[HIVE-5356] Move arithmatic UDFs to generic UDF implementations

• Type: Task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.11.0
• Fix Version/s: 0.13.0
• Component/s: UDF
• Hadoop Flags: Incompatible change
• Assignee: Xuefu Zhang
• Reporter: Xuefu Zhang
• Created: 25/Sep/13 04:40
• Updated: 13/Dec/13 19:40
• Resolved: 20/Nov/13 05:42

Description

Currently, all of the arithmetic operators, such as add/sub/mult/div, are implemented as old-style UDFs and java reflection is used to determine the return type TypeInfos/ObjectInspectors, based on the return type of the evaluate() method chosen for the expression. This works fine for types that don't have type params.

Hive decimal type participates in these operations just like int or double. Different from double or int, however, decimal has precision and scale, which cannot be determined by just looking at the return type (decimal) of the UDF evaluate() method, even though the operands have certain precision/scale. With the default of "decimal" without precision/scale, then (10, 0) will be the type params. This is certainly not desirable.

To solve this problem, all of the arithmetic operators would need to be implemented as GenericUDFs, which allow returning ObjectInspector during the initialize() method. The object inspectors returned can carry type params, from which the "exact" return type can be determined.

It's worth mentioning that, for user UDF implemented in non-generic way, if the return type of the chosen evaluate() method is decimal, the return type actually has (10,0) as precision/scale, which might not be desirable. This needs to be documented.

This JIRA will cover minus, plus, divide, multiply, mod, and pmod, to limit the scope of review. The remaining ones will be covered under HIVE-5706.

Issue Links

• incorporates: HIVE-4523 round() function with specified decimal places not consistent with mysql
• incorporates: HIVE-5706 Move a few numeric UDFs to generic implementations
• is part of: HIVE-3976 Support specifying scale and precision with Hive decimal type
• is related to: HIVE-5996 Query for sum of a long column of a table with only two rows produces wrong result
• is related to: HIVE-5878 Hive standard avg UDAF returns double as the return type for some exact input types
• relates to: HIVE-5918 int / int division does not vectorize due to type checks
• relates to: HIVE-6012 restore backward compatibility of arithmetic operations
• relates to: HIVE-5748 Revisit all data types and numeric operators to align Hive with SQL standard or other DB's implementation
• requires: HIVE-5726 The DecimalTypeInfo instance associated with a decimal constant is not in line with the precision/scale of the constant
• links to: https://reviews.apache.org/r/15113/