Apache Accumulo™

Title: Apache Accumulo Table-to-File Example Notice: Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at . http://www.apache.org/licenses/LICENSE-2.0 . Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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:

$ ./bin/accumulo shell -u username -p password
Shell - Apache Accumulo Interactive Shell
- version: 1.5.0
- instance name: instance
- instance id: 00000000-0000-0000-0000-000000000000
- type 'help' for a list of available commands
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/tool.sh lib/accumulo-examples-simple.jar org.apache.accumulo.examples.simple.mapreduce.TableToFile -u user -p passwd -i instance -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/output/part-m-00000
catrow cf:cq []	catvalue
dogrow cf:cq []	dogvalue