David Vogelbacher created SPARK-24957:
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Summary: Decimal arithmetic can lead to wrong values using codegen
Key: SPARK-24957
URL: https://issues.apache.org/jira/browse/SPARK-24957
Project: Spark
Issue Type: Bug
Components: SQL
Affects Versions: 2.3.1
Reporter: David Vogelbacher
I noticed a bug when doing arithmetic on a dataframe containing decimal values
with codegen enabled.
I tried to narrow it down on a small repro and got this (executed in
spark-shell):
{noformat}
scala> val df = Seq(
| ("a", BigDecimal("12.0")),
| ("a", BigDecimal("12.0")),
| ("a", BigDecimal("11.9999999988")),
| ("a", BigDecimal("12.0")),
| ("a", BigDecimal("12.0")),
| ("a", BigDecimal("11.9999999988")),
| ("a", BigDecimal("11.9999999988"))
| ).toDF("text", "number")
df: org.apache.spark.sql.DataFrame = [text: string, number: decimal(38,18)]
scala> val df_grouped_1 =
df.groupBy(df.col("text")).agg(functions.avg(df.col("number")).as("number"))
df_grouped_1: org.apache.spark.sql.DataFrame = [text: string, number:
decimal(38,22)]
scala> df_grouped_1.collect()
res0: Array[org.apache.spark.sql.Row] = Array([a,11.9999999994857142857143])
scala> val df_grouped_2 =
df_grouped_1.groupBy(df_grouped_1.col("text")).agg(functions.sum(df_grouped_1.col("number")).as("number"))
df_grouped_2: org.apache.spark.sql.DataFrame = [text: string, number:
decimal(38,22)]
scala> df_grouped_2.collect()
res1: Array[org.apache.spark.sql.Row] =
Array([a,1199999999948571.4285714285714285714286])
scala> val df_total_sum =
df_grouped_1.agg(functions.sum(df_grouped_1.col("number")).as("number"))
df_total_sum: org.apache.spark.sql.DataFrame = [number: decimal(38,22)]
scala> df_total_sum.collect()
res2: Array[org.apache.spark.sql.Row] = Array([11.9999999994857142857143])
{noformat}
The results of {{df_grouped_1}} and {{df_total_sum}} are correct, whereas the
result of {{df_grouped_2}} is clearly incorrect (it is the value of the correct
result times {{10^14}}).
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