[VL][1.2] Result of cast(double as string) is inconsistent with vanilla spark

[wForget]

Backend

VL (Velox)

Bug description

sql:

create table t1 as select cast(0.000642224797047674666 as double) as c1;
select cast(c1 as string) from t1;

vanilla spark result:

6.422247970476747E-4

gluten 1.2.0 with velox result:

6.4222479704767466E-4

Spark version

Spark-3.5.x

Spark configurations

No response

System information

No response

Relevant logs

No response

[zhouyuan]

This is due to the double precision issue - in short, double precision is not enough and might change(2 == 1.9999999). Is it possible to switch to decimal data type in this case?

CC @rui-mo

[wForget]

This is due to the double precision issue - in short, double precision is not enough and might change(2 == 1.9999999). Is it possible to switch to decimal data type in this case?

This issue may not be because the double precision is not enough, it happens in cast double to string, I guess it is because the precision of the double to string formatter is not aligned.

[rui-mo]

The related code is: https://github.com/facebookincubator/velox/blob/264ccdfcbc26f8fb56258cb7031f6cba915013ea/velox/type/Conversions.h#L562-L587. And would you like to try to reproduce it in Velox with a unit test? Thanks.

[wForget]

The related code is: https://github.com/facebookincubator/velox/blob/264ccdfcbc26f8fb56258cb7031f6cba915013ea/velox/type/Conversions.h#L562-L587. And would you like to try to reproduce it in Velox with a unit test? Thanks.

Thank you for the information, I will try to add unit test in velox.