This example uses mapreduce and accumulo to find items using regular expressions. This is accomplished using a map-only mapreduce job and a scan-time iterator.
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> createnamespace examples username@instance> createtable examples.regex username@instance examples.regex> insert dogrow dogcf dogcq dogvalue username@instance examples.regex> insert catrow catcf catcq catvalue username@instance examples.regex> quit
The RegexExample class sets an iterator on the scanner. This does pattern matching against each key/value in accumulo, and only returns matching items. It will do this in parallel and will store the results in files in hdfs.
The following will search for any rows in the input table that starts with “dog”:
$ ./bin/runmr mapreduce.RegexExample -t examples.regex --rowRegex 'dog.*' --output /tmp/output $ hdfs dfs -ls /tmp/output Found 3 items -rw-r--r-- 1 username supergroup 0 2013-01-10 14:11 /tmp/output/_SUCCESS -rw-r--r-- 1 username supergroup 51 2013-01-10 14:10 /tmp/output/part-m-00000
We can see the output of our little map-reduce job:
$ hdfs dfs -cat /tmp/output/part-m-00000 dogrow dogcf:dogcq [] 1357844987994 false dogvalue