Tejas Patil created SPARK-19843:
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Summary: UTF8String => (int / long) conversion expensive for
invalid inputs
Key: SPARK-19843
URL: https://issues.apache.org/jira/browse/SPARK-19843
Project: Spark
Issue Type: Improvement
Components: SQL
Affects Versions: 2.1.0
Reporter: Tejas Patil
In case of invalid inputs, converting a UTF8String to int or long returns null.
This comes at a cost wherein the method for conversion (e.g [0]) would throw an
exception. Exception handling is expensive as it will convert the UTF8String
into a java string, populate the stack trace (which is a native call). While
migrating workloads from Hive -> Spark, I see that this at an aggregate level
affects the performance of queries in comparison with hive.
The exception is just indicating that the conversion failed.. its not
propagated to users so it would be good to avoid.
Couple of options:
- Return Integer / Long (instead of primitive types) which can be set to NULL
if the conversion fails. This is boxing and super bad for perf so a big no.
- Hive has a pre-check [1] for this which is not a perfect safety net but
helpful to capture typical bad inputs eg. empty string, "null".
[0] :
https://github.com/apache/spark/blob/4ba9c6c453606f5e5a1e324d5f933d2c9307a604/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java#L950
[1] :
https://github.com/apache/hive/blob/ff67cdda1c538dc65087878eeba3e165cf3230f4/serde/src/java/org/apache/hadoop/hive/serde2/lazy/LazyUtils.java#L90
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