Database Reference
In-Depth Information
WRONG_REDUCE=0
File Input Format Counters
Bytes Read=33485841275
File Output Format Counters
Bytes Written=90
The output includes more useful information. Before the job starts, its ID is printed; this is
needed whenever you want to refer to the job — in logfiles, for example — or when inter-
rogating it via the
mapred job
command. When the job is complete, its statistics
(known as counters) are printed out. These are very useful for confirming that the job did
what you expected. For example, for this job, we can see that 1.2 billion records were ana-
lyzed (“Map input records”), read from around 34 GB of compressed files on HDFS
(“HDFS: Number of bytes read”). The input was broken into 101 gzipped files of reason-
able size, so there was no problem with not being able to split them.
You can find out more about what the counters mean in
Built-in Counters
.
