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Posted to commits@accumulo.apache.org by bi...@apache.org on 2013/05/25 04:56:12 UTC
svn commit: r1486280 [2/4] - in /accumulo/site/trunk/content: 1.5/
1.5/apidocs/ 1.5/apidocs/org/ 1.5/apidocs/org/apache/
1.5/apidocs/org/apache/accumulo/ 1.5/apidocs/org/apache/accumulo/core/
1.5/apidocs/org/apache/accumulo/core/bloomfilter/ 1.5/apidoc...
Added: accumulo/site/trunk/content/1.5/accumulo_user_manual.html
URL: http://svn.apache.org/viewvc/accumulo/site/trunk/content/1.5/accumulo_user_manual.html?rev=1486280&view=auto
==============================================================================
--- accumulo/site/trunk/content/1.5/accumulo_user_manual.html (added)
+++ accumulo/site/trunk/content/1.5/accumulo_user_manual.html Sat May 25 02:56:08 2013
@@ -0,0 +1,6665 @@
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+<body class="book" style="max-width:50em">
+
+<div id="header">
+
+<h1>Apache Accumulo User Manual Version 1.5</h1>
+
+<span id="author">Apache Accumulo Project</span><br />
+
+<span id="email"><code><<a href="mailto:dev@accumulo.apache.org">dev@accumulo.apache.org</a>></code></span><br />
+
+<div id="toc">
+ <div id="toctitle">Apache Accumulo 1.5</div>
+ <noscript><p><b>JavaScript must be enabled in your browser to display the table of contents.</b></p></noscript>
+</div>
+
+</div>
+
+<div id="content">
+
+<div id="preamble">
+
+<div class="sectionbody">
+
+<div class="imageblock">
+
+<div class="content">
+
+<img src="images/accumulo-logo.png" alt="images/accumulo-logo.png" />
+
+</div>
+
+</div>
+
+<div class="paragraph"><p>Copyright © 2011-2013 The Apache Software Foundation, Licensed under the Apache
+
+License, Version 2.0. Apache Accumulo, Accumulo, Apache, and the Apache
+
+Accumulo project logo are trademarks of the Apache Software Foundation.</p></div>
+
+</div>
+
+</div>
+
+<div class="sect1">
+
+<h2 id="_introduction">1. Introduction</h2>
+
+<div class="sectionbody">
+
+<div class="paragraph"><p>Apache Accumulo is a highly scalable structured store based on Google’s BigTable.
+
+Accumulo is written in Java and operates over the Hadoop Distributed File System
+
+(HDFS), which is part of the popular Apache Hadoop project. Accumulo supports
+
+efficient storage and retrieval of structured data, including queries for ranges, and
+
+provides support for using Accumulo tables as input and output for MapReduce
+
+jobs.</p></div>
+
+<div class="paragraph"><p>Accumulo features automatic load-balancing and partitioning, data compression
+
+and fine-grained security labels.</p></div>
+
+</div>
+
+</div>
+
+<div class="sect1">
+
+<h2 id="_accumulo_design">2. Accumulo Design</h2>
+
+<div class="sectionbody">
+
+<div class="sect2">
+
+<h3 id="_data_model">2.1. Data Model</h3>
+
+<div class="paragraph"><p>Accumulo provides a richer data model than simple key-value stores, but is not a
+
+fully relational database. Data is represented as key-value pairs, where the key and
+
+value are comprised of the following elements:</p></div>
+
+<div class="tableblock">
+
+<table rules="all"
+
+width="75%"
+
+frame="border"
+
+cellspacing="0" cellpadding="4">
+
+<col width="16%" />
+
+<col width="16%" />
+
+<col width="16%" />
+
+<col width="16%" />
+
+<col width="16%" />
+
+<col width="16%" />
+
+<tbody>
+
+<tr>
+
+<td colspan="5" align="center" valign="top"><p class="table">Key</p></td>
+
+<td rowspan="3" align="center" valign="middle"><p class="table">Value</p></td>
+
+</tr>
+
+<tr>
+
+<td rowspan="2" align="center" valign="middle"><p class="table">Row ID</p></td>
+
+<td colspan="3" align="center" valign="top"><p class="table">Column</p></td>
+
+<td rowspan="2" align="center" valign="middle"><p class="table">Timestamp</p></td>
+
+</tr>
+
+<tr>
+
+<td align="center" valign="top"><p class="table">Family</p></td>
+
+<td align="center" valign="top"><p class="table">Qualifier</p></td>
+
+<td align="center" valign="top"><p class="table">Visibility</p></td>
+
+</tr>
+
+</tbody>
+
+</table>
+
+</div>
+
+<div class="paragraph"><p>All elements of the Key and the Value are represented as byte arrays except for
+
+Timestamp, which is a Long. Accumulo sorts keys by element and lexicographically
+
+in ascending order. Timestamps are sorted in descending order so that later
+
+versions of the same Key appear first in a sequential scan. Tables consist of a set of
+
+sorted key-value pairs.</p></div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_architecture">2.2. Architecture</h3>
+
+<div class="paragraph"><p>Accumulo is a distributed data storage and retrieval system and as such consists of
+
+several architectural components, some of which run on many individual servers.
+
+Much of the work Accumulo does involves maintaining certain properties of the
+
+data, such as organization, availability, and integrity, across many commodity-class
+
+machines.</p></div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_components">2.3. Components</h3>
+
+<div class="paragraph"><p>An instance of Accumulo includes many TabletServers, one Garbage Collector process,
+
+one Master server and many Clients.</p></div>
+
+<div class="sect3">
+
+<h4 id="_tablet_server">2.3.1. Tablet Server</h4>
+
+<div class="paragraph"><p>The TabletServer manages some subset of all the tablets (partitions of tables).
