[PIG-4724] GROUP ALL must create an output record in case there is no input

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 0.16.0
• Assignee: Prashant Kommireddi
• Reporter: Prashant Kommireddi
• Created: 03/Nov/15 20:05
• Updated: 05/May/16 06:46

Description

A = load 'data';

B = filter A by $0 == 'THIS_DOES_NOT_EXIST';

C = group B ALL;

D = foreach C generate group, COUNT(B);

Even if the filter did not output any rows, since we are grouping on ALL the expected output should probably be (ALL, 0). The implementation generates a pseudo key “all” for every input on map side, thus reduce side we can combine all input together. However, this does not work for 0 input since the reduce side does not get any input. If the input is empty, yield a pseudo “all, 0” to reduce