This example uses mapreduce to extract specified columns from an existing table.
To run this example you will need some data in a table. The following will put a trivial amount of data into accumulo using the accumulo shell:
$ accumulo shell username@instance> createtable input username@instance> insert dog cf cq dogvalue username@instance> insert cat cf cq catvalue username@instance> insert junk family qualifier junkvalue username@instance> quit
The TableToFile class configures a map-only job to read the specified columns and write the key/value pairs to a file in HDFS.
The following will extract the rows containing the column “cf:cq”:
$ ./bin/runmr mapreduce.TableToFile -t input --columns cf:cq --output /tmp/output $ hadoop fs -ls /tmp/output -rw-r--r-- 1 username supergroup 0 2013-01-10 14:44 /tmp/output/_SUCCESS drwxr-xr-x - username supergroup 0 2013-01-10 14:44 /tmp/output/_logs drwxr-xr-x - username supergroup 0 2013-01-10 14:44 /tmp/output/_logs/history -rw-r--r-- 1 username supergroup 9049 2013-01-10 14:44 /tmp/output/_logs/history/job_201301081658_0011_1357847072863_username_TableToFile%5F1357847071434 -rw-r--r-- 1 username supergroup 26172 2013-01-10 14:44 /tmp/output/_logs/history/job_201301081658_0011_conf.xml -rw-r--r-- 1 username supergroup 50 2013-01-10 14:44 /tmp/output/part-m-00000
We can see the output of our little map-reduce job:
$ hadoop fs -text /tmp/output/part-m-00000 catrow cf:cq [] catvalue dogrow cf:cq [] dogvalue $