+
+This includes receiving writes from clients, persisting writes to a
+
+write-ahead log, sorting new key-value pairs in memory, periodically
+
+flushing sorted key-value pairs to new files in HDFS, and responding
+
+to reads from clients, forming a merge-sorted view of all keys and
+
+values from all the files it has created and the sorted in-memory
+
+store.</p></div>
+
+<div class="paragraph"><p>TabletServers also perform recovery of a tablet
+
+that was previously on a server that failed, reapplying any writes
+
+found in the write-ahead log to the tablet.</p></div>
+
+</div>
+
+<div class="sect3">
+
+<h4 id="_garbage_collector">2.3.2. Garbage Collector</h4>
+
+<div class="paragraph"><p>Accumulo processes will share files stored in HDFS. Periodically, the Garbage
+
+Collector will identify files that are no longer needed by any process, and
+
+delete them.</p></div>
+
+</div>
+
+<div class="sect3">
+
+<h4 id="_master">2.3.3. Master</h4>
+
+<div class="paragraph"><p>The Accumulo Master is responsible for detecting and responding to TabletServer
+
+failure. It tries to balance the load across TabletServer by assigning tablets carefully
+
+and instructing TabletServers to unload tablets when necessary. The Master ensures all
+
+tablets are assigned to one TabletServer each, and handles table creation, alteration,
+
+and deletion requests from clients. The Master also coordinates startup, graceful
+
+shutdown and recovery of changes in write-ahead logs when Tablet servers fail.</p></div>
+
+<div class="paragraph"><p>Multiple masters may be run. The masters will choose among themselves a single master,
+
+and the others will become backups if the master should fail.</p></div>
+
+</div>
+
+<div class="sect3">
+
+<h4 id="_client">2.3.4. Client</h4>
+
+<div class="paragraph"><p>Accumulo includes a client library that is linked to every application. The client
+
+library contains logic for finding servers managing a particular tablet, and
+
+communicating with TabletServers to write and retrieve key-value pairs.</p></div>
+
+</div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_data_management">2.4. Data Management</h3>
+
+<div class="paragraph"><p>Accumulo stores data in tables, which are partitioned into tablets. Tablets are
+
+partitioned on row boundaries so that all of the columns and values for a particular
+
+row are found together within the same tablet. The Master assigns Tablets to one
+
+TabletServer at a time. This enables row-level transactions to take place without
+
+using distributed locking or some other complicated synchronization mechanism. As
+
+clients insert and query data, and as machines are added and removed from the
+
+cluster, the Master migrates tablets to ensure they remain available and that the
+
+ingest and query load is balanced across the cluster.</p></div>
+
+<div class="imageblock">
+
+<div class="content">
+
+<img src="images/data_distribution.png" alt="images/data_distribution.png" width="500" />
+
+</div>
+
+</div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_tablet_service">2.5. Tablet Service</h3>
+
+<div class="paragraph"><p>When a write arrives at a TabletServer it is written to a Write-Ahead Log and
+
+then inserted into a sorted data structure in memory called a MemTable. When the
+
+MemTable reaches a certain size the TabletServer writes out the sorted key-value
+
+pairs to a file in HDFS called Indexed Sequential Access Method (ISAM)
+
+file. This process is called a minor compaction. A new MemTable is then created
+
+and the fact of the compaction is recorded in the Write-Ahead Log.</p></div>
+
+<div class="paragraph"><p>When a request to read data arrives at a TabletServer, the TabletServer does a
+
+binary search across the MemTable as well as the in-memory indexes associated
+
+with each ISAM file to find the relevant values. If clients are performing a
+
+scan, several key-value pairs are returned to the client in order from the
+
+MemTable and the set of ISAM files by performing a merge-sort as they are read.</p></div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_compactions">2.6. Compactions</h3>
+
+<div class="paragraph"><p>In order to manage the number of files per tablet, periodically the TabletServer
+
+performs Major Compactions of files within a tablet, in which some set of ISAM
+
+files are combined into one file. The previous files will eventually be removed
+
+by the Garbage Collector. This also provides an opportunity to permanently
+
+remove deleted key-value pairs by omitting key-value pairs suppressed by a
+
+delete entry when the new file is created.</p></div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_splitting">2.7. Splitting</h3>
+
+<div class="paragraph"><p>When a table is created it has one tablet. As the table grows its initial
+
+tablet eventually splits into two tablets. Its likely that one of these
+
+tablets will migrate to another tablet server. As the table continues to grow,
+
+its tablets will continue to split and be migrated. The decision to
+
+automatically split a tablet is based on the size of a tablets files. The
+
+size threshold at which a tablet splits is configurable per table. In addition
+
+to automatic splitting, a user can manually add split points to a table to
+
+create new tablets. Manually splitting a new table can parallelize reads and
+
+writes giving better initial performance without waiting for automatic
+
+splitting.</p></div>
+
+<div class="paragraph"><p>As data is deleted from a table, tablets may shrink. Over time this can lead
+
+to small or empty tablets. To deal with this, merging of tablets was
+
+introduced in Accumulo 1.4. This is discussed in more detail later.</p></div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_fault_tolerance">2.8. Fault-Tolerance</h3>
+
+<div class="paragraph"><p>If a TabletServer fails, the Master detects it and automatically reassigns the tablets
+
+assigned from the failed server to other servers. Any key-value pairs that were in
+
+memory at the time the TabletServer fails are automatically reapplied from the Write-Ahead
+
+Log to prevent any loss of data.</p></div>
+
+<div class="paragraph"><p>The Master will coordinate the copying of write-ahead logs to HDFS so the logs
+
+are available to all tablet servers. To make recovery efficient, the updates
+
+within a log are grouped by tablet. TabletServers can quickly apply the
+
+mutations from the sorted logs that are destined for the tablets they have now
+
+been assigned.</p></div>
+
+<div class="paragraph"><p>TabletServer failures are noted on the Master’s monitor page, accessible via
+
+<code>http://master-address:50095/monitor</code>.</p></div>
+
+<div class="imageblock">
+
+<div class="content">
+
+<img src="images/failure_handling.png" alt="images/failure_handling.png" width="500" />
+
+</div>
+
+</div>
+
+</div>
+
+</div>
+
+</div>
+
+<div class="sect1">
+
+<h2 id="_accumulo_shell">3. Accumulo Shell</h2>
+
+<div class="sectionbody">
+
+<div class="paragraph"><p>Accumulo provides a simple shell that can be used to examine the contents and
+
+configuration settings of tables, insert/update/delete values, and change
+
+configuration settings.</p></div>
+
+<div class="paragraph"><p>The shell can be started by the following command:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>$ACCUMULO_HOME/bin/accumulo shell -u [username]</code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>The shell will prompt for the corresponding password to the username specified
+
+and then display the following prompt:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>Shell - Apache Accumulo Interactive Shell
+
+-
+
+- version 1.5
+
+- instance name: myinstance
+
+- instance id: 00000000-0000-0000-0000-000000000000
+
+-
+
+- type 'help' for a list of available commands
+
+-</code></pre>
+
+</div></div>
+
+<div class="sect2">
+
+<h3 id="_basic_administration">3.1. Basic Administration</h3>
+
+<div class="paragraph"><p>The Accumulo shell can be used to create and delete tables, as well as to configure
+
+table and instance specific options.</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance> tables
+
+!METADATA</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance> createtable mytable</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance mytable></code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance mytable> tables
+
+!METADATA
+
+mytable</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance mytable> createtable testtable</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance testtable></code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance testtable> deletetable testtable</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance></code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>The Shell can also be used to insert updates and scan tables. This is useful for
+
+inspecting tables.</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance mytable> scan</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance mytable> insert row1 colf colq value1
+
+insert successful</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance mytable> scan
+
+row1 colf:colq [] value1</code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>The value in brackets “[]” would be the visibility labels. Since none were used, this is empty for this row.
