Apache Accumulo Table-to-File Example

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
root@instance> createnamespace examples
root@instance> createtable examples.input
root@instance examples.input> insert dog cf cq dogvalue
root@instance examples.input> insert cat cf cq catvalue
root@instance examples.input> insert junk family qualifier junkvalue
root@instance examples.input> 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 exampmles.input --columns cf:cq --output /tmp/output

$ hadoop fs -ls /tmp/output
Found 2 items
-rw-r--r--   3 root supergroup          0 2021-05-04 10:32 /tmp/output/_SUCCESS
-rw-r--r--   3 root supergroup         44 2021-05-04 10:32 /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