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<head>
    <title>HBase</title>
</head>
<body bgcolor="white">
<a href="http://hbase.org">HBase</a> is a scalable, distributed database built on <a href="http://hadoop.apache.org/core">Hadoop Core</a>.

<h2>Table of Contents</h2>
<ul>
<li>
  <a href="#requirements">Requirements</a>
  <ul>
    <li><a href="#windows">Windows</a></li>
  </ul>
</li>
<li>
  <a href="#getting_started" >Getting Started</a>
  <ul>
    <li><a href="#standalone">Standalone</a></li>
    <li>
      <a href="#distributed">Distributed Operation: Pseudo- and Fully-distributed modes</a>
      <ul>
        <li><a href="#pseudo-distrib">Pseudo-distributed</a></li>
        <li><a href="#fully-distrib">Fully-distributed</a></li>
      </ul>
    </li>
  </ul>
</li>
<li><a href="#runandconfirm">Running and Confirming Your Installation</a></li>
<li><a href="#upgrading" >Upgrading</a></li>
<li><a href="#client_example">Example API Usage</a></li>
<li><a href="#related" >Related Documentation</a></li>
</ul>

<h2><a name="requirements">Requirements</a></h2>
<ul>
  <li>Java 1.6.x, preferably from <a href="http://www.java.com/download/">Sun</a>. Use the latest version available except u18 (u19 is fine).</li>
  <li>This version of HBase will only run on <a href="http://hadoop.apache.org/common/releases.html">Hadoop 0.20.x</a>.
 HBase will lose data unless it is running on an HDFS that has a durable sync operation.
 Currently only the <a href="http://svn.apache.org/viewvc/hadoop/common/branches/branch-0.20-append/">branch-0.20-append</a>
 branch has this attribute.  No official releases have been made from this branch as of this writing
 so you will have to build your own Hadoop from the tip of this branch
 (or install Cloudera's <a href="http://archive.cloudera.com/docs/">CDH3</a> (as of this writing, it is in beta); it has the
 0.20-append patches needed to add a durable sync).
 See <a href="http://svn.apache.org/viewvc/hadoop/common/branches/branch-0.20-append/CHANGES.txt">CHANGES.txt</a>
 in branch-0.20.-append to see list of patches involved.</li>
  <li>
    <em>ssh</em> must be installed and <em>sshd</em> must be running to use Hadoop's scripts to manage remote Hadoop daemons.
   You must be able to ssh to all nodes, including your local node, using passwordless login
   (Google "ssh passwordless login").
  </li>
  <li>
    HBase depends on <a href="http://hadoop.apache.org/zookeeper/">ZooKeeper</a> as of release 0.20.0.
    HBase keeps the location of its root table, who the current master is, and what regions are
    currently participating in the cluster in ZooKeeper.
    Clients and Servers now must know their <em>ZooKeeper Quorum locations</em> before
    they can do anything else (Usually they pick up this information from configuration
    supplied on their CLASSPATH). By default, HBase will manage a single ZooKeeper instance for you.
    In <em>standalone</em> and <em>pseudo-distributed</em> modes this is usually enough, but for
    <em>fully-distributed</em> mode you should configure a ZooKeeper quorum (more info below).
  </li>
  <li>Hosts must be able to resolve the fully-qualified domain name of the master.</li>
  <li>
    The clocks on cluster members should be in basic alignments. Some skew is tolerable but
    wild skew could generate odd behaviors. Run <a href="http://en.wikipedia.org/wiki/Network_Time_Protocol">NTP</a>
    on your cluster, or an equivalent.
  </li>
  <li>
    The default <b>ulimit -n</b> of 1024 on *nix systems will be insufficient.
    Any significant amount of loading will lead you to
    <a href="http://wiki.apache.org/hadoop/Hbase/FAQ#A6">FAQ: Why do I see "java.io.IOException...(Too many open files)" in my logs?</a>.
    You will also notice errors like:
    <pre>
2010-04-06 03:04:37,542 INFO org.apache.hadoop.hdfs.DFSClient: Exception increateBlockOutputStream java.io.EOFException
2010-04-06 03:04:37,542 INFO org.apache.hadoop.hdfs.DFSClient: Abandoning block blk_-6935524980745310745_1391901
    </pre>
    Do yourself a favor and change this to more than 10k. See the FAQ in the hbase wiki for how.
    Also, HDFS has an upper bound of files that it can serve at the same time,
    called xcievers (yes, this is <em>misspelled</em>). Again, before doing any loading,
    make sure you configured Hadoop's conf/hdfs-site.xml with this:
    <pre>
&lt;property&gt;
  &lt;name&gt;dfs.datanode.max.xcievers&lt;/name&gt;
  &lt;value&gt;2047&lt;/value&gt;
&lt;/property&gt;
    </pre>
    See the background of this issue here: <a href="http://wiki.apache.org/hadoop/Hbase/Troubleshooting#A5">Problem: "xceiverCount 258 exceeds the limit of concurrent xcievers 256"</a>.
    Failure to follow these instructions will result in <b>data loss</b>.
  </li>
</ul>