+
+You can use the “-st” option to scan to see the timestamp for the cell, too.</p></div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_table_maintenance">3.2. Table Maintenance</h3>
+
+<div class="paragraph"><p>The <strong>compact</strong> command instructs Accumulo to schedule a compaction of the table during which
+
+files are consolidated and deleted entries are removed.</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance mytable> compact -t mytable
+
+07 16:13:53,201 [shell.Shell] INFO : Compaction of table mytable
+
+scheduled for 20100707161353EDT</code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>The <strong>flush</strong> command instructs Accumulo to write all entries currently in memory for a given table
+
+to disk.</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance mytable> flush -t mytable
+
+07 16:14:19,351 [shell.Shell] INFO : Flush of table mytable
+
+initiated...</code></pre>
+
+</div></div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_user_administration">3.3. User Administration</h3>
+
+<div class="paragraph"><p>The Shell can be used to add, remove, and grant privileges to users.</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance mytable> createuser bob
+
+Enter new password for 'bob': *********
+
+Please confirm new password for 'bob': *********</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance mytable> authenticate bob
+
+Enter current password for 'bob': *********
+
+Valid</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance mytable> grant System.CREATE_TABLE -s -u bob</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance mytable> user bob
+
+Enter current password for 'bob': *********</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>bob@myinstance mytable> userpermissions
+
+System permissions: System.CREATE_TABLE
+
+Table permissions (!METADATA): Table.READ
+
+Table permissions (mytable): NONE</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>bob@myinstance mytable> createtable bobstable
+
+bob@myinstance bobstable></code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>bob@myinstance bobstable> user root
+
+Enter current password for 'root': *********</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@myinstance bobstable> revoke System.CREATE_TABLE -s -u bob</code></pre>
+
+</div></div>
+
+</div>
+
+</div>
+
+</div>
+
+<div class="sect1">
+
+<h2 id="_writing_accumulo_clients">4. Writing Accumulo Clients</h2>
+
+<div class="sectionbody">
+
+<div class="sect2">
+
+<h3 id="_running_client_code">4.1. Running Client Code</h3>
+
+<div class="paragraph"><p>There are multiple ways to run Java code that uses Accumulo. Below is a list
+
+of the different ways to execute client code.</p></div>
+
+<div class="ulist"><ul>
+
+<li>
+
+<p>
+
+using java executable
+
+</p>
+
+</li>
+
+<li>
+
+<p>
+
+using the accumulo script
+
+</p>
+
+</li>
+
+<li>
+
+<p>
+
+using the tool script
+
+</p>
+
+</li>
+
+</ul></div>
+
+<div class="paragraph"><p>In order to run client code written to run against Accumulo, you will need to
+
+include the jars that Accumulo depends on in your classpath. Accumulo client
+
+code depends on Hadoop and Zookeeper. For Hadoop add the hadoop core jar, all
+
+of the jars in the Hadoop lib directory, and the conf directory to the
+
+classpath. For Zookeeper 3.3 you only need to add the Zookeeper jar, and not
+
+what is in the Zookeeper lib directory. You can run the following command on a
+
+configured Accumulo system to see what its using for its classpath.</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>$ACCUMULO_HOME/bin/accumulo classpath</code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>Another option for running your code is to put a jar file in
+
+<code>$ACCUMULO_HOME/lib/ext</code>. After doing this you can use the accumulo
+
+script to execute your code. For example if you create a jar containing the
+
+class com.foo.Client and placed that in <code>lib/ext</code>, then you could use the command
+
+<code>$ACCUMULO_HOME/bin/accumulo com.foo.Client</code> to execute your code.</p></div>
+
+<div class="paragraph"><p>If you are writing map reduce job that access Accumulo, then you can use the
+
+bin/tool.sh script to run those jobs. See the map reduce example.</p></div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_connecting">4.2. Connecting</h3>
+
+<div class="paragraph"><p>All clients must first identify the Accumulo instance to which they will be
+
+communicating. Code to do this is as follows:</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt><span style="color: #000000">String</span> instanceName = <span style="color: #4c73a6">"myinstance"</span>;
+
+<span style="color: #000000">String</span> zooServers = <span style="color: #4c73a6">"zooserver-one,zooserver-two"</span>
+
+<span style="color: #000000">Instance</span> inst = <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">ZooKeeperInstance</span></span>(instanceName, zooServers);
+
+<span style="color: #000000">Connector</span> conn = inst.<span style="font-weight: bold"><span style="color: #000000">getConnector</span></span>(<span style="color: #4c73a6">"user"</span>, <span style="color: #4c73a6">"passwd"</span>);</tt></pre></div></div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_writing_data">4.3. Writing Data</h3>
+
+<div class="paragraph"><p>Data are written to Accumulo by creating Mutation objects that represent all the
+
+changes to the columns of a single row. The changes are made atomically in the
+
+TabletServer. Clients then add Mutations to a BatchWriter which submits them to
+
+the appropriate TabletServers.</p></div>
+
+<div class="paragraph"><p>Mutations can be created thus:</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt><span style="color: #000000">Text</span> rowID = <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">Text</span></span>(<span style="color: #4c73a6">"row1"</span>);
+
+<span style="color: #000000">Text</span> colFam = <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">Text</span></span>(<span style="color: #4c73a6">"myColFam"</span>);
+
+<span style="color: #000000">Text</span> colQual = <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">Text</span></span>(<span style="color: #4c73a6">"myColQual"</span>);
+
+<span style="color: #000000">ColumnVisibility</span> colVis = <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">ColumnVisibility</span></span>(<span style="color: #4c73a6">"public"</span>);
+
+<span style="color: #000000">long</span> timestamp = System.<span style="font-weight: bold"><span style="color: #000000">currentTimeMillis</span></span>();
+
+
+
+<span style="color: #000000">Value</span> value = <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">Value</span></span>(<span style="color: #4c73a6">"myValue"</span>.<span style="font-weight: bold"><span style="color: #000000">getBytes</span></span>());
+
+
+
+<span style="color: #000000">Mutation</span> mutation = <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">Mutation</span></span>(rowID);
+
+mutation.<span style="font-weight: bold"><span style="color: #000000">put</span></span>(colFam, colQual, colVis, timestamp, value);</tt></pre></div></div>
+
+<div class="sect3">
+
+<h4 id="_batchwriter">4.3.1. BatchWriter</h4>
+
+<div class="paragraph"><p>The BatchWriter is highly optimized to send Mutations to multiple TabletServers
+
+and automatically batches Mutations destined for the same TabletServer to
+
+amortize network overhead. Care must be taken to avoid changing the contents of
+
+any Object passed to the BatchWriter since it keeps objects in memory while
+
+batching.</p></div>
+
+<div class="paragraph"><p>Mutations are added to a BatchWriter thus:</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt><span style="color: #000000">long</span> memBuf = <span style="color: #000000">1000000L</span>; <span style="font-style: italic"><span style="color: #b30000">// bytes to store before sending a batch</span></span>
+
+<span style="color: #000000">long</span> timeout = <span style="color: #000000">1000L</span>; <span style="font-style: italic"><span style="color: #b30000">// milliseconds to wait before sending</span></span>
+
+<span style="color: #000000">int</span> numThreads = <span style="color: #000000">10</span>;
+
+
+
+<span style="color: #000000">BatchWriter</span> writer =
+
+ conn.<span style="font-weight: bold"><span style="color: #000000">createBatchWriter</span></span>(<span style="color: #4c73a6">"table"</span>, memBuf, timeout, numThreads)
+
+
+
+writer.<span style="font-weight: bold"><span style="color: #000000">add</span></span>(mutation);
+
+
+
+writer.<span style="font-weight: bold"><span style="color: #000000">close</span></span>();</tt></pre></div></div>
+
+<div class="paragraph"><p>An example of using the batch writer can be found at
+
+<code>accumulo/docs/examples/README.batch</code></p></div>
+
+</div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_reading_data">4.4. Reading Data</h3>
+
+<div class="paragraph"><p>Accumulo is optimized to quickly retrieve the value associated with a given key, and
+
+to efficiently return ranges of consecutive keys and their associated values.</p></div>
+
+<div class="sect3">
+
+<h4 id="_scanner">4.4.1. Scanner</h4>
+
+<div class="paragraph"><p>To retrieve data, Clients use a Scanner, which acts like an Iterator over
+
