[jira] [Comment Edited] (SPARK-4963) SchemaRDD.sample may return wrong results

["Cheng Lian (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-4963?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14260790#comment-14260790 ] 

Cheng Lian edited comment on SPARK-4963 at 12/30/14 4:49 AM:
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OK I agree. However the {{\_.copy()}} call should be added in the SQL {{Sample}} operator rather than Spark's {{RDD.sample}} method, since the element type of an arbitrary RDD doesn't necessarily to be a {{Product}} and {{\_.copy()}} is not available.


was (Author: lian cheng):
OK I agree. However the {{_.copy()}} call should be added in the SQL {{Sample}} operator rather than Spark's {{RDD.sample}} method, since the element type of an arbitrary RDD doesn't necessarily to be a {{Product}} and {{_.copy()}} is not available.

> SchemaRDD.sample may return wrong results
> -----------------------------------------
>
>                 Key: SPARK-4963
>                 URL: https://issues.apache.org/jira/browse/SPARK-4963
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 1.2.0
>            Reporter: Cheng Lian
>            Assignee: Yanbo Liang
>
> This {{sbt/sbt hive/console}} session can easily reproduce this issue:
> {code}
> sql("SELECT * FROM src WHERE key % 2 = 0").
>   sample(withReplacement = false, fraction = 0.05).
>   registerTempTable("sampled")
> println(table("sampled").queryExecution)
> val query = sql("SELECT * FROM sampled WHERE key % 2 = 1")
> println(query.queryExecution)
> // Should print `true'
> println((1 to 10).map(_ => query.collect().isEmpty).reduce(_ && _))
> {code}
> Notice that when fraction is less than 0.4, {{GapSamplingIterator}} is used to do the sampling. My guess is that there’s something to do with the underlying mutable row objects used in {{HiveTableScan}}, but haven't figured out the root cause.



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