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Posted to commits@accumulo.apache.org by bu...@apache.org on 2011/11/01 18:08:19 UTC
svn commit: r797867 [11/12] - in /websites/staging/accumulo/trunk/content:
./ accumulo/ accumulo/css/ accumulo/governance/ accumulo/images/
accumulo/user_manual_1.3-incubating/
accumulo/user_manual_1.3-incubating/examples/
accumulo/user_manual_1.4-incu...
Added: websites/staging/accumulo/trunk/content/accumulo/user_manual_1.4-incubating/Table_Configuration.html
==============================================================================
--- websites/staging/accumulo/trunk/content/accumulo/user_manual_1.4-incubating/Table_Configuration.html (added)
+++ websites/staging/accumulo/trunk/content/accumulo/user_manual_1.4-incubating/Table_Configuration.html Tue Nov 1 17:08:17 2011
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+ <h1 class="title">Accumulo User Manual: Table Configuration</h1>
+ <p><strong> Next:</strong> <a href="Table_Design.html">Table Design</a> <strong> Up:</strong> <a href="accumulo_user_manual.html">Accumulo User Manual Version 1.4</a> <strong> Previous:</strong> <a href="Writing_Accumulo_Clients.html">Writing Accumulo Clients</a> <strong> <a href="Contents.html">Contents</a></strong> <br />
+</p>
+<p><a id=CHILD_LINKS></a><strong>Subsections</strong></p>
+<ul>
+<li><a href="Table_Configuration.html#Locality_Groups">Locality Groups</a></li>
+<li><a href="Table_Configuration.html#Constraints">Constraints</a></li>
+<li><a href="Table_Configuration.html#Bloom_Filters">Bloom Filters</a></li>
+<li><a href="Table_Configuration.html#Iterators">Iterators</a></li>
+<li><a href="Table_Configuration.html#Versioning_Iterators_and_Timestamps">Versioning Iterators and Timestamps</a></li>
+<li><a href="Table_Configuration.html#Filters">Filters</a></li>
+<li><a href="Table_Configuration.html#Aggregating_Iterators">Aggregating Iterators</a></li>
+<li><a href="Table_Configuration.html#Pre-splitting_tables">Pre-splitting tables</a></li>
+<li><a href="Table_Configuration.html#Merging_tablets">Merging tablets</a></li>
+<li><a href="Table_Configuration.html#Delete_Range">Delete Range</a></li>
+<li><a href="Table_Configuration.html#Cloning_Tables">Cloning Tables</a></li>
+</ul>
+<hr />
+<h2 id="a_idtable_configurationa_table_configuration"><a id=Table_Configuration></a> Table Configuration</h2>
+<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, and iterators. </p>
+<h2 id="a_idlocality_groupsa_locality_groups"><a id=Locality_Groups></a> Locality Groups</h2>
+<p>Accumulo supports storing of sets of column families separately on disk to allow clients to scan over columns that are frequently used together efficient 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>
+<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>
+<h3 id="a_idmanaging_locality_groups_via_the_shella_managing_locality_groups_via_the_shell"><a id=Managing_Locality_Groups_via_the_Shell></a> Managing Locality Groups via the Shell</h3>
+<div class="codehilite"><pre><span class="err">usage:</span> <span class="err">setgroups</span> <span class="err"><group>=<col</span> <span class="err">fam>{,<col</span> <span class="err">fam>}{</span> <span class="err"><group>=<col</span> <span class="err">fam>{,<col</span>
+<span class="err">fam>}}</span> <span class="err">[-?]</span> <span class="err">-t</span> <span class="err"><table></span>
+
+<span class="err">user@myinstance</span> <span class="err">mytable></span> <span class="err">setgroups</span> <span class="err">-t</span> <span class="err">mytable</span> <span class="err">group_one=colf1,colf2</span>
+
+<span class="err">user@myinstance</span> <span class="err">mytable></span> <span class="err">getgroups</span> <span class="err">-t</span> <span class="err">mytable</span>
+<span class="err">group_one=colf1,colf2</span>
+</pre></div>
+
+
+<h3 id="a_idmanaging_locality_groups_via_the_client_apia_managing_locality_groups_via_the_client_api"><a id=Managing_Locality_Groups_via_the_Client_API></a> Managing Locality Groups via the Client API</h3>
+<div class="codehilite"><pre><span class="n">Connector</span> <span class="n">conn</span><span class="p">;</span>
+
+<span class="n">HashMap</span><span class="sr"><String,Set<Text></span><span class="o">></span> <span class="n">localityGroups</span> <span class="o">=</span>
+ <span class="k">new</span> <span class="n">HashMap</span><span class="o"><</span><span class="n">String</span><span class="p">,</span> <span class="n">Set</span><span class="sr"><Text></span><span class="o">></span><span class="p">();</span>
+
+<span class="n">HashSet</span><span class="sr"><Text></span> <span class="n">metadataColumns</span> <span class="o">=</span> <span class="k">new</span> <span class="n">HashSet</span><span class="sr"><Text></span><span class="p">();</span>
