Weichen Xu created SPARK-22105:
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Summary: Dataframe has poor performance when computing on many
columns with codegen
Key: SPARK-22105
URL: https://issues.apache.org/jira/browse/SPARK-22105
Project: Spark
Issue Type: Improvement
Components: ML, SQL
Affects Versions: 2.3.0
Reporter: Weichen Xu
Suppose we have a dataframe with many columns (e.g 100 columns), each column is
DoubleType.
And we need to compute avg on each column. We will find using dataframe avg
will be much slower than using RDD.aggregate.
I observe this issue from this PR: (One pass imputer)
https://github.com/apache/spark/pull/18902
I also write a minimal testing code to reproduce this issue, I use computing
sum to reproduce this issue:
https://github.com/apache/spark/compare/master...WeichenXu123:aggr_test2?expand=1
When we compute `sum` on 100 `DoubleType` columns, dataframe avg will be about
3x slower than `RDD.aggregate`, but if we only compute one column, dataframe
avg will be much faster than `RDD.aggregate`.
The reason of this issue, should be the defact in dataframe codegen. Codegen
will inline everything and generate large code block. When the column number is
large (e.g 100 columns), the codegen size will be too large, which cause jvm
failed to JIT and fall back to byte code interpretation.
This PR should address this issue:
https://github.com/apache/spark/pull/19082
But we need more performance code against some code in ML after above PR
merged, to check whether this issue is actually fixed.
This JIRA used to track this performance issue.
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