e.g. Total Cores = 200, active > tasks = 200) > Other interesting things about this: > * It seems that when we have multiple stages active, and one of them > finishes, it does not actually release any cores to existing stages > * Once all active stages are done, we release all cores to new stages > * I can't reproduce this locally on my machine, only on a cluster with YARN > enabled > * It happens when dynamic allocation is enabled, and when it is disabled > * The stage that hangs (referred to as "Second stage" above) has a lower > 'Stage Id' than the first one that completes > * This happens with spark.shuffle.service.enabled set to true and false -- This message was sent by Atlassian JIRA (v7.6.3#76005) --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@spark.apache.org For additional commands, e-mail: issues-h...@spark.apache.org