+keys and values. Scanners can be configured to start and stop at particular keys, and
+
+to return a subset of the columns available.</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt><span style="font-style: italic"><span style="color: #b30000">// specify which visibilities we are allowed to see</span></span>
+
+<span style="color: #000000">Authorizations</span> auths = <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">Authorizations</span></span>(<span style="color: #4c73a6">"public"</span>);
+
+
+
+<span style="color: #000000">Scanner</span> scan =
+
+ conn.<span style="font-weight: bold"><span style="color: #000000">createScanner</span></span>(<span style="color: #4c73a6">"table"</span>, auths);
+
+
+
+scan.<span style="font-weight: bold"><span style="color: #000000">setRange</span></span>(<span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">Range</span></span>(<span style="color: #4c73a6">"harry"</span>,<span style="color: #4c73a6">"john"</span>));
+
+scan.<span style="font-weight: bold"><span style="color: #000000">fetchFamily</span></span>(<span style="color: #4c73a6">"attributes"</span>);
+
+
+
+<span style="color: #0000b3">for</span>(<span style="color: #000000">Entry<Key,Value></span> entry : scan) {
+
+ <span style="color: #000000">String</span> row = entry.<span style="font-weight: bold"><span style="color: #000000">getKey</span></span>().<span style="font-weight: bold"><span style="color: #000000">getRow</span></span>();
+
+ <span style="color: #000000">Value</span> value = entry.<span style="font-weight: bold"><span style="color: #000000">getValue</span></span>();
+
+}</tt></pre></div></div>
+
+</div>
+
+<div class="sect3">
+
+<h4 id="_isolated_scanner">4.4.2. Isolated Scanner</h4>
+
+<div class="paragraph"><p>Accumulo supports the ability to present an isolated view of rows when
+
+scanning. There are three possible ways that a row could change in accumulo:</p></div>
+
+<div class="ulist"><ul>
+
+<li>
+
+<p>
+
+a mutation applied to a table
+
+</p>
+
+</li>
+
+<li>
+
+<p>
+
+iterators executed as part of a minor or major compaction
+
+</p>
+
+</li>
+
+<li>
+
+<p>
+
+bulk import of new files
+
+</p>
+
+</li>
+
+</ul></div>
+
+<div class="paragraph"><p>Isolation guarantees that either all or none of the changes made by these
+
+operations on a row are seen. Use the IsolatedScanner to obtain an isolated
+
+view of an accumulo table. When using the regular scanner it is possible to see
+
+a non isolated view of a row. For example if a mutation modifies three
+
+columns, it is possible that you will only see two of those modifications.
+
+With the isolated scanner either all three of the changes are seen or none.</p></div>
+
+<div class="paragraph"><p>The IsolatedScanner buffers rows on the client side so a large row will not
+
+crash a tablet server. By default rows are buffered in memory, but the user
+
+can easily supply their own buffer if they wish to buffer to disk when rows are
+
+large.</p></div>
+
+<div class="paragraph"><p>For an example, look at the following
+
+<code>examples/simple/src/main/java/org/apache/accumulo/examples/simple/isolation/InterferenceTest.java</code></p></div>
+
+</div>
+
+<div class="sect3">
+
+<h4 id="_batchscanner">4.4.3. BatchScanner</h4>
+
+<div class="paragraph"><p>For some types of access, it is more efficient to retrieve several ranges
+
+simultaneously. This arises when accessing a set of rows that are not consecutive
+
+whose IDs have been retrieved from a secondary index, for example.</p></div>
+
+<div class="paragraph"><p>The BatchScanner is configured similarly to the Scanner; it can be configured to
+
+retrieve a subset of the columns available, but rather than passing a single Range,
+
+BatchScanners accept a set of Ranges. It is important to note that the keys returned
+
+by a BatchScanner are not in sorted order since the keys streamed are from multiple
+
+TabletServers in parallel.</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt><span style="color: #000000">ArrayList<Range></span> ranges = <span style="color: #0000b3">new</span> ArrayList<Range>();
+
+<span style="font-style: italic"><span style="color: #b30000">// populate list of ranges ...</span></span>
+
+
+
+<span style="color: #000000">BatchScanner</span> bscan =
+
+ conn.<span style="font-weight: bold"><span style="color: #000000">createBatchScanner</span></span>(<span style="color: #4c73a6">"table"</span>, auths, <span style="color: #000000">10</span>);
+
+
+
+bscan.<span style="font-weight: bold"><span style="color: #000000">setRanges</span></span>(ranges);
+
+bscan.<span style="font-weight: bold"><span style="color: #000000">fetchFamily</span></span>(<span style="color: #4c73a6">"attributes"</span>);
+
+
+
+<span style="color: #0000b3">for</span>(<span style="color: #000000">Entry<Key,Value></span> entry : scan)
+
+ System.out.<span style="font-weight: bold"><span style="color: #000000">println</span></span>(entry.<span style="font-weight: bold"><span style="color: #000000">getValue</span></span>());</tt></pre></div></div>
+
+<div class="paragraph"><p>An example of the BatchScanner can be found at
+
+<code>accumulo/docs/examples/README.batch</code></p></div>
+
+</div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_proxy">4.5. Proxy</h3>
+
+<div class="paragraph"><p>The proxy API allows the interaction with Accumulo with languages other than Java.
+
+A proxy server is provided in the codebase and a client can further be generated.</p></div>
+
+<div class="sect3">
+
+<h4 id="_prequisites">4.5.1. Prequisites</h4>
+
+<div class="paragraph"><p>The proxy server can live on any node in which the basic client API would work. That
+
+means it must be able to communicate with the Master, ZooKeepers, NameNode, and the
+
+Data nodes. A proxy client only needs the ability to communicate with the proxy server.</p></div>
+
+</div>
+
+<div class="sect3">
+
+<h4 id="_configuration">4.5.2. Configuration</h4>
+
+<div class="paragraph"><p>The configuration options for the proxy server live inside of a properties file. At
+
+the very least, you need to supply the following properties:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>protocolFactory=org.apache.thrift.protocol.TCompactProtocol$Factory
+
+tokenClass=org.apache.accumulo.core.client.security.tokens.PasswordToken
+
+port=42424
+
+instance=test
+
+zookeepers=localhost:2181</code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>You can find a sample configuration file in your distribution:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>$ACCUMULO_HOME/proxy/proxy.properties</code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>This sample configuration file further demonstrates an abilty to back the proxy server
+
+by MockAccumulo or the MiniAccumuloCluster.</p></div>
+
+</div>
+
+<div class="sect3">
+
+<h4 id="_running_the_proxy_server">4.5.3. Running the Proxy Server</h4>
+
+<div class="paragraph"><p>After the properties file holding the configuration is created, the proxy server
+
+can be started using the following command in the Accumulo distribution (assuming
+
+you your properties file is named config.properties):</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>$ACCUMULO_HOME/bin/accumulo proxy -p config.properties</code></pre>
+
+</div></div>
+
+</div>
+
+<div class="sect3">
+
+<h4 id="_creating_a_proxy_client">4.5.4. Creating a Proxy Client</h4>
+
+<div class="paragraph"><p>Aside from installing the Thrift compiler, you will also need the language-specific library
+
+for Thrift installed to generate client code in that language. Typically, your operating
+
+system’s package manager will be able to automatically install these for you in an expected
+
+location such as /usr/lib/python/site-packages/thrift.</p></div>
+
+<div class="paragraph"><p>You can find the thrift file for generating the client:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>$ACCUMULO_HOME/proxy/proxy.thrift</code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>After a client is generated, the port specified in the configuration properties above will be
+
+used to connect to the server.</p></div>
+
+</div>
+
+<div class="sect3">
+
+<h4 id="_using_a_proxy_client">4.5.5. Using a Proxy Client</h4>
+
+<div class="paragraph"><p>The following examples have been written in Java and the method signatures may be
+
+slightly different depending on the language specified when generating client with
+
+the Thrift compiler. After initiating a connection to the Proxy (see Apache Thrift’s
+
+documentation for examples of connecting to a Thrift service), the methods on the
+
+proxy client will be available. The first thing to do is log in:</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt><span style="color: #000000">Map</span> password = <span style="color: #0000b3">new</span> HashMap<String,String>();
+
+password.<span style="font-weight: bold"><span style="color: #000000">put</span></span>(<span style="color: #4c73a6">"password"</span>, <span style="color: #4c73a6">"secret"</span>);
+
+<span style="color: #000000">ByteBuffer</span> token = client.<span style="font-weight: bold"><span style="color: #000000">login</span></span>(<span style="color: #4c73a6">"root"</span>, password);</tt></pre></div></div>
+
+<div class="paragraph"><p>Once logged in, the token returned will be used for most subsequent calls to the client.