+<span class="n">metadataColumns</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="k">new</span> <span class="n">Text</span><span class="p">(</span><span class="s">"domain"</span><span class="p">));</span>
+<span class="n">metadataColumns</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="k">new</span> <span class="n">Text</span><span class="p">(</span><span class="s">"link"</span><span class="p">));</span>
+
+<span class="n">HashSet</span><span class="sr"><Text></span> <span class="n">contentColumns</span> <span class="o">=</span> <span class="k">new</span> <span class="n">HashSet</span><span class="sr"><Text></span><span class="p">();</span>
+<span class="n">contentColumns</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="k">new</span> <span class="n">Text</span><span class="p">(</span><span class="s">"body"</span><span class="p">));</span>
+<span class="n">contentColumns</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="k">new</span> <span class="n">Text</span><span class="p">(</span><span class="s">"images"</span><span class="p">));</span>
+
+<span class="n">localityGroups</span><span class="o">.</span><span class="n">put</span><span class="p">(</span><span class="s">"metadata"</span><span class="p">,</span> <span class="n">metadataColumns</span><span class="p">);</span>
+<span class="n">localityGroups</span><span class="o">.</span><span class="n">put</span><span class="p">(</span><span class="s">"content"</span><span class="p">,</span> <span class="n">contentColumns</span><span class="p">);</span>
+
+<span class="n">conn</span><span class="o">.</span><span class="n">tableOperations</span><span class="p">()</span><span class="o">.</span><span class="n">setLocalityGroups</span><span class="p">(</span><span class="s">"mytable"</span><span class="p">,</span> <span class="n">localityGroups</span><span class="p">);</span>
+
+<span class="sr">//</span> <span class="n">existing</span> <span class="n">locality</span> <span class="n">groups</span> <span class="n">can</span> <span class="n">be</span> <span class="n">obtained</span> <span class="n">as</span> <span class="n">follows</span>
+<span class="n">Map</span><span class="o"><</span><span class="n">String</span><span class="p">,</span> <span class="n">Set</span><span class="sr"><Text></span><span class="o">></span> <span class="n">groups</span> <span class="o">=</span>
+ <span class="n">conn</span><span class="o">.</span><span class="n">tableOperations</span><span class="p">()</span><span class="o">.</span><span class="n">getLocalityGroups</span><span class="p">(</span><span class="s">"mytable"</span><span class="p">);</span>
+</pre></div>
+
+
+<p>The assignment of Column Families to Locality Groups can be changed anytime. 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 class="codehilite"><pre><span class="n">user</span><span class="nv">@myinstance</span> <span class="n">mytable</span><span class="o">></span> <span class="n">compact</span> <span class="o">-</span><span class="n">t</span> <span class="n">mytable</span>
+</pre></div>
+
+
+<h2 id="a_idconstraintsa_constraints"><a id=Constraints></a> Constraints</h2>
+<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>
+<p>Constraints can be enabled by setting a table property as follows: </p>
+<div class="codehilite"><pre><span class="n">user</span><span class="nv">@myinstance</span> <span class="n">mytable</span><span class="o">></span> <span class="n">config</span> <span class="o">-</span><span class="n">t</span> <span class="n">mytable</span> <span class="o">-</span><span class="n">s</span> <span class="n">table</span><span class="o">.</span><span class="n">constraint</span><span class="mf">.1</span><span class="o">=</span><span class="n">com</span><span class="o">.</span><span class="n">test</span><span class="o">.</span><span class="n">ExampleConstraint</span>
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">mytable</span><span class="o">></span> <span class="n">config</span> <span class="o">-</span><span class="n">t</span> <span class="n">mytable</span> <span class="o">-</span><span class="n">s</span> <span class="n">table</span><span class="o">.</span><span class="n">constraint</span><span class="mf">.2</span><span class="o">=</span><span class="n">com</span><span class="o">.</span><span class="n">test</span><span class="o">.</span><span class="n">AnotherConstraint</span>
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">mytable</span><span class="o">></span> <span class="n">config</span> <span class="o">-</span><span class="n">t</span> <span class="n">mytable</span> <span class="o">-</span><span class="n">f</span> <span class="n">constraint</span>
+<span class="o">---------+--------------------------------+----------------------------</span>