<h3><a name="windows">Windows</a></h3>
If you are running HBase on Windows, you must install
<a href="http://cygwin.com/">Cygwin</a>
to have a *nix-like environment for the shell scripts. The full details
are explained in 
the <a href="../cygwin.html">Windows Installation</a>
guide.


<h2><a name="getting_started" >Getting Started</a></h2>
<p>What follows presumes you have obtained a copy of HBase,
see <a href="http://hadoop.apache.org/hbase/releases.html">Releases</a>, and are installing
for the first time. If upgrading your HBase instance, see <a href="#upgrading">Upgrading</a>.</p>

<p>Three modes are described: <em>standalone</em>, <em>pseudo-distributed</em> (where all servers are run on
a single host), and <em>fully-distributed</em>. If new to HBase start by following the standalone instructions.</p>

<p>Begin by reading <a href="#requirements">Requirements</a>.</p>

<p>Whatever your mode, define <code>${HBASE_HOME}</code> to be the location of the root of your HBase installation, e.g.
<code>/user/local/hbase</code>. Edit <code>${HBASE_HOME}/conf/hbase-env.sh</code>. In this file you can
set the heapsize for HBase, etc. At a minimum, set <code>JAVA_HOME</code> to point at the root of
your Java installation.</p>

<h3><a name="standalone">Standalone mode</a></h3>
<p>If you are running a standalone operation, there should be nothing further to configure; proceed to
<a href="#runandconfirm">Running and Confirming Your Installation</a>. If you are running a distributed
operation, continue reading.</p>

<h3><a name="distributed">Distributed Operation: Pseudo- and Fully-distributed modes</a></h3>
<p>Distributed modes require an instance of the <em>Hadoop Distributed File System</em> (DFS).
See the Hadoop <a href="http://hadoop.apache.org/common/docs/r0.20.1/api/overview-summary.html#overview_description">
requirements and instructions</a> for how to set up a DFS.</p>

<h4><a name="pseudo-distrib">Pseudo-distributed mode</a></h4>
<p>A pseudo-distributed mode is simply a distributed mode run on a single host.
Use this configuration testing and prototyping on hbase.  Do not use this configuration
for production nor for evaluating HBase performance.
</p>
<p>Once you have confirmed your DFS setup, configuring HBase for use on one host requires modification of
<code>${HBASE_HOME}/conf/hbase-site.xml</code>, which needs to be pointed at the running Hadoop DFS instance.
Use <code>hbase-site.xml</code> to override the properties defined in
<code>${HBASE_HOME}/conf/hbase-default.xml</code> (<code>hbase-default.xml</code> itself
should never be modified) and for HDFS client configurations.
At a minimum, the <code>hbase.rootdir</code>,
which points HBase at the Hadoop filesystem to use,
and the <code>dfs.replication</code>, an hdfs client-side
configuration stipulating how many replicas to keep up,
should be redefined in <code>hbase-site.xml</code>. For example,
adding the properties below to your <code>hbase-site.xml</code> says that HBase
should use the <code>/hbase</code> 
directory in the HDFS whose namenode is at port 9000 on your local machine, and that
it should run with one replica only (recommended for pseudo-distributed mode):</p>
<blockquote>
<pre>
&lt;configuration&gt;
  ...
  &lt;property&gt;
    &lt;name&gt;hbase.rootdir&lt;/name&gt;
    &lt;value&gt;hdfs://localhost:9000/hbase&lt;/value&gt;
    &lt;description&gt;The directory shared by region servers.
    &lt;/description&gt;
  &lt;/property&gt;
  &lt;property&gt;
    &lt;name&gt;dfs.replication&lt;/name&gt;
    &lt;value&gt;1&lt;/value&gt;
    &lt;description&gt;The replication count for HLog &amp; HFile storage. Should not be greater than HDFS datanode count.
    &lt;/description&gt;
  &lt;/property&gt;
  ...
&lt;/configuration&gt;
</pre>
</blockquote>