+
+Let’s create a table, add some data, scan the table, and delete it.</p></div>
+
+<div class="paragraph"><p>First, create a table.</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt>client.<span style="font-weight: bold"><span style="color: #000000">createTable</span></span>(token, <span style="color: #4c73a6">"myTable"</span>, <span style="color: #0000b3">true</span>, TimeType.MILLIS);</tt></pre></div></div>
+
+<div class="paragraph"><p>Next, add some data:</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt><span style="font-style: italic"><span style="color: #b30000">// first, create a writer on the server</span></span>
+
+<span style="color: #000000">String</span> writer = client.<span style="font-weight: bold"><span style="color: #000000">createWriter</span></span>(token, <span style="color: #4c73a6">"myTable"</span>, <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">WriterOptions</span></span>());
+
+
+
+<span style="font-style: italic"><span style="color: #b30000">// build column updates</span></span>
+
+<span style="color: #000000">Map<ByteBuffer, List<ColumnUpdate> cells></span> cellsToUpdate = <span style="font-style: italic"><span style="color: #b30000">//...</span></span>
+
+
+
+<span style="font-style: italic"><span style="color: #b30000">// send updates to the server</span></span>
+
+client.<span style="font-weight: bold"><span style="color: #000000">updateAndFlush</span></span>(writer, <span style="color: #4c73a6">"myTable"</span>, cellsToUpdate);
+
+
+
+client.<span style="font-weight: bold"><span style="color: #000000">closeWriter</span></span>(writer);</tt></pre></div></div>
+
+<div class="paragraph"><p>Scan for the data and batch the return of the results on the server:</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt><span style="color: #000000">String</span> scanner = client.<span style="font-weight: bold"><span style="color: #000000">createScanner</span></span>(token, <span style="color: #4c73a6">"myTable"</span>, <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">ScanOptions</span></span>());
+
+<span style="color: #000000">ScanResult</span> results = client.<span style="font-weight: bold"><span style="color: #000000">nextK</span></span>(scanner, <span style="color: #000000">100</span>);
+
+
+
+<span style="color: #0000b3">for</span>(<span style="color: #000000">KeyValue</span> keyValue : results.<span style="font-weight: bold"><span style="color: #000000">getResultsIterator</span></span>()) {
+
+ <span style="font-style: italic"><span style="color: #b30000">// do something with results</span></span>
+
+}
+
+
+
+client.<span style="font-weight: bold"><span style="color: #000000">closeScanner</span></span>(scanner);</tt></pre></div></div>
+
+</div>
+
+</div>
+
+</div>
+
+</div>
+
+<div class="sect1">
+
+<h2 id="_development_clients">5. Development Clients</h2>
+
+<div class="sectionbody">
+
+<div class="paragraph"><p>Normally, Accumulo consists of lots of moving parts. Even a stand-alone version of
+
+Accumulo requires Hadoop, Zookeeper, the Accumulo master, a tablet server, etc. If
+
+you want to write a unit test that uses Accumulo, you need a lot of infrastructure
+
+in place before your test can run.</p></div>
+
+<div class="sect2">
+
+<h3 id="_mock_accumulo">5.1. Mock Accumulo</h3>
+
+<div class="paragraph"><p>Mock Accumulo supplies mock implementations for much of the client API. It presently
+
+does not enforce users, logins, permissions, etc. It does support Iterators and Combiners.
+
+Note that MockAccumulo holds all data in memory, and will not retain any data or
+
+settings between runs.</p></div>
+
+<div class="paragraph"><p>While normal interaction with the Accumulo client looks like this:</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt><span style="color: #000000">Instance</span> instance = <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">ZooKeeperInstance</span></span>(...);
+
+<span style="color: #000000">Connector</span> conn = instance.<span style="font-weight: bold"><span style="color: #000000">getConnector</span></span>(user, passwordToken);</tt></pre></div></div>
+
+<div class="paragraph"><p>To interact with the MockAccumulo, just replace the ZooKeeperInstance with MockInstance:</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt><span style="color: #000000">Instance</span> instance = <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">MockInstance</span></span>();</tt></pre></div></div>
+
+<div class="paragraph"><p>In fact, you can use the <code>--fake</code> option to the Accumulo shell and interact with
+
+MockAccumulo:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>$ ./bin/accumulo shell --fake -u root -p ''
+
+Shell - Apache Accumulo Interactive Shell
+
+-
+
+- version: 1.5
+
+- instance name: fake
+
+- instance id: mock-instance-id
+
+-
+
+- type 'help' for a list of available commands
+
+-
+
+root@fake> createtable test
+
+root@fake test> insert row1 cf cq value
+
+root@fake test> insert row2 cf cq value2
+
+root@fake test> insert row3 cf cq value3
+
+root@fake test> scan
+
+row1 cf:cq [] value
+
+row2 cf:cq [] value2
+
+row3 cf:cq [] value3
+
+root@fake test> scan -b row2 -e row2
+
+row2 cf:cq [] value2
+
+root@fake test></code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>When testing Map Reduce jobs, you can also set the Mock Accumulo on the AccumuloInputFormat
+
+and AccumuloOutputFormat classes:</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt>AccumuloInputFormat.<span style="font-weight: bold"><span style="color: #000000">setMockInstance</span></span>(job, <span style="color: #4c73a6">"mockInstance"</span>);
+
+AccumuloOutputFormat.<span style="font-weight: bold"><span style="color: #000000">setMockInstance</span></span>(job, <span style="color: #4c73a6">"mockInstance"</span>);</tt></pre></div></div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_mini_accumulo_cluster">5.2. Mini Accumulo Cluster</h3>
+
+<div class="paragraph"><p>While the Mock Accumulo provides a lightweight implementation of the client API for unit
+
+testing, it is often necessary to write more realistic end-to-end integration tests that
+
+take advantage of the entire ecosystem. The Mini Accumulo Cluster makes this possible by
+
+configuring and starting Zookeeper, initializing Accumulo, and starting the Master as well
+
+as some Tablet Servers. It runs against the local filesystem instead of having to start
+
+up HDFS.</p></div>
+
+<div class="paragraph"><p>To start it up, you will need to supply an empty directory and a root password as arguments:</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt><span style="color: #000000">File</span> tempDirectory = <span style="font-style: italic"><span style="color: #b30000">// JUnit and Guava supply mechanisms for creating temp directories</span></span>
+
+<span style="color: #000000">MiniAccumuloCluster</span> accumulo = <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">MiniAccumuloCluster</span></span>(tempDirectory, <span style="color: #4c73a6">"password"</span>);
+
+accumulo.<span style="font-weight: bold"><span style="color: #000000">start</span></span>();</tt></pre></div></div>
+
+<div class="paragraph"><p>Once we have our mini cluster running, we will want to interact with the Accumulo client API:</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt><span style="color: #000000">Instance</span> instance = <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">ZooKeeperInstance</span></span>(accumulo.<span style="font-weight: bold"><span style="color: #000000">getInstanceName</span></span>(), accumulo.<span style="font-weight: bold"><span style="color: #000000">getZooKeepers</span></span>());
+
+<span style="color: #000000">Connector</span> conn = instance.<span style="font-weight: bold"><span style="color: #000000">getConnector</span></span>(<span style="color: #4c73a6">"root"</span>, <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">PasswordToken</span></span>(<span style="color: #4c73a6">"password"</span>));</tt></pre></div></div>
+
+<div class="paragraph"><p>Upon completion of our development code, we will want to shutdown our MiniAccumuloCluster:</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt>accumulo.<span style="font-weight: bold"><span style="color: #000000">stop</span></span>()
+
+<span style="font-style: italic"><span style="color: #b30000">// delete your temporary folder</span></span></tt></pre></div></div>
+
+</div>
+
+</div>
+
+</div>
+
+<div class="sect1">
+
+<h2 id="_table_configuration">6. Table Configuration</h2>
+
+<div class="sectionbody">
+
+<div class="paragraph"><p>Accumulo tables have a few options that can be configured to alter the default
+
+behavior of Accumulo as well as improve performance based on the data stored.