+<span class="n">SCOPE</span> <span class="o">|</span> <span class="n">NAME</span> <span class="o">|</span> <span class="n">VALUE</span>
+<span class="o">---------+--------------------------------+----------------------------</span>
+<span class="n">table</span> <span class="o">|</span> <span class="n">table</span><span class="o">.</span><span class="n">constraint</span><span class="mf">.1</span><span class="o">............</span> <span class="o">|</span> <span class="n">com</span><span class="o">.</span><span class="n">test</span><span class="o">.</span><span class="n">ExampleConstraint</span>
+<span class="n">table</span> <span class="o">|</span> <span class="n">table</span><span class="o">.</span><span class="n">constraint</span><span class="mf">.2</span><span class="o">............</span> <span class="o">|</span> <span class="n">com</span><span class="o">.</span><span class="n">test</span><span class="o">.</span><span class="n">AnotherConstraint</span>
+<span class="o">---------+--------------------------------+----------------------------</span>
+</pre></div>
+
+
+<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>
+<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>
+<p>An example of constraints can be found in <br />
+accumulo/docs/examples/README.constraints with corresponding code under <br />
+accumulo/src/examples/main/java/accumulo/examples/constraints . </p>
+<h2 id="a_idbloom_filtersa_bloom_filters"><a id=Bloom_Filters></a> Bloom Filters</h2>
+<p>As mutations are applied to a 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>
+<p>To enable bloom filters, enter the following command in the Shell: </p>
+<div class="codehilite"><pre><span class="n">user</span><span class="nv">@myinstance</span><span class="o">></span> <span class="n">config</span> <span class="o">-</span><span class="n">t</span> <span class="n">mytable</span> <span class="o">-</span><span class="n">s</span> <span class="n">table</span><span class="o">.</span><span class="n">bloom</span><span class="o">.</span><span class="n">enabled</span><span class="o">=</span><span class="n">true</span>
+</pre></div>
+
+
+<p>An extensive example of using Bloom Filters can be found at <br />
+accumulo/docs/examples/README.bloom . </p>
+<h2 id="a_iditeratorsa_iterators"><a id=Iterators></a> Iterators</h2>
+<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 org.apache.accumulo.core.iterators.user package. </p>
+<h3 id="a_idsetting_iterators_via_the_shella_setting_iterators_via_the_shell"><a id=Setting_Iterators_via_the_Shell></a> Setting Iterators via the Shell</h3>
+<div class="codehilite"><pre><span class="err">usage:</span> <span class="err">setiter</span> <span class="err">[-?]</span> <span class="err">-agg</span> <span class="err">|</span> <span class="err">-</span><span class="kd">class</span> <span class="p"><</span><span class="err">name</span><span class="p">></span> <span class="err">|</span> <span class="err">-filter</span> <span class="err">|</span> <span class="err">-nolabel</span> <span class="err">|</span>
+<span class="err">-regex</span> <span class="err">|</span> <span class="err">-vers</span> <span class="err">[-majc]</span> <span class="err">[-minc]</span> <span class="err">[-n</span> <span class="err"><itername>]</span> <span class="err">-p</span> <span class="err"><pri></span> <span class="err">[-scan]</span>
+<span class="err">[-t</span> <span class="err"><table>]</span>
+
+<span class="err">user@myinstance</span> <span class="err">mytable></span> <span class="err">setiter</span> <span class="err">-t</span> <span class="err">mytable</span> <span class="err">-scan</span> <span class="err">-p</span> <span class="err">10</span> <span class="err">-n</span> <span class="err">myiter</span>
+</pre></div>
+
+
+<h3 id="a_idsetting_iterators_programmaticallya_setting_iterators_programmatically"><a id=Setting_Iterators_Programmatically></a> Setting Iterators Programmatically</h3>
+<div class="codehilite"><pre><span class="n">scanner</span><span class="o">.</span><span class="n">addIterator</span><span class="p">(</span><span class="k">new</span> <span class="n">IteratorSetting</span><span class="p">(</span>
+ <span class="mi">15</span><span class="p">,</span> <span class="sr">//</span> <span class="n">priority</span>
+ <span class="s">"com.company.MyIterator"</span><span class="p">,</span> <span class="sr">//</span> <span class="n">class</span> <span class="n">name</span>
+ <span class="s">"myiter"</span> <span class="sr">//</span> <span class="n">name</span> <span class="n">this</span> <span class="n">iterator</span>
+<span class="p">));</span>
+</pre></div>
+
+
+<p>Some iterators take additional parameters from client code, as in the following example: </p>
