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how spark distributes partitions to executors and how to distribute evenly

Explorer

I'm facing a severe performance issue on a job that suddenly(no code changes) takes 4x time to complete, after debugging and investigating I found most of the data is read to a single executor(13 GB one executor vs 200 MB the rest). Initially i thought it was an classical uneven partitions issue so i started to test different partition numbers (and criteria) but the issue was not fixed, I did a rows per partition analysis and found all partitions have similar number of rows so this is not the problem, it seems the scheduler assigns most partitions to a single executor instead of evenly, question is how spark decides which partitions go to which executor, and how to control that behavior to make distribution even? 

I asked this on SO too: https://stackoverflow.com/questions/67133177/how-spark-distributes-partitions-to-executors

2 REPLIES 2

Expert Contributor

Hello

 

Sounds like a Spark data skew problem

 

Some good approaches to consider

1. Broadcast join

2. Key Salting

 

You can make a reference here: https://itnext.io/handling-data-skew-in-apache-spark-9f56343e58e8

Explorer

Thank you, I appreciate the comment. This issue occurs after a hive sql query that joins around 15 tables(some of them big) so I think broadcast join do not applies, salting would imply breaking down the query and running the joins on spark functions instead of hive sql, because of the number of tables it can be time consuming, so my question is, is there any other way to force spark do distribute the partitions evenly to executors? 

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