问题
I am able to find the name if the input file in a mapper class using FileSplit when writing the program in Java.
Is there a corresponding way to do this when I write a program in Python (using streaming?)
I found the following in the hadoop streaming document on apache:
See Configured Parameters. During the execution of a streaming job, the names of the "mapred" parameters are transformed. The dots ( . ) become underscores ( _ ). For example, mapred.job.id becomes mapred_job_id and mapred.jar becomes mapred_jar. In your code, use the parameter names with the underscores.
But I still cant understand how to make use of this inside my mapper.
Any help is highly appreciated.
Thanks
回答1:
According to the "Hadoop : The Definitive Guide"
Hadoop sets job configuration parameters as environment variables for Streaming programs. However, it replaces non-alphanumeric character with underscores to make sure they are valid names. The following Python expression illustrates how you can retrieve the value of the mapred.job.id property from within a Python Streaming script:
os.environ["mapred_job_id"]
You can also set environment variables for the Streaming process launched by MapReduce by applying the -cmdenv option to the Streaming launcher program (once for each variable you wish to set). For example, the following sets the MAGIC_PARAMETER environment variable:
-cmdenv MAGIC_PARAMETER=abracadabra
回答2:
By parsing the mapreduce_map_input_file(new) or map_input_file
Notice:
The two environment variables are case-sensitive, all letters are lower-case.
回答3:
The new ENV_VARIABLE for Hadoop 2.x is MAPREDUCE_MAP_INPUT_FILE
来源：https://stackoverflow.com/questions/7449756/get-input-file-name-in-streaming-hadoop-program