+<div class="codehilite"><pre><span class="n">IteratorSetting</span> <span class="n">iter</span> <span class="o">=</span> <span class="k">new</span> <span class="n">IteratorSetting</span><span class="p">(</span><span class="o">...</span><span class="p">);</span>
+<span class="n">iter</span><span class="o">.</span><span class="n">addOption</span><span class="p">(</span><span class="s">"myoptionname"</span><span class="p">,</span> <span class="s">"myoptionvalue"</span><span class="p">);</span>
+<span class="n">scanner</span><span class="o">.</span><span class="n">addIterator</span><span class="p">(</span><span class="n">iter</span><span class="p">)</span>
+</pre></div>
+
+
+<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>
+<h2 id="a_idversioning_iterators_and_timestampsa_versioning_iterators_and_timestamps"><a id=Versioning_Iterators_and_Timestamps></a> Versioning Iterators and Timestamps</h2>
+<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>
+<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>
+<p>The version policy can be changed by changing the VersioningIterator options for a table as follows: </p>
+<div class="codehilite"><pre><span class="n">user</span><span class="nv">@myinstance</span> <span class="n">mytable</span><span class="o">></span> <span class="n">config</span> <span class="o">-</span><span class="n">t</span> <span class="n">mytable</span> <span class="o">-</span><span class="n">s</span>
+<span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">scan</span><span class="o">.</span><span class="n">vers</span><span class="o">.</span><span class="n">opt</span><span class="o">.</span><span class="n">maxVersions</span><span class="o">=</span><span class="mi">3</span>
+
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">mytable</span><span class="o">></span> <span class="n">config</span> <span class="o">-</span><span class="n">t</span> <span class="n">mytable</span> <span class="o">-</span><span class="n">s</span>
+<span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">minc</span><span class="o">.</span><span class="n">vers</span><span class="o">.</span><span class="n">opt</span><span class="o">.</span><span class="n">maxVersions</span><span class="o">=</span><span class="mi">3</span>
+
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">mytable</span><span class="o">></span> <span class="n">config</span> <span class="o">-</span><span class="n">t</span> <span class="n">mytable</span> <span class="o">-</span><span class="n">s</span>
+<span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">majc</span><span class="o">.</span><span class="n">vers</span><span class="o">.</span><span class="n">opt</span><span class="o">.</span><span class="n">maxVersions</span><span class="o">=</span><span class="mi">3</span>
+</pre></div>
+
+
+<h3 id="a_idlogical_timea_logical_time"><a id=Logical_Time></a> Logical Time</h3>
+<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>
+<p>A table can be configured to use logical timestamps at creation time as follows: </p>
+<div class="codehilite"><pre><span class="n">user</span><span class="nv">@myinstance</span><span class="o">></span> <span class="n">createtable</span> <span class="o">-</span><span class="n">tl</span> <span class="n">logical</span>
+</pre></div>
+
+
+<h3 id="a_iddeletesa_deletes"><a id=Deletes></a> Deletes</h3>
+<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>
+<h2 id="a_idfiltersa_filters"><a id=Filters></a> Filters</h2>
+<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 <br />
+org.apache.accumulo.core.iterators.Filter class. </p>
+<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 class="codehilite"><pre><span class="n">user</span><span class="nv">@myinstance</span><span class="o">></span> <span class="n">createtable</span> <span class="n">filtertest</span>
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">filtertest</span><span class="o">></span> <span class="n">setiter</span> <span class="o">-</span><span class="n">t</span> <span class="n">filtertest</span> <span class="o">-</span><span class="n">scan</span> <span class="o">-</span><span class="n">minc</span> <span class="o">-</span><span class="n">majc</span> <span class="o">-</span><span class="n">p</span> <span class="mi">10</span> <span class="o">-</span><span class="n">n</span> <span class="n">myfilter</span> <span class="o">-</span><span class="n">ageoff</span>
+<span class="n">AgeOffFilter</span> <span class="n">removes</span> <span class="n">entries</span> <span class="n">with</span> <span class="n">timestamps</span> <span class="n">more</span> <span class="n">than</span> <span class="sr"><ttl></span> <span class="n">milliseconds</span> <span class="n">old</span>