+
+These include locality groups, constraints, bloom filters, iterators, and block cache.</p></div>
+
+<div class="sect2">
+
+<h3 id="_locality_groups">6.1. Locality Groups</h3>
+
+<div class="paragraph"><p>Accumulo supports storing sets of column families separately on disk to allow
+
+clients to efficiently scan over columns that are frequently used together and to avoid
+
+scanning over column families that are not requested. After a locality group is set,
+
+Scanner and BatchScanner operations will automatically take advantage of them
+
+whenever the fetchColumnFamilies() method is used.</p></div>
+
+<div class="paragraph"><p>By default, tables place all column families into the same “default” locality group.
+
+Additional locality groups can be configured anytime via the shell or
+
+programmatically as follows:</p></div>
+
+<div class="sect3">
+
+<h4 id="_managing_locality_groups_via_the_shell">6.1.1. Managing Locality Groups via the Shell</h4>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>usage: setgroups <group>=<col fam>{,<col fam>}{ <group>=<col fam>{,<col fam>}}
+
+ [-?] -t <table></code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>user@myinstance mytable> setgroups group_one=colf1,colf2 -t mytable</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>user@myinstance mytable> getgroups -t mytable</code></pre>
+
+</div></div>
+
+</div>
+
+<div class="sect3">
+
+<h4 id="_managing_locality_groups_via_the_client_api">6.1.2. Managing Locality Groups via the Client API</h4>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt><span style="color: #000000">Connector</span> conn;
+
+
+
+<span style="color: #000000">HashMap<String,Set<Text>></span> localityGroups = <span style="color: #0000b3">new</span> HashMap<String, Set<Text>>();
+
+
+
+<span style="color: #000000">HashSet<Text></span> metadataColumns = <span style="color: #0000b3">new</span> HashSet<Text>();
+
+metadataColumns.<span style="font-weight: bold"><span style="color: #000000">add</span></span>(<span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">Text</span></span>(<span style="color: #4c73a6">"domain"</span>));
+
+metadataColumns.<span style="font-weight: bold"><span style="color: #000000">add</span></span>(<span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">Text</span></span>(<span style="color: #4c73a6">"link"</span>));
+
+
+
+<span style="color: #000000">HashSet<Text></span> contentColumns = <span style="color: #0000b3">new</span> HashSet<Text>();
+
+contentColumns.<span style="font-weight: bold"><span style="color: #000000">add</span></span>(<span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">Text</span></span>(<span style="color: #4c73a6">"body"</span>));
+
+contentColumns.<span style="font-weight: bold"><span style="color: #000000">add</span></span>(<span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">Text</span></span>(<span style="color: #4c73a6">"images"</span>));
+
+
+
+localityGroups.<span style="font-weight: bold"><span style="color: #000000">put</span></span>(<span style="color: #4c73a6">"metadata"</span>, metadataColumns);
+
+localityGroups.<span style="font-weight: bold"><span style="color: #000000">put</span></span>(<span style="color: #4c73a6">"content"</span>, contentColumns);
+
+
+
+conn.<span style="font-weight: bold"><span style="color: #000000">tableOperations</span></span>().<span style="font-weight: bold"><span style="color: #000000">setLocalityGroups</span></span>(<span style="color: #4c73a6">"mytable"</span>, localityGroups);
+
+
+
+<span style="font-style: italic"><span style="color: #b30000">// existing locality groups can be obtained as follows</span></span>
+
+<span style="color: #000000">Map<String, Set<Text>></span> groups =
+
+ conn.<span style="font-weight: bold"><span style="color: #000000">tableOperations</span></span>().<span style="font-weight: bold"><span style="color: #000000">getLocalityGroups</span></span>(<span style="color: #4c73a6">"mytable"</span>);</tt></pre></div></div>
+
+<div class="paragraph"><p>The assignment of Column Families to Locality Groups can be changed at any time. The
+
+physical movement of column families into their new locality groups takes place via
+
+the periodic Major Compaction process that takes place continuously in the
+
+background. Major Compaction can also be scheduled to take place immediately
+
+through the shell:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>user@myinstance mytable> compact -t mytable</code></pre>
+
+</div></div>
+
+</div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_constraints">6.2. Constraints</h3>
+
+<div class="paragraph"><p>Accumulo supports constraints applied on mutations at insert time. This can be
+
+used to disallow certain inserts according to a user defined policy. Any mutation
+
+that fails to meet the requirements of the constraint is rejected and sent back to the
+
+client.</p></div>
+
+<div class="paragraph"><p>Constraints can be enabled by setting a table property as follows:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>user@myinstance mytable> constraint -t mytable -a com.test.ExampleConstraint com.test.AnotherConstraint
+
+user@myinstance mytable> constraint -l
+
+com.test.ExampleConstraint=1
+
+com.test.AnotherConstraint=2</code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>Currently there are no general-purpose constraints provided with the Accumulo
+
+distribution. New constraints can be created by writing a Java class that implements
+
+the org.apache.accumulo.core.constraints.Constraint interface.</p></div>
+
+<div class="paragraph"><p>To deploy a new constraint, create a jar file containing the class implementing the
+
+new constraint and place it in the lib directory of the Accumulo installation. New
+
+constraint jars can be added to Accumulo and enabled without restarting but any
+
+change to an existing constraint class requires Accumulo to be restarted.</p></div>
+
+<div class="paragraph"><p>An example of constraints can be found in
+
+<code>accumulo/docs/examples/README.constraints</code> with corresponding code under
+
+<code>accumulo/examples/simple/main/java/accumulo/examples/simple/constraints</code>.</p></div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_bloom_filters">6.3. Bloom Filters</h3>
+
+<div class="paragraph"><p>As mutations are applied to an Accumulo table, several files are created per tablet. If
+
+bloom filters are enabled, Accumulo will create and load a small data structure into
+
+memory to determine whether a file contains a given key before opening the file.
