Normal Description
There's a bug in ColumnFamilyRecordReader that appears when processing a single split (which happens in most tests that have small number of rows), and potentially in other cases. When the start and end tokens of the split are equal, duplicate rows can be returned.
Example with 5 rows:
token (start and end) = 53193025635115934196771903670925341736
Tokens returned by first get_range_slices iteration (all 5 rows):
16955237001963240173058271559858726497
40670782773005619916245995581909898190
99079589977253916124855502156832923443
144992942750327304334463589818972416113
166860289390734216023086131251507064403
Tokens returned by next iteration (first token is last token from
previous, end token is unchanged)
16955237001963240173058271559858726497
40670782773005619916245995581909898190
Tokens returned by final iteration (first token is last token from
previous, end token is unchanged)
[] (empty)
In this example, the mapper has processed 7 rows in total, 2 of which
were duplicates.