[jira] [Resolved] (SPARK-8359) Spark SQL Decimal type precision loss on multiplication

["Davies Liu (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-8359?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Davies Liu resolved SPARK-8359.
-------------------------------
       Resolution: Fixed
    Fix Version/s: 1.5.0

Issue resolved by pull request 6814
[https://github.com/apache/spark/pull/6814]

> Spark SQL Decimal type precision loss on multiplication
> -------------------------------------------------------
>
>                 Key: SPARK-8359
>                 URL: https://issues.apache.org/jira/browse/SPARK-8359
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 1.5.0
>            Reporter: Rene Treffer
>             Fix For: 1.5.0
>
>
> It looks like the precision of decimal can not be raised beyond ~2^112 without causing full value truncation.
> The following code computes the power of two up to a specific point
> {code}
> import org.apache.spark.sql.types.Decimal
> val one = Decimal(1)
> val two = Decimal(2)
> def pow(n : Int) :  Decimal = if (n <= 0) { one } else { 
>   val a = pow(n - 1)
>   a.changePrecision(n,0)
>   two.changePrecision(n,0)
>   a * two
> }
> (109 to 120).foreach(n => println(pow(n).toJavaBigDecimal.unscaledValue.toString))
> 649037107316853453566312041152512
> 1298074214633706907132624082305024
> 2596148429267413814265248164610048
> 5192296858534827628530496329220096
> 1038459371706965525706099265844019
> 2076918743413931051412198531688038
> 4153837486827862102824397063376076
> 8307674973655724205648794126752152
> 1661534994731144841129758825350430
> 3323069989462289682259517650700860
> 6646139978924579364519035301401720
> 1329227995784915872903807060280344
> {code}
> Beyond ~2^112 the precision is truncated even if the precision was set to n and should thus handle 10^n without problems..



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