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

["Yanbo Liang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-4963?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14269136#comment-14269136 ] 

Yanbo Liang commented on SPARK-4963:
------------------------------------

Can anyone verify and merge this patch? It's a bug appeared frequently and fix it asap will be better.

> 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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