<p>Note: Let HBase create the directory. If you don't, you'll get warning saying HBase
needs a migration run because the directory is missing files expected by HBase (it'll
create them if you let it).</p>
<p>Also Note: Above we bind to localhost.  This means that a remote client cannot
connect.  Amend accordingly, if you want to connect from a remote location.</p>

<h4><a name="fully-distrib">Fully-Distributed Operation</a></h4>
<p>For running a fully-distributed operation on more than one host, the following
configurations must be made <em>in addition</em> to those described in the
<a href="#pseudo-distrib">pseudo-distributed operation</a> section above.</p>

<p>In <code>hbase-site.xml</code>, set <code>hbase.cluster.distributed</code> to <code>true</code>.</p>
<blockquote>
<pre>
&lt;configuration&gt;
  ...
  &lt;property&gt;
    &lt;name&gt;hbase.cluster.distributed&lt;/name&gt;
    &lt;value&gt;true&lt;/value&gt;
    &lt;description&gt;The mode the cluster will be in. Possible values are
      false: standalone and pseudo-distributed setups with managed Zookeeper
      true: fully-distributed with unmanaged Zookeeper Quorum (see hbase-env.sh)
    &lt;/description&gt;
  &lt;/property&gt;
  ...
&lt;/configuration&gt;
</pre>
</blockquote>

<p>In fully-distributed mode, you probably want to change your <code>hbase.rootdir</code>
from localhost to the name of the node running the HDFS NameNode and you should set
the dfs.replication to be the number of datanodes you have in your cluster or 3, which
ever is the smaller.
</p>
<p>In addition
to <code>hbase-site.xml</code> changes, a fully-distributed mode requires that you
modify <code>${HBASE_HOME}/conf/regionservers</code>.
The <code>regionserver</code> file lists all hosts running <code>HRegionServer</code>s, one host per line
(This file in HBase is like the Hadoop slaves file at <code>${HADOOP_HOME}/conf/slaves</code>).</p>

<p>A distributed HBase depends on a running ZooKeeper cluster. All participating nodes and clients
need to be able to get to the running ZooKeeper cluster.
HBase by default manages a ZooKeeper cluster for you, or you can manage it on your own and point HBase to it.
To toggle HBase management of ZooKeeper, use the <code>HBASE_MANAGES_ZK</code> variable in <code>${HBASE_HOME}/conf/hbase-env.sh</code>.
This variable, which defaults to <code>true</code>, tells HBase whether to
start/stop the ZooKeeper quorum servers alongside the rest of the servers.</p>

<p>When HBase manages the ZooKeeper cluster, you can specify ZooKeeper configuration
using its canonical <code>zoo.cfg</code> file (see below), or 
just specify ZookKeeper options directly in the <code>${HBASE_HOME}/conf/hbase-site.xml</code>
(If new to ZooKeeper, go the path of specifying your configuration in HBase's hbase-site.xml).
Every ZooKeeper configuration option has a corresponding property in the HBase hbase-site.xml
XML configuration file named <code>hbase.zookeeper.property.OPTION</code>.
For example, the <code>clientPort</code> setting in ZooKeeper can be changed by
setting the <code>hbase.zookeeper.property.clientPort</code> property.
For the full list of available properties, see ZooKeeper's <code>zoo.cfg</code>.
For the default values used by HBase, see <code>${HBASE_HOME}/conf/hbase-default.xml</code>.</p>

<p>At minimum, you should set the list of servers that you want ZooKeeper to run
on using the <code>hbase.zookeeper.quorum</code> property.
This property defaults to <code>localhost</code> which is not suitable for a
fully distributed HBase (it binds to the local machine only and remote clients
will not be able to connect).
It is recommended to run a ZooKeeper quorum of 3, 5 or 7 machines, and give each
ZooKeeper server around 1GB of RAM, and if possible, its own dedicated disk.
For very heavily loaded clusters, run ZooKeeper servers on separate machines from the
Region Servers (DataNodes and TaskTrackers).</p>

