Details
Trivial Description
Consider an Avro File of a single record type with about 70 fields in the order (str, str, str, long, str, double, [lets take only first 6 into consideration] ...).
To pass this into a simple MapReduce job I do: AvroInputFormat.addInputPath(...) and it works well with an IdentityMapper.
Now I'd like to read only three fields, say fields 0, 1 and 3 so I give the special schema with my 3 fields as (str (0), str (1), long(2)) using AvroJob.setInputGeneric(..., mySchema). This leads to a failure of the mapreduce job since the Avro record reader reads the file for its entire schema (of 70 fields) and tries to convert my given 'long' field to 'str' as is at the index 2 of the actual schema (meaning its using the actual schema embedded into the file, not what I supplied!).
The AvroRecordReader must support reading in the schema specified by the user using AvroJob.setInputGeneric.
I've written a patch for it to do the same but am not sure if its actually the solution (MAP_OUTPUT_SCHEMA use?)