+
+This can speed up lookups considerably.</p></div>
+
+<div class="paragraph"><p>To enable bloom filters, enter the following command in the Shell:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>user@myinstance> config -t mytable -s table.bloom.enabled=true</code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>An extensive example of using Bloom Filters can be found at
+
+<code>accumulo/docs/examples/README.bloom</code>.</p></div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_iterators">6.4. Iterators</h3>
+
+<div class="paragraph"><p>Iterators provide a modular mechanism for adding functionality to be executed by
+
+TabletServers when scanning or compacting data. This allows users to efficiently
+
+summarize, filter, and aggregate data. In fact, the built-in features of cell-level
+
+security and column fetching are implemented using Iterators.
+
+Some useful Iterators are provided with Accumulo and can be found in the
+
+<strong><code>org.apache.accumulo.core.iterators.user</code></strong> package.
+
+In each case, any custom Iterators must be included in Accumulo’s classpath,
+
+typically by including a jar in <code>$ACCUMULO_HOME/lib</code> or
+
+<code>$ACCUMULO_HOME/lib/ext</code>, although the VFS classloader allows for
+
+classpath manipulation using a variety of schemes including URLs and HDFS URIs.</p></div>
+
+<div class="sect3">
+
+<h4 id="_setting_iterators_via_the_shell">6.4.1. Setting Iterators via the Shell</h4>
+
+<div class="paragraph"><p>Iterators can be configured on a table at scan, minor compaction and/or major
+
+compaction scopes. If the Iterator implements the OptionDescriber interface, the
+
+setiter command can be used which will interactively prompt the user to provide
+
+values for the given necessary options.</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>usage: setiter [-?] -ageoff | -agg | -class <name> | -regex |
+
+ -reqvis | -vers [-majc] [-minc] [-n <itername>] -p <pri>
+
+ [-scan] [-t <table>]</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>user@myinstance mytable> setiter -t mytable -scan -p 15 -n myiter -class com.company.MyIterator</code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>The config command can always be used to manually configure iterators which is useful
+
+in cases where the Iterator does not implement the OptionDescriber interface.</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>config -t mytable -s table.iterator.{scan|minc|majc}.myiter=15,com.company.MyIterator
+
+config -t mytable -s table.iteartor.{scan|minc|majc}.myiter.opt.myoptionname=myoptionvalue</code></pre>
+
+</div></div>
+
+</div>
+
+<div class="sect3">
+
+<h4 id="_setting_iterators_programmatically">6.4.2. Setting Iterators Programmatically</h4>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt>scanner.<span style="font-weight: bold"><span style="color: #000000">addIterator</span></span>(<span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">IteratorSetting</span></span>(
+
+ <span style="color: #000000">15</span>, <span style="font-style: italic"><span style="color: #b30000">// priority</span></span>
+
+ <span style="color: #4c73a6">"myiter"</span>, <span style="font-style: italic"><span style="color: #b30000">// name this iterator</span></span>
+
+ <span style="color: #4c73a6">"com.company.MyIterator"</span> <span style="font-style: italic"><span style="color: #b30000">// class name</span></span>
+
+));</tt></pre></div></div>
+
+<div class="paragraph"><p>Some iterators take additional parameters from client code, as in the following
+
+example:</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt><span style="color: #000000">IteratorSetting</span> iter = <span style="color: #0000b3">new</span> <span style="font-weight: bold"><span style="color: #000000">IteratorSetting</span></span>(...);
+
+iter.<span style="font-weight: bold"><span style="color: #000000">addOption</span></span>(<span style="color: #4c73a6">"myoptionname"</span>, <span style="color: #4c73a6">"myoptionvalue"</span>);
+
+scanner.<span style="font-weight: bold"><span style="color: #000000">addIterator</span></span>(iter)</tt></pre></div></div>
+
+<div class="paragraph"><p>Tables support separate Iterator settings to be applied at scan time, upon minor
+
+compaction and upon major compaction. For most uses, tables will have identical
+
+iterator settings for all three to avoid inconsistent results.</p></div>
+
+</div>
+
+<div class="sect3">
+
+<h4 id="_versioning_iterators_and_timestamps">6.4.3. Versioning Iterators and Timestamps</h4>
+
+<div class="paragraph"><p>Accumulo provides the capability to manage versioned data through the use of
+
+timestamps within the Key. If a timestamp is not specified in the key created by the
+
+client then the system will set the timestamp to the current time. Two keys with
+
+identical rowIDs and columns but different timestamps are considered two versions
+
+of the same key. If two inserts are made into accumulo with the same rowID,
+
+column, and timestamp, then the behavior is non-deterministic.</p></div>
+
+<div class="paragraph"><p>Timestamps are sorted in descending order, so the most recent data comes first.
+
+Accumulo can be configured to return the top k versions, or versions later than a
+
+given date. The default is to return the one most recent version.</p></div>
+
+<div class="paragraph"><p>The version policy can be changed by changing the VersioningIterator options for a
+
+table as follows:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>user@myinstance mytable> config -t mytable -s table.iterator.scan.vers.opt.maxVersions=3
+
+user@myinstance mytable> config -t mytable -s table.iterator.minc.vers.opt.maxVersions=3
+
+user@myinstance mytable> config -t mytable -s table.iterator.majc.vers.opt.maxVersions=3</code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>When a table is created, by default its configured to use the
+
+VersioningIterator and keep one version. A table can be created without the
+
+VersioningIterator with the -ndi option in the shell. Also the Java API
+
+has the following method</p></div>
+
+<div class="listingblock">
+
+<div class="content"><!-- Generator: GNU source-highlight 3.1.4
+
+by Lorenzo Bettini
+
+http://www.lorenzobettini.it
+
+http://www.gnu.org/software/src-highlite -->
+
+<pre><tt>connector.tableOperations.<span style="font-weight: bold"><span style="color: #000000">create</span></span>(<span style="color: #000000">String</span> tableName, <span style="color: #000000">boolean</span> limitVersion)</tt></pre></div></div>
+
+<div class="sect4">
+
+<h5 id="_logical_time">Logical Time</h5>
+
+<div class="paragraph"><p>Accumulo 1.2 introduces the concept of logical time. This ensures that timestamps
+
+set by accumulo always move forward. This helps avoid problems caused by
+
+TabletServers that have different time settings. The per tablet counter gives unique
+
+one up time stamps on a per mutation basis. When using time in milliseconds, if
+
+two things arrive within the same millisecond then both receive the same
+
+timestamp. When using time in milliseconds, accumulo set times will still
+
+always move forward and never backwards.</p></div>
+
+<div class="paragraph"><p>A table can be configured to use logical timestamps at creation time as follows:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>user@myinstance> createtable -tl logical</code></pre>
+
+</div></div>
+
+</div>
+
+<div class="sect4">
+
+<h5 id="_deletes">Deletes</h5>
+
+<div class="paragraph"><p>Deletes are special keys in accumulo that get sorted along will all the other data.