<p>To point HBase at an existing ZooKeeper cluster, add 
a suitably configured <code>zoo.cfg</code> to the <code>CLASSPATH</code>.
HBase will see this file and use it to figure out where ZooKeeper is.
Additionally set <code>HBASE_MANAGES_ZK</code> in <code>${HBASE_HOME}/conf/hbase-env.sh</code>
to <code>false</code> so that HBase doesn't mess with your ZooKeeper setup:</p>
<blockquote>
<pre>
   ...
  # Tell HBase whether it should manage it's own instance of Zookeeper or not.
  export HBASE_MANAGES_ZK=false
</pre>
</blockquote>

<p>As an example, to have HBase manage a ZooKeeper quorum on nodes
<em>rs{1,2,3,4,5}.example.com</em>, bound to port 2222 (the default is 2181), use:</p>
<blockquote>
<pre>
  ${HBASE_HOME}/conf/hbase-env.sh:

       ...
      # Tell HBase whether it should manage it's own instance of Zookeeper or not.
      export HBASE_MANAGES_ZK=true

  ${HBASE_HOME}/conf/hbase-site.xml:

  &lt;configuration&gt;
    ...
    &lt;property&gt;
      &lt;name&gt;hbase.zookeeper.property.clientPort&lt;/name&gt;
      &lt;value&gt;2222&lt;/value&gt;
      &lt;description&gt;Property from ZooKeeper's config zoo.cfg.
      The port at which the clients will connect.
      &lt;/description&gt;
    &lt;/property&gt;
    ...
    &lt;property&gt;
      &lt;name&gt;hbase.zookeeper.quorum&lt;/name&gt;
      &lt;value&gt;rs1.example.com,rs2.example.com,rs3.example.com,rs4.example.com,rs5.example.com&lt;/value&gt;
      &lt;description&gt;Comma separated list of servers in the ZooKeeper Quorum.
      For example, "host1.mydomain.com,host2.mydomain.com,host3.mydomain.com".
      By default this is set to localhost for local and pseudo-distributed modes
      of operation. For a fully-distributed setup, this should be set to a full
      list of ZooKeeper quorum servers. If HBASE_MANAGES_ZK is set in hbase-env.sh
      this is the list of servers which we will start/stop ZooKeeper on.
      &lt;/description&gt;
    &lt;/property&gt;
    ...
  &lt;/configuration&gt;
</pre>
</blockquote>

<p>When HBase manages ZooKeeper, it will start/stop the ZooKeeper servers as a part
of the regular start/stop scripts. If you would like to run it yourself, you can
do:</p>
<blockquote>
<pre>${HBASE_HOME}/bin/hbase-daemons.sh {start,stop} zookeeper</pre>
</blockquote>

<p>If you do let HBase manage ZooKeeper for you, make sure you configure
where it's data is stored. By default, it will be stored in /tmp which is
sometimes cleaned in live systems. Do modify this configuration:</p>
<pre>
    &lt;property&gt;
      &lt;name&gt;hbase.zookeeper.property.dataDir&lt;/name&gt;
      &lt;value&gt;${hbase.tmp.dir}/zookeeper&lt;/value&gt;
      &lt;description>Property from ZooKeeper's config zoo.cfg.
      The directory where the snapshot is stored.
      &lt;/description&gt;
    &lt;/property&gt;

</pre>

<p>Note that you can use HBase in this manner to spin up a ZooKeeper cluster,
unrelated to HBase. Just make sure to set <code>HBASE_MANAGES_ZK</code> to
<code>false</code> if you want it to stay up so that when HBase shuts down it
doesn't take ZooKeeper with it.</p>

<p>For more information about setting up a ZooKeeper cluster on your own, see
the ZooKeeper <a href="http://hadoop.apache.org/zookeeper/docs/current/zookeeperStarted.html">Getting Started Guide</a>.
HBase currently uses ZooKeeper version 3.3.1, so any cluster setup with a
3.x.x version of ZooKeeper should work.</p>

<p>Of note, if you have made <em>HDFS client configuration</em> on your Hadoop cluster, HBase will not
see this configuration unless you do one of the following:</p>
<ul>
  <li>Add a pointer to your <code>HADOOP_CONF_DIR</code> to <code>CLASSPATH</code> in <code>hbase-env.sh</code>.</li>
  <li>Add a copy of <code>hdfs-site.xml</code> (or <code>hadoop-site.xml</code>) to <code>${HBASE_HOME}/conf</code>, or</li>
  <li>if only a small set of HDFS client configurations, add them to <code>hbase-site.xml</code>.</li>
</ul>

<p>An example of such an HDFS client configuration is <code>dfs.replication</code>. If for example,
you want to run with a replication factor of 5, hbase will create files with the default of 3 unless
you do the above to make the configuration available to HBase.</p>


