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https://issues.apache.org/jira/browse/SPARK-18676?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hyukjin Kwon resolved SPARK-18676.
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Resolution: Incomplete
> Spark 2.x query plan data size estimation can crash join queries versus 1.x
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>
> Key: SPARK-18676
> URL: https://issues.apache.org/jira/browse/SPARK-18676
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.0.0, 2.0.1, 2.0.2, 2.1.0
> Reporter: Michael Allman
> Priority: Major
> Labels: bulk-closed
>
> Commit [c481bdf|https://github.com/apache/spark/commit/c481bdf] significantly
> modified the way Spark SQL estimates the output data size of query plans.
> I've found that—with the new table query partition pruning support in
> 2.1—this has lead to in some cases underestimation of join plan child size
> statistics to a degree that makes executing such queries impossible without
> disabling automatic broadcast conversion.
> In one case we debugged, the query planner had estimated the size of a join
> child to be 3,854 bytes. In the execution of this child query, Spark reads 20
> million rows in 1 GB of data from parquet files and shuffles 722.9 MB of
> data, outputting 17 million rows. In planning the original join query, Spark
> converts the child to a {{BroadcastExchange}}. This query execution fails
> unless automatic broadcast conversion is disabled.
> This particular query is complex and very specific to our data and schema. I
> have not yet developed a reproducible test case that can be shared. I realize
> this ticket does not give the Spark team a lot to work with to reproduce and
> test this issue, but I'm available to help. At the moment I can suggest
> running a join where one side is an aggregation selecting a few fields over a
> large table with a wide schema including many string columns.
> This issue exists in Spark 2.0, but we never encountered it because in that
> version it only manifests itself for partitioned relations read from the
> filesystem, and we rarely use this feature. We've encountered this issue in
> 2.1 because 2.1 does partition pruning for metastore tables now.
> As a back stop, we've patched our branch of Spark 2.1 to revert the
> reductions in default data type size for string, binary and user-defined
> types. We also removed the override of the statistics method in {{UnaryNode}}
> which reduces the output size of a plan based on the ratio of that plan's
> output schema size versus its children's. We have not had this problem since.
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