+<span class="o">----------></span> <span class="n">set</span> <span class="n">org</span><span class="o">.</span><span class="n">apache</span><span class="o">.</span><span class="n">accumulo</span><span class="o">.</span><span class="n">core</span><span class="o">.</span><span class="n">iterators</span><span class="o">.</span><span class="n">user</span><span class="o">.</span><span class="n">AgeOffFilter</span> <span class="n">parameter</span> <span class="n">negate</span><span class="p">,</span> <span class="n">default</span> <span class="n">false</span> <span class="n">keeps</span> <span class="n">k</span><span class="sr">/v that pass accept method, true rejects k/</span><span class="n">v</span> <span class="n">that</span> <span class="n">pass</span> <span class="nb">accept</span> <span class="n">method:</span>
+<span class="o">----------></span> <span class="n">set</span> <span class="n">org</span><span class="o">.</span><span class="n">apache</span><span class="o">.</span><span class="n">accumulo</span><span class="o">.</span><span class="n">core</span><span class="o">.</span><span class="n">iterators</span><span class="o">.</span><span class="n">user</span><span class="o">.</span><span class="n">AgeOffFilter</span> <span class="n">parameter</span> <span class="n">ttl</span><span class="p">,</span> <span class="nb">time</span> <span class="n">to</span> <span class="n">live</span> <span class="p">(</span><span class="n">milliseconds</span><span class="p">):</span> <span class="mi">3000</span>
+<span class="o">----------></span> <span class="n">set</span> <span class="n">org</span><span class="o">.</span><span class="n">apache</span><span class="o">.</span><span class="n">accumulo</span><span class="o">.</span><span class="n">core</span><span class="o">.</span><span class="n">iterators</span><span class="o">.</span><span class="n">user</span><span class="o">.</span><span class="n">AgeOffFilter</span> <span class="n">parameter</span> <span class="n">currentTime</span><span class="p">,</span> <span class="k">if</span> <span class="n">set</span><span class="p">,</span> <span class="k">use</span> <span class="n">the</span> <span class="n">given</span> <span class="n">value</span> <span class="n">as</span> <span class="n">the</span> <span class="n">absolute</span> <span class="nb">time</span> <span class="n">in</span> <span class="n">milliseconds</span> <span class="n">as</span> <span class="n">the</span> <span class="n">current</span> <span class="nb">time</span> <s
pan class="n">of</span> <span class="n">day:</span>
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">filtertest</span><span class="o">></span>
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">filtertest</span><span class="o">></span> <span class="n">scan</span>
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">filtertest</span><span class="o">></span> <span class="n">insert</span> <span class="n">foo</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span>
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">filtertest</span><span class="o">></span> <span class="n">scan</span>
+<span class="n">foo</span> <span class="n">a:b</span> <span class="o">[]</span> <span class="n">c</span>
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">filtertest</span><span class="o">></span> <span class="nb">sleep</span> <span class="mi">4</span>
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">filtertest</span><span class="o">></span> <span class="n">scan</span>
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">filtertest</span><span class="o">></span>
+</pre></div>
+
+
+<p>To see the iterator settings for a table, use: </p>
+<div class="codehilite"><pre><span class="n">user</span><span class="nv">@example</span> <span class="n">filtertest</span><span class="o">></span> <span class="n">config</span> <span class="o">-</span><span class="n">t</span> <span class="n">filtertest</span> <span class="o">-</span><span class="n">f</span> <span class="n">iterator</span>
+<span class="o">---------+---------------------------------------------+------------------</span>
+<span class="n">SCOPE</span> <span class="o">|</span> <span class="n">NAME</span> <span class="o">|</span> <span class="n">VALUE</span>
+<span class="o">---------+---------------------------------------------+------------------</span>
+<span class="n">table</span> <span class="o">|</span> <span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">majc</span><span class="o">.</span><span class="n">myfilter</span> <span class="o">..............</span> <span class="o">|</span> <span class="mi">10</span><span class="p">,</span><span class="n">org</span><span class="o">.</span><span class="n">apache</span><span class="o">.</span><span class="n">accumulo</span><span class="o">.</span><span class="n">core</span><span class="o">.</span><span class="n">iterators</span><span class="o">.</span><span class="n">user</span><span class="o">.</span><span class="n">AgeOffFilter</span>
