[IMPALA-5936] Difference between the % Operator and Mod function with large decimal values

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: Impala 2.11.0
• Component/s: Frontend
• Epic Color: ghx-label-1
• Assignee: Zoltán Borók-Nagy
• Reporter: Jason Phelps
• Created: 14/Sep/17 19:18
• Updated: 29/Nov/17 17:31
• Resolved: 29/Nov/17 10:36

Description

It looks like the '%' operator breaks in the following scenario:

decimal(18,0) + Any value greater than INT (2147483647)

As far as I can tell, `%` will typically use the proper mod function transparently, but instead of using/casting as BIGINT, it will use INT, and then overflow. If I directly cast as BIGINT, it will work as expected.

num	num % 3	mod(num, 3)
42607032167	-2	2
42606774111	-1	0
42363009429	-1	0
42603003271	0	1
42606961501	0	1
42608445511	0	1
42607368197	-2	2
42606319059	-1	0
42602678339	-2	2
42260146355	-2	2

If the number is used directly (i.e. not using a column), it works as expected:

42607032167 % 3	mod(42607032167, 3)
2	2

According to the documentation, these should be equivalent

mod(numeric_type a, same_type b)
Purpose: Returns the modulus of a number. Equivalent to the % arithmetic operator. Works with any size integer type, any size floating-point type, and DECIMAL with any precision and scale.

Issue Links

• is related to: IMPALA-1879 mod() function doesn't always interpret fractional arguments as DECIMAL