+
+When a delete key is inserted, accumulo will not show anything that has a
+
+timestamp less than or equal to the delete key. During major compaction, any keys
+
+older than a delete key are omitted from the new file created, and the omitted keys
+
+are removed from disk as part of the regular garbage collection process.</p></div>
+
+</div>
+
+</div>
+
+<div class="sect3">
+
+<h4 id="_filters">6.4.4. Filters</h4>
+
+<div class="paragraph"><p>When scanning over a set of key-value pairs it is possible to apply an arbitrary
+
+filtering policy through the use of a Filter. Filters are types of iterators that return
+
+only key-value pairs that satisfy the filter logic. Accumulo has a few built-in filters
+
+that can be configured on any table: AgeOff, ColumnAgeOff, Timestamp, NoVis, and RegEx. More can be added
+
+by writing a Java class that extends the
+
+<code>org.apache.accumulo.core.iterators.Filter</code> class.</p></div>
+
+<div class="paragraph"><p>The AgeOff filter can be configured to remove data older than a certain date or a fixed
+
+amount of time from the present. The following example sets a table to delete
+
+everything inserted over 30 seconds ago:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>user@myinstance> createtable filtertest
+
+user@myinstance filtertest> setiter -t filtertest -scan -minc -majc -p 10 -n myfilter -ageoff
+
+AgeOffFilter removes entries with timestamps more than <ttl> milliseconds old
+
+----------> set org.apache.accumulo.core.iterators.user.AgeOffFilter parameter
+
+ negate, default false keeps k/v that pass accept method, true rejects k/v
+
+ that pass accept method:
+
+----------> set org.apache.accumulo.core.iterators.user.AgeOffFilter parameter
+
+ ttl, time to live (milliseconds): 3000
+
+----------> set org.apache.accumulo.core.iterators.user.AgeOffFilter parameter
+
+ currentTime, if set, use the given value as the absolute time in milliseconds
+
+ as the current time of day:
+
+user@myinstance filtertest>
+
+user@myinstance filtertest> scan
+
+user@myinstance filtertest> insert foo a b c
+
+user@myinstance filtertest> scan
+
+foo a:b [] c
+
+user@myinstance filtertest> sleep 4
+
+user@myinstance filtertest> scan
+
+user@myinstance filtertest></code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>To see the iterator settings for a table, use:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>user@example filtertest> config -t filtertest -f iterator
+
+---------+---------------------------------------------+------------------
+
+SCOPE | NAME | VALUE
+
+---------+---------------------------------------------+------------------
+
+table | table.iterator.majc.myfilter .............. | 10,org.apache.accumulo.core.iterators.user.AgeOffFilter
+
+table | table.iterator.majc.myfilter.opt.ttl ...... | 3000
+
+table | table.iterator.majc.vers .................. | 20,org.apache.accumulo.core.iterators.VersioningIterator
+
+table | table.iterator.majc.vers.opt.maxVersions .. | 1
+
+table | table.iterator.minc.myfilter .............. | 10,org.apache.accumulo.core.iterators.user.AgeOffFilter
+
+table | table.iterator.minc.myfilter.opt.ttl ...... | 3000
+
+table | table.iterator.minc.vers .................. | 20,org.apache.accumulo.core.iterators.VersioningIterator
+
+table | table.iterator.minc.vers.opt.maxVersions .. | 1
+
+table | table.iterator.scan.myfilter .............. | 10,org.apache.accumulo.core.iterators.user.AgeOffFilter
+
+table | table.iterator.scan.myfilter.opt.ttl ...... | 3000
+
+table | table.iterator.scan.vers .................. | 20,org.apache.accumulo.core.iterators.VersioningIterator
+
+table | table.iterator.scan.vers.opt.maxVersions .. | 1
+
+---------+---------------------------------------------+------------------</code></pre>
+
+</div></div>
+
+</div>
+
+<div class="sect3">
+
+<h4 id="_combiners">6.4.5. Combiners</h4>
+
+<div class="paragraph"><p>Accumulo allows Combiners to be configured on tables and column
+
+families. When a Combiner is set it is applied across the values
+
+associated with any keys that share rowID, column family, and column qualifier.
+
+This is similar to the reduce step in MapReduce, which applied some function to all
+
+the values associated with a particular key.</p></div>
+
+<div class="paragraph"><p>For example, if a summing combiner were configured on a table and the following
+
+mutations were inserted:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>Row Family Qualifier Timestamp Value
+
+rowID1 colfA colqA 20100101 1
+
+rowID1 colfA colqA 20100102 1</code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>The table would reflect only one aggregate value:</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>rowID1 colfA colqA - 2</code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>Combiners can be enabled for a table using the setiter command in the shell. Below is an example.</p></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@a14 perDayCounts> setiter -t perDayCounts -p 10 -scan -minc -majc -n daycount -class org.apache.accumulo.core.iterators.user.SummingCombiner
+
+TypedValueCombiner can interpret Values as a variety of number encodings
+
+ (VLong, Long, or String) before combining
+
+----------> set SummingCombiner parameter columns,
+
+ <col fam>[:<col qual>]{,<col fam>[:<col qual>]} : day
+
+----------> set SummingCombiner parameter type, <VARNUM|LONG|STRING>: STRING</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@a14 perDayCounts> insert foo day 20080101 1
+
+root@a14 perDayCounts> insert foo day 20080101 1
+
+root@a14 perDayCounts> insert foo day 20080103 1
+
+root@a14 perDayCounts> insert bar day 20080101 1
+
+root@a14 perDayCounts> insert bar day 20080101 1</code></pre>
+
+</div></div>
+
+<div class="literalblock">
+
+<div class="content">
+
+<pre><code>root@a14 perDayCounts> scan
+
+bar day:20080101 [] 2
+
+foo day:20080101 [] 2
+
+foo day:20080103 [] 1</code></pre>
+
+</div></div>
+
+<div class="paragraph"><p>Accumulo includes some useful Combiners out of the box. To find these look in
+
+the <strong><code>org.apache.accumulo.core.iterators.user</code></strong> package.</p></div>
+
+<div class="paragraph"><p>Additional Combiners can be added by creating a Java class that extends
+
+<code>org.apache.accumulo.core.iterators.Combiner</code> and adding a jar containing that
+
+class to Accumulo’s lib/ext directory.</p></div>
+
+<div class="paragraph"><p>An example of a Combiner can be found under
+
+<code>accumulo/examples/simple/main/java/org/apache/accumulo/examples/simple/combiner/StatsCombiner.java</code></p></div>
+
+</div>
+
+</div>
+
+<div class="sect2">
+
+<h3 id="_block_cache">6.5. Block Cache</h3>
+
+<div class="paragraph"><p>In order to increase throughput of commonly accessed entries, Accumulo employs a block cache.
+
+This block cache buffers data in memory so that it doesn’t have to be read off of disk.
+
+The RFile format that Accumulo prefers is a mix of index blocks and data blocks, where the index blocks are used to find the appropriate data blocks.
+
+Typical queries to Accumulo result in a binary search over several index blocks followed by a linear scan of one or more data blocks.</p></div>
+
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