+<span class="n">table</span> <span class="o">|</span> <span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">majc</span><span class="o">.</span><span class="n">myfilter</span><span class="o">.</span><span class="n">opt</span><span class="o">.</span><span class="n">ttl</span> <span class="o">......</span> <span class="o">|</span> <span class="mi">3000</span>
+<span class="n">table</span> <span class="o">|</span> <span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">majc</span><span class="o">.</span><span class="n">vers</span> <span class="o">..................</span> <span class="o">|</span> <span class="mi">20</span><span class="p">,</span><span class="n">org</span><span class="o">.</span><span class="n">apache</span><span class="o">.</span><span class="n">accumulo</span><span class="o">.</span><span class="n">core</span><span class="o">.</span><span class="n">iterators</span><span class="o">.</span><span class="n">VersioningIterator</span>
+<span class="n">table</span> <span class="o">|</span> <span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">majc</span><span class="o">.</span><span class="n">vers</span><span class="o">.</span><span class="n">opt</span><span class="o">.</span><span class="n">maxVersions</span> <span class="o">..</span> <span class="o">|</span> <span class="mi">1</span>
+<span class="n">table</span> <span class="o">|</span> <span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">minc</span><span class="o">.</span><span class="n">myfilter</span> <span class="o">..............</span> <span class="o">|</span> <span class="mi">10</span><span class="p">,</span><span class="n">org</span><span class="o">.</span><span class="n">apache</span><span class="o">.</span><span class="n">accumulo</span><span class="o">.</span><span class="n">core</span><span class="o">.</span><span class="n">iterators</span><span class="o">.</span><span class="n">user</span><span class="o">.</span><span class="n">AgeOffFilter</span>
+<span class="n">table</span> <span class="o">|</span> <span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">minc</span><span class="o">.</span><span class="n">myfilter</span><span class="o">.</span><span class="n">opt</span><span class="o">.</span><span class="n">ttl</span> <span class="o">......</span> <span class="o">|</span> <span class="mi">3000</span>
+<span class="n">table</span> <span class="o">|</span> <span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">minc</span><span class="o">.</span><span class="n">vers</span> <span class="o">..................</span> <span class="o">|</span> <span class="mi">20</span><span class="p">,</span><span class="n">org</span><span class="o">.</span><span class="n">apache</span><span class="o">.</span><span class="n">accumulo</span><span class="o">.</span><span class="n">core</span><span class="o">.</span><span class="n">iterators</span><span class="o">.</span><span class="n">VersioningIterator</span>
+<span class="n">table</span> <span class="o">|</span> <span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">minc</span><span class="o">.</span><span class="n">vers</span><span class="o">.</span><span class="n">opt</span><span class="o">.</span><span class="n">maxVersions</span> <span class="o">..</span> <span class="o">|</span> <span class="mi">1</span>
+<span class="n">table</span> <span class="o">|</span> <span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">scan</span><span class="o">.</span><span class="n">myfilter</span> <span class="o">..............</span> <span class="o">|</span> <span class="mi">10</span><span class="p">,</span><span class="n">org</span><span class="o">.</span><span class="n">apache</span><span class="o">.</span><span class="n">accumulo</span><span class="o">.</span><span class="n">core</span><span class="o">.</span><span class="n">iterators</span><span class="o">.</span><span class="n">user</span><span class="o">.</span><span class="n">AgeOffFilter</span>
+<span class="n">table</span> <span class="o">|</span> <span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">scan</span><span class="o">.</span><span class="n">myfilter</span><span class="o">.</span><span class="n">opt</span><span class="o">.</span><span class="n">ttl</span> <span class="o">......</span> <span class="o">|</span> <span class="mi">3000</span>
+<span class="n">table</span> <span class="o">|</span> <span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">scan</span><span class="o">.</span><span class="n">vers</span> <span class="o">..................</span> <span class="o">|</span> <span class="mi">20</span><span class="p">,</span><span class="n">org</span><span class="o">.</span><span class="n">apache</span><span class="o">.</span><span class="n">accumulo</span><span class="o">.</span><span class="n">core</span><span class="o">.</span><span class="n">iterators</span><span class="o">.</span><span class="n">VersioningIterator</span>
