If I have speculative execution turned on, the following script fails:
a = load 'studenttab20m' as (name, age, gpa);
b = load 'votertab10k' as (name, age, registration, contributions);
c = filter a by age < '50';
d = filter b by age < '50';
e = cogroup c by (name, age), d by (name, age) parallel 10;
f = foreach e generate flatten(c), flatten(d) parallel 10;
g = group f by registration parallel 10;
h = foreach g generate group, SUM(f.d::contributions) parallel 10;
i = order h by ($1, $0);
store i into 'out';
I traced this to the fact that the first MR job produces one or more empty outputs from the reducer. This happened on the reducers that happened to have second task running.
I am not sure what the issue is and I am working with hadoop guys to investigate. Until this issue is resolved, I would like to trun speculative execution off.