<h2><a name="runandconfirm">Running and Confirming Your Installation</a></h2>
<p>If you are running in standalone, non-distributed mode, HBase by default uses the local filesystem.</p>

<p>If you are running a distributed cluster you will need to start the Hadoop DFS daemons and
ZooKeeper Quorum before starting HBase and stop the daemons after HBase has shut down.</p>

<p>Start and stop the Hadoop DFS daemons by running <code>${HADOOP_HOME}/bin/start-dfs.sh</code>.
You can ensure it started properly by testing the put and get of files into the Hadoop filesystem.
HBase does not normally use the mapreduce daemons.  These do not need to be started.</p>

<p>Start up your ZooKeeper cluster.</p>

<p>Start HBase with the following command:</p>
<blockquote>
<pre>${HBASE_HOME}/bin/start-hbase.sh</pre>
</blockquote>

<p>Once HBase has started, enter <code>${HBASE_HOME}/bin/hbase shell</code> to obtain a
shell against HBase from which you can execute commands.
Type 'help' at the shells' prompt to get a list of commands.
Test your running install by creating tables, inserting content, viewing content, and then dropping your tables.
For example:</p>
<blockquote>
<pre>
hbase&gt; # Type "help" to see shell help screen
hbase&gt; help
hbase&gt; # To create a table named "mylittletable" with a column family of "mylittlecolumnfamily", type
hbase&gt; create "mylittletable", "mylittlecolumnfamily"
hbase&gt; # To see the schema for you just created "mylittletable" table and its single "mylittlecolumnfamily", type
hbase&gt; describe "mylittletable"
hbase&gt; # To add a row whose id is "myrow", to the column "mylittlecolumnfamily:x" with a value of 'v', do
hbase&gt; put "mylittletable", "myrow", "mylittlecolumnfamily:x", "v"
hbase&gt; # To get the cell just added, do
hbase&gt; get "mylittletable", "myrow"
hbase&gt; # To scan you new table, do
hbase&gt; scan "mylittletable"
</pre>
</blockquote>

<p>To stop HBase, exit the HBase shell and enter:</p>
<blockquote>
<pre>${HBASE_HOME}/bin/stop-hbase.sh</pre>
</blockquote>

<p>If you are running a distributed operation, be sure to wait until HBase has shut down completely
before stopping the Hadoop daemons.</p>

<p>The default location for logs is <code>${HBASE_HOME}/logs</code>.</p>

<p>HBase also puts up a UI listing vital attributes. By default its deployed on the master host
at port 60010 (HBase RegionServers listen on port 60020 by default and put up an informational
http server at 60030).</p>

<h2><a name="upgrading" >Upgrading</a></h2>
<p>After installing a new HBase on top of data written by a previous HBase version, before
starting your cluster, run the <code>${HBASE_DIR}/bin/hbase migrate</code> migration script.
It will make any adjustments to the filesystem data under <code>hbase.rootdir</code> necessary to run
the HBase version. It does not change your install unless you explicitly ask it to.</p>

<h2><a name="client_example">Example API Usage</a></h2>
<p>For sample Java code, see <a href="org/apache/hadoop/hbase/client/package-summary.html#package_description">org.apache.hadoop.hbase.client</a> documentation.</p>

<p>If your client is NOT Java, consider the Thrift or REST libraries.</p>

<h2><a name="related" >Related Documentation</a></h2>
<ul>
  <li><a href="http://hbase.org">HBase Home Page</a>
  </li>
  <li><a href="http://wiki.apache.org/hadoop/Hbase">HBase Wiki</a>
  </li>
  <li><a href="http://hadoop.apache.org/">Hadoop Home Page</a>
  </li>
  <li><a href="http://wiki.apache.org/hadoop/Hbase/MultipleMasters">Setting up Multiple HBase Masters</a>
  </li>
  <li><a href="http://wiki.apache.org/hadoop/Hbase/RollingRestart">Rolling Upgrades</a>
  </li>
  <li><a href="org/apache/hadoop/hbase/client/transactional/package-summary.html#package_description">Transactional HBase</a>
  </li>
  <li><a href="org/apache/hadoop/hbase/client/tableindexed/package-summary.html">Table Indexed HBase</a>
  </li>
  <li><a href="org/apache/hadoop/hbase/stargate/package-summary.html#package_description">Stargate</a> -- a RESTful Web service front end for HBase.
  </li>
</ul>

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