+<span class="n">table</span> <span class="o">|</span> <span class="n">table</span><span class="o">.</span><span class="n">iterator</span><span class="o">.</span><span class="n">scan</span><span class="o">.</span><span class="n">vers</span><span class="o">.</span><span class="n">opt</span><span class="o">.</span><span class="n">maxVersions</span> <span class="o">..</span> <span class="o">|</span> <span class="mi">1</span>
+<span class="o">---------+------------------------------------------+------------------</span>
+</pre></div>
+
+
+<h2 id="a_idaggregating_iteratorsa_aggregating_iterators"><a id=Aggregating_Iterators></a> Aggregating Iterators</h2>
+<p>Accumulo allows aggregating iterators to be configured on tables and column families. When an aggregating iterator is set, the iterator 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>
+<p>For example, if an aggregating iterator were configured on a table and the following mutations were inserted: </p>
+<div class="codehilite"><pre><span class="n">Row</span> <span class="n">Family</span> <span class="n">Qualifier</span> <span class="n">Timestamp</span> <span class="n">Value</span>
+<span class="n">rowID1</span> <span class="n">colfA</span> <span class="n">colqA</span> <span class="mi">20100101</span> <span class="mi">1</span>
+<span class="n">rowID1</span> <span class="n">colfA</span> <span class="n">colqA</span> <span class="mi">20100102</span> <span class="mi">1</span>
+</pre></div>
+
+
+<p>The table would reflect only one aggregate value: </p>
+<div class="codehilite"><pre><span class="n">rowID1</span> <span class="n">colfA</span> <span class="n">colqA</span> <span class="o">-</span> <span class="mi">2</span>
+</pre></div>
+
+
+<p>Aggregating iterators can be enabled for a table as follows: </p>
+<div class="codehilite"><pre><span class="n">user</span><span class="nv">@myinstance</span><span class="o">></span> <span class="n">createtable</span> <span class="n">perDayCounts</span> <span class="o">-</span><span class="n">a</span>
+<span class="n">day</span><span class="o">=</span><span class="n">org</span><span class="o">.</span><span class="n">apache</span><span class="o">.</span><span class="n">accumulo</span><span class="o">.</span><span class="n">core</span><span class="o">.</span><span class="n">iterators</span><span class="o">.</span><span class="n">aggregation</span><span class="o">.</span><span class="n">StringSummation</span>
+
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">perDayCounts</span><span class="o">></span> <span class="n">insert</span> <span class="n">row1</span> <span class="n">day</span> <span class="mi">20080101</span> <span class="mi">1</span>
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">perDayCounts</span><span class="o">></span> <span class="n">insert</span> <span class="n">row1</span> <span class="n">day</span> <span class="mi">20080101</span> <span class="mi">1</span>
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">perDayCounts</span><span class="o">></span> <span class="n">insert</span> <span class="n">row1</span> <span class="n">day</span> <span class="mi">20080103</span> <span class="mi">1</span>
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">perDayCounts</span><span class="o">></span> <span class="n">insert</span> <span class="n">row2</span> <span class="n">day</span> <span class="mi">20080101</span> <span class="mi">1</span>
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">perDayCounts</span><span class="o">></span> <span class="n">insert</span> <span class="n">row3</span> <span class="n">day</span> <span class="mi">20080101</span> <span class="mi">1</span>
+
+<span class="n">user</span><span class="nv">@myinstance</span> <span class="n">perDayCounts</span><span class="o">></span> <span class="n">scan</span>
+<span class="n">row1</span> <span class="n">day:20080101</span> <span class="o">[]</span> <span class="mi">2</span>
+<span class="n">row1</span> <span class="n">day:20080103</span> <span class="o">[]</span> <span class="mi">1</span>
+<span class="n">row2</span> <span class="n">day:20080101</span> <span class="o">[]</span> <span class="mi">2</span>
+</pre></div>
+
+
+<p>Accumulo includes the following aggregators: </p>
+<ul>
+<li><strong>LongSummation</strong>: expects values of type long and adds them. </li>
+<li><strong>StringSummation</strong>: expects numbers represented as strings and adds them. </li>
+<li><strong>StringMax</strong>: expects numbers as strings and retains the maximum number inserted. </li>
