S Daniel Zafar created SPARK-31137:
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Summary: Opportunity to simplify execution plan when passing empty
dataframes to subtract()
Key: SPARK-31137
URL: https://issues.apache.org/jira/browse/SPARK-31137
Project: Spark
Issue Type: Improvement
Components: PySpark, SQL
Affects Versions: 2.4.5
Reporter: S Daniel Zafar
Execution plans are similar when passing an empty versus non-empty DataFrame to
pyspark's subtract call.
{code:java}
df.subtract(regDf){code}
yields the same physical plan as:
{code:java}
df.subtract(emptyDf){code}
Since the operation (EXCEPT DISTINCT in Spark SQL) requires a sort on both
DataFrames, this can yield some significant performance speed-ups because if
the incoming DF is empty no processing should happen.
Should be a quick fix for a seasoned commiter.
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