[jira] [Resolved] (SPARK-18738) Some Spark SQL queries has poor performance on HDFS Erasure Coding feature when enabling dynamic allocation.

["Sean Owen (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-18738?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sean Owen resolved SPARK-18738.
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    Resolution: Not A Problem

I am going to close this as not a problem unless there's more info here ... clearly the problem is data locality being lower in the EC case. You can still tune Spark to not mind locality and possibly use all the executors, but 2/3 of the tasks are having to read data remotely then, which is its own overhead. It's not clear why only 1/3 of your machines appears to have data available for local execution. This also makes me wonder if you literally have 3x fewer data nodes in the EC case.

> Some Spark SQL queries has poor performance on HDFS Erasure Coding feature when enabling dynamic allocation.
> ------------------------------------------------------------------------------------------------------------
>
>                 Key: SPARK-18738
>                 URL: https://issues.apache.org/jira/browse/SPARK-18738
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 2.0.2
>            Reporter: Lifeng Wang
>
> We run TPCx-BB with Spark SQL engine on local cluster using Spark 2.0.3 trunk and Hadoop 3.0 alpha 2 trunk. We run Spark SQL queries with same data size on both Erasure Coding and 3-replication.  The test results show that some queries has much worse performance on EC compared to 3-replication. After initial investigations, we found spark starts one third executors to execute queries on EC compared to 3-replication. 
> We use query 30 as example, our cluster can totally launch 108 executors. When we run the query from 3-replication database, spark will start all 108 executors to execute the query.  When we run the query from Erasure Coding database, spark will launch 108 executors and kill 72 executors due to they’re idle, at last there are only 36 executors to execute the query which leads to poor performance.
> This issue only happens when we enable dynamic allocations mechanism. When we disable the dynamic allocations, Spark SQL query on EC has the similar performance with on 3-replication.



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