+<li><strong>StringMin</strong>: expects numbers as strings and retains the minimum number inserted. </li>
+</ul>
+<p>Additional Aggregators can be added by creating a Java class that implements <br />
+<strong>org.apache.accumulo.core.iterators.aggregation.Aggregator</strong> and adding a jar containing that class to Accumulo's lib directory. </p>
+<p>An example of an aggregator can be found under <br />
+accumulo/src/examples/main/java/accumulo/examples/aggregation/SortedSetAggregator.java </p>
+<h2 id="a_idpre-splitting_tablesa_pre-splitting_tables"><a id=Pre-splitting_tables></a> Pre-splitting tables</h2>
+<p>Accumulo will balance and distribute tables accross servers. Before a table gets large, it will be maintained as a single tablet on a single server. This limits the speed at which data can be added or queried to the speed of a single node. To improve performance when the a table is new, or small, you can add split points and generate new tablets. </p>
+<p>In the shell: </p>
+<div class="codehilite"><pre><span class="n">root</span><span class="nv">@myinstance</span><span class="o">></span> <span class="n">createtable</span> <span class="n">newTable</span>
+<span class="n">root</span><span class="nv">@myinstance</span><span class="o">></span> <span class="n">addsplits</span> <span class="o">-</span><span class="n">t</span> <span class="n">newTable</span> <span class="n">g</span> <span class="n">n</span> <span class="n">t</span>
+</pre></div>
+
+
+<p>This will create a new table with 4 tablets. The table will be split on the letters <code>g'',</code>n'', and ``t'' which will work nicely if the row data start with lower-case alphabetic characters. If your row data includes binary information or numeric information, or if the distribution of the row information is not flat, then you would pick different split points. Now ingest and query can proceed on 4 nodes which can improve performance. </p>
+<h2 id="a_idmerging_tabletsa_merging_tablets"><a id=Merging_tablets></a> Merging tablets</h2>
+<p>Over time, a table can get very large, so large that it has hundreds of thousands of split points. Once there are enough tablets to spread a table across the entire cluster, additional splits may not improve performance, and may create unnecessary bookkeeping. The distribution of data may change over time. For example, if row data contains date information, and data is continually added and removed to maintain a window of current information, tablets for older rows may be empty. </p>
+<p>Accumulo supports tablet merging, which can be used to reduce delete the number of split points. The following command will merge all rows from <code>A'' to</code>Z'' into a single tablet: </p>
+<div class="codehilite"><pre><span class="n">root</span><span class="nv">@myinstance</span><span class="o">></span> <span class="n">merge</span> <span class="o">-</span><span class="n">t</span> <span class="n">myTable</span> <span class="o">-</span><span class="n">s</span> <span class="n">A</span> <span class="o">-</span><span class="n">e</span> <span class="n">Z</span>
+</pre></div>
+
+
+<p>If the result of a merge produces a tablet that is larger than the configured split size, the tablet may be split by the tablet server. Be sure to increase your tablet size prior to any merges if the goal is to have larger tablets: </p>
+<div class="codehilite"><pre><span class="n">root</span><span class="nv">@myinstance</span><span class="o">></span> <span class="n">config</span> <span class="o">-</span><span class="n">t</span> <span class="n">myTable</span> <span class="o">-</span><span class="n">s</span> <span class="n">table</span><span class="o">.</span><span class="nb">split</span><span class="o">.</span><span class="n">threshold</span><span class="o">=</span><span class="mi">2</span><span class="n">G</span>
+</pre></div>
+
+
+<p>In order to merge small tablets, you can ask accumulo to merge sections of a table smaller than a given size. </p>
+<div class="codehilite"><pre><span class="n">root</span><span class="nv">@myinstance</span><span class="o">></span> <span class="n">merge</span> <span class="o">-</span><span class="n">t</span> <span class="n">myTable</span> <span class="o">-</span><span class="n">s</span> <span class="mi">100</span><span class="n">M</span>
+</pre></div>
+
+
+<p>By default, small tablets will not be merged into tablets that are already larger than the given size. This can leave isolated small tablets. To force small tablets to be merged into larger tablets use the ``-force'' option: </p>
+<div class="codehilite"><pre><span class="n">root</span><span class="nv">@myinstance</span><span class="o">></span> <span class="n">merge</span> <span class="o">-</span><span class="n">t</span> <span class="n">myTable</span