Yahui Liu created SPARK-35500:
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Summary: GenerateSafeProjection.generate will generate
SpecificSafeProjection class, but if column is array type or map type, the code
cannot be reused which impact the query performance
Key: SPARK-35500
URL: https://issues.apache.org/jira/browse/SPARK-35500
Project: Spark
Issue Type: Improvement
Components: SQL
Affects Versions: 3.1.0
Reporter: Yahui Liu
Reproduce steps:
# create a new table with array type: create table test_code_gen(a array<int>);
# Add
log4j.logger.org.apache.spark.sql.catalyst.expressions.codegen.CodeGenerator =
DEBUG to log4j.properties;
# Enter spark-shell, fire a query: spark.sql("select * from
test_code_gen").collect
# Everytime, Dataset.collect is called, SpecificSafeProjection class is
generated, but the code for the class cannot be reused because everytime the id
for two variables in the generated class is changed: MapObjects_loopValue and
MapObjects_loopIsNull. So even the class generated before has been cached, new
code cannot match the cache key so that new code need to be compiled again
which cost some time.
!image-2021-05-24-16-15-18-359.png!!image-2021-05-24-16-05-34-334.png!
# The time cost for compile is increasing with the growth of column number,
for wide table, this cost can more than 2s. !image-2021-05-24-16-11-20-841.png!
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