[HIVE-4271] Limit precision of decimal type

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.11.0
• Assignee: Gunther Hagleitner Assign to me
• Reporter: Gunther Hagleitner
• Created: 01/Apr/13 08:03
• Updated: 18/May/14 07:35
• Resolved: 10/Apr/13 00:41

Description

The current decimal implementation does not limit the precision of the numbers. This has a number of drawbacks. A maximum precision would allow us to:

• Have SerDes/filformats store decimals more efficiently
• Speed up processing by implementing operations w/o generating java BigDecimals
• Simplify extending the datatype to allow for decimal(p) and decimal(p,s)
• Write a more efficient BinarySortable SerDe for sorting/grouping/joining

Exact numeric datatype are typically used to represent money, so if the limit is high enough it doesn't really become an issue.

A typical representation would pack 9 decimal digits in 4 bytes. So, with 2 longs we can represent 36 digits - which is what I propose as the limit.

Final thought: It's easier to restrict this now and have the option to do the things above than to try to do so once people start using the datatype.

Issue Links

• blocks: HIVE-4320 Consider extending max limit for precision to 38
• blocks: HIVE-4120 Implement decimal encoding for ORC
• is blocked by: HIVE-4128 Support avg(decimal)
• is related to: HIVE-2693 Add DECIMAL data type
• relates to: HIVE-5565 Limit Hive decimal type maximum precision and scale to 38