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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 accumulo, everything is built and
ready to go on x86 GNU/Linux: 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 prerequisites from repositories.  See
the pom.xml file for the necessary components. Activate the 'docs' profile to build
the Accumulo developer and user manual.

Run "mvn package -P assemble" to build a distribution, or run "mvn package -P assemble,docs"
to also build the documentation.

If you are running on another Unix-like operating system (OSX, etc) then
you may wish to build the native libraries.  They are not strictly necessary
but having them available suppresses a runtime warning:

  $ ( cd ./src/server/src/main/c++ ; make )

If you want to build the debian release, use the command "mvn install -Pdeb" to 
generate the .deb files in the target/ directory. Please follow the steps at 
https://cwiki.apache.org/BIGTOP/how-to-install-hadoop-distribution-from-bigtop.html
to add bigtop to your debian sources list. This will make it substantially
easier to install.

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2. Deployment

Copy the accumulo tar file produced by mvn package from the src/assemble/target/
directory to the desired destination, then untar it (e.g. 
tar xvzf accumulo-1.5.0-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. Upgrading from 1.3 to 1.4

There are no steps for upgrading from 1.3 to 1.4.

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4. 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. 
Zookeeper normally only allows for 10 connections from one computer.  On a 
single-host install, this number is a little too low.  Add the following to the 
$ZOOKEEPER_HOME/conf/zoo.cfg file:

   maxClientCnxns=100

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.  Accumulo
1.5.0-SNAPSHOT has been tested with hadoop version 0.20.2.  To avoid data loss,
you must enable HDFS durable sync.  How you enable this depends on your version
of Hadoop.  For older versions of Hadoop set dfs.support.append to true in
hdfs-site.xml.  For newer versions set dfs.durable.sync to true.  After setting
these properties restart HDFS.  See ACCUMULO-623 for more information.

The example accumulo configuration files are placed in directories based on the 
memory footprint for the accumulo processes.  If you are using native libraries
for you tablet server in-memory map, then you can use the files in "native-standalone".
If you get warnings about not being able to load the native libraries, you can
use the configuration files in "standalone".

For testing on a single computer, use a fairly small configuration:

  $ cp conf/examples/512MB/native-standalone/* conf

Please note that the footprints are for only the Accumulo system processes, so 
ample space should be left for other processes like hadoop, zookeeper, and the 
accumulo client code.  These directories must be at the same location on every 
node in the cluster.

If you are configuring a larger cluster you will need to create the configuration
files yourself and propogate the changes to the $ACCUMULO_HOME/conf directories:

   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
   example/3GB/native-standalone/accumulo-env.sh.  

However you create your configuration files, you will need to set 
JAVA_HOME, HADOOP_HOME, and ZOOKEEPER_HOME in conf/accumulo-env.sh

Note that zookeeper client jar files must be installed on every machine, but 
the server should not be run on every machine.

Create the $ACCUMULO_LOG_DIR on every machine in the slaves file.

* 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.

Edit 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.

It is advisable to change the instance secret (instance.secret) to some new
value.  Also ensure that the accumulo-site.xml file is not readable by other
users on the machine.

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.  It is possible to specify a comma-separated list of directories 
to use for write-ahead logs, in which case each directory in the list must be
created on all slaves.

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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5. 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'@'accumulo': ******

    Shell - Apache Accumulo Interactive Shell
    - 
    - version: 1.5.0-SNAPSHOT
    - instance name: accumulo
    - 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'@'accumulo': ******

    Shell - Apache Accumulo Interactive Shell
    - 
    - version: 1.5.0-SNAPSHOT
    - instance name: accumulo
    - 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


If you are running on top of hdfs with kerberos enabled, then you need to do
some extra work. First, create an Accumulo principal

  kadmin.local -q "addprinc -randkey accumulo/<host.domain.name>"

where <host.domain.name> is replaced by a fully qualified domain name. Export
the principals to a keytab file. It is safer to create a unique keytab file for each
server, but you can also glob them if you wish.

  kadmin.local -q "xst -k accumulo.keytab -glob accumulo*"

Place this file in $ACCUMULO_HOME/conf for every host. It should be owned by
the accumulo user and chmodded to 400. Add the following to the accumulo-env.sh

In the accumulo-site.xml file on each node, add settings for general.kerberos.keytab
and general.kerberos.principal, where the keytab setting is the absolute path
to the keytab file ($ACCUMULO_HOME is valid to use) and principal is set to
accumulo/_HOST@<REALM>, where REALM is set to your kerberos realm. You may use
_HOST in lieu of your individual host names.

  <property>
    <name>general.kerberos.keytab</name>
    <value>$ACCUMULO_HOME/conf/accumulo.keytab</value>
  </property>

  <property>
    <name>general.kerberos.principal</name>
    <value>accumulo/_HOST@MYREALM</value>
  </property> 

You can then start up Accumulo as you would with the accumulo user, and it will
automatically handle the kerberos keys needed to access hdfs.

Please Note: You may have issues initializing Accumulo while running kerberos HDFS.
You can resolve this by temporarily granting the accumulo user write access to the
hdfs root directory, running init, and then revoking write permission in the root 
directory (be sure to maintain access to the /accumulo directory).

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6. 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 "links":

 $ 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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7. 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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8. 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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9. 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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10. Performance Tuning

Apache 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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