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0. Introduction
Apache Accumulo is a sorted, distributed key/value store based on Google's
BigTable design. It is built on top of Apache Hadoop, Zookeeper, and Thrift. It
features a few novel improvements on the BigTable design in the form of
cell-level access labels and a server-side programming mechanism that can modify
key/value pairs at various points in the data management process.
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1. Building
In the normal tarball or RPM release of Apache Accumulo, everything is built and
ready to go: there is no build step.
However, if you only have source code, or you wish to make changes, you need to
have maven configured to get Accumulo pre-requisites from repositories. See
the pom.xml file for the necessary components.
The libthrift 0.3 jar is no longer available from a repository. This jar will
be automatically built from the thrift tag and installed into your local maven
repository during the Accumulo build process via the
src/assemble/install-thrift-jar.sh script.
Run the following commands to build Accumulo.
tar xvzf accumulo-1.3.7-SNAPSHOT-src.tar.gz
cd accumulo-1.3.7-SNAPSHOT
mvn package && mvn assembly:single
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2. Deployment
Copy the accumulo tar file produced by "mvn package && mvn assembly:single" from
the target/ directory to the desired destination, then untar it (e.g.
tar xvzf accumulo-1.3.7-SNAPSHOT-dist.tar.gz).
If you are using the RPM, install the RPM on every machine that will run
accumulo.
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3. Configuring
Apache Accumulo has two prerequisites, Hadoop and Zookeeper. Zookeeper must be
at least version 3.3.0. Both of these must be installed and configured.
Ensure you (or the some special hadoop user account) have accounts on all of
the machines in the cluster and that hadoop and accumulo install files can be
found in the same location on every machine in the cluster. You will need to
have password-less ssh set up as described in the hadoop documentation.
You will need to have hadoop installed and configured on your system.
Apache Accumulo 1.3.7-SNAPSHOT has been tested with hadoop version
0.20.1 and 0.20.2.
Create a "slaves" file in $ACCUMULO_HOME/conf/. This is a list of machines
where tablet servers and loggers will run.
Create a "masters" file in $ACCUMULO_HOME/conf/. This is a list of
machines where the master server will run.
Create conf/accumulo-env.sh following the template of
conf/accumulo-env.sh.example. Set JAVA_HOME, HADOOP_HOME, and ZOOKEEPER_HOME.
These directories must be at the same location on every node in the cluster.
Note that zookeeper must be installed on every machine, but it should not be
run on every machine.
* Note that you will be specifying the Java heap space in accumulo-env.sh.
You should make sure that the total heap space used for the accumulo tserver,
logger and the hadoop datanode and tasktracker is less than the available
memory on each slave node in the cluster. On large clusters, it is recommended
that the accumulo master, hadoop namenode, secondary namenode, and hadoop
jobtracker all be run on separate machines to allow them to use more heap
space. If you are running these on the same machine on a small cluster, make
sure their heap space settings fit within the available memory. The zookeeper
instances are also time sensitive and should be on machines that will not be
heavily loaded, or over-subscribed for memory.
Create conf/accumulo-site.xml. You must set the zookeeper servers in this
file (instance.zookeeper.host). Look at docs/config.html to see what
additional variables you can modify and what the defaults are.
Create the write-ahead log directory on all slaves. The directory is set in
the accumulo-site.xml as the "logger.dir.walog" parameter. It is a local
directory that will be used to log updates which will be used in the event of
tablet server failure, so it is important that it have sufficient space and
reliability.
Synchronize your accumulo conf directory across the cluster. As a precaution
against mis-configured systems, servers using different configuration files
will not communicate with the rest of the cluster.
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4. Running Apache Accumulo
Make sure hadoop is configured on all of the machines in the cluster, including
access to a shared hdfs instance. Make sure hdfs is running.
Make sure zookeeper is configured and running on at least one machine in the
cluster.
Run "bin/accumulo init" to create the hdfs directory structure
(hdfs:///accumulo/*) and initial zookeeper settings. This will also allow you
to also configure the initial root password. Only do this once.
Start accumulo using the bin/start-all.sh script.
Use the "bin/accumulo shell -u <username>" command to run an accumulo shell
interpreter. Within this interpreter, run "createtable <tablename>" to create
a table, and run "table <tablename>" followed by "scan" to scan a table.
In the example below a table is created, data is inserted, and the table is
scanned.
$ ./bin/accumulo shell -u root
Enter current password for 'root'@'acu13': ******
Shell - Apache Accumulo Interactive Shell
-
- version: 1.3.7-SNAPSHOT
- instance name: acu13
- instance id: f5947fe6-081e-41a8-9877-43730c4dfc6f
-
- type 'help' for a list of available commands
-
root@ac> createtable foo
root@ac foo> insert row1 colf1 colq1 val1
root@ac foo> insert row1 colf1 colq2 val2
root@ac foo> scan
row1 colf1:colq1 [] val1
row1 colf1:colq2 [] val2
The example below start the shell, switches to table foo, and scans for a
certain column.
$ ./bin/accumulo shell -u root
Enter current password for 'root'@'acu13': ******
Shell - Apache Accumulo Interactive Shell
-
- version: 1.3.7-SNAPSHOT
- instance name: acu13
- instance id: f5947fe6-081e-41a8-9877-43730c4dfc6f
-
- type 'help' for a list of available commands
-
root@ac> table foo
root@ac foo> scan -c colf1:colq2
row1 colf1:colq2 [] val2
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5. Monitoring Apache Accumulo
You can point your browser to the master host, on port 50095 to see the status
of accumulo across the cluster. You can even do this with the text-based
browser "elinks":
$ links http://localhost:50095
From this GUI, you can ensure that tablets are assigned, tables are online,
tablet servers are up. You can monitor query and ingest rates across the
cluster.
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6. Stopping Apache Accumulo
Do not kill the tabletservers or run bin/tdown.sh unless absolutely necessary.
Recovery from a catastrophic loss of servers can take a long time. To shutdown
cleanly, run "bin/stop-all.sh" and the master will orchestrate the shutdown of
all the tablet servers. Shutdown waits for all writes to finish, so it may
take some time for particular configurations.
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7. Logging
DEBUG and above are logged to the logs/ dir. To modify this behavior change
the scripts in conf/. To change the logging dir, set ACCUMULO_LOG_DIR in
conf/accumulo-env.sh. Stdout and stderr of each accumulo process is
redirected to the log dir.
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8. API
The public accumulo API is composed of everything in the
org.apache.accumulo.core.client package (excluding the
org.apache.accumulo.core.client.impl package) and the following classes from
org.apache.accumulo.core.data : Key, Mutation, Value, and Range. To get started
using accumulo review the example and the javadoc for the packages and classes
mentioned above.
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9. Performance Tuning
Accumulo has exposed several configuration properties that can be changed.
These properties and configuration management are described in detail in
docs/config.html. While the default value is usually optimal, there are cases
where a change can increase query and ingest performance.
Before changing a property from its default in a production system, you should
develop a good understanding of the property and consider creating a test to
prove the increased performance.
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