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Posted to issues@spark.apache.org by "Apache Spark (JIRA)" <ji...@apache.org> on 2016/10/17 18:14:58 UTC
[jira] [Commented] (SPARK-17972) Query planning slows down
dramatically for large query plans even when sub-trees are cached
[ https://issues.apache.org/jira/browse/SPARK-17972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15582977#comment-15582977 ]
Apache Spark commented on SPARK-17972:
--------------------------------------
User 'liancheng' has created a pull request for this issue:
https://github.com/apache/spark/pull/15517
> Query planning slows down dramatically for large query plans even when sub-trees are cached
> -------------------------------------------------------------------------------------------
>
> Key: SPARK-17972
> URL: https://issues.apache.org/jira/browse/SPARK-17972
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 1.6.2, 2.0.1
> Reporter: Cheng Lian
> Assignee: Cheng Lian
>
> The following Spark shell snippet creates a series of query plans that grow exponentially. The {{i}}-th plan is created using 4 *cached* copies of the {{i - 1}}-th plan.
> {code}
> (0 until 6).foldLeft(Seq(1, 2, 3).toDS) { (plan, iteration) =>
> val start = System.currentTimeMillis()
> val result = plan.join(plan, "value").join(plan, "value").join(plan, "value").join(plan, "value")
> result.cache()
> System.out.println(s"Iteration $iteration takes time ${System.currentTimeMillis() - start} ms")
> result.as[Int]
> }
> {code}
> We can see that although all plans are cached, the query planning time still grows exponentially and quickly becomes unbearable.
> {noformat}
> Iteration 0 takes time 9 ms
> Iteration 1 takes time 19 ms
> Iteration 2 takes time 61 ms
> Iteration 3 takes time 219 ms
> Iteration 4 takes time 830 ms
> Iteration 5 takes time 4080 ms
> {noformat}
> Similar scenarios can be found in iterative ML code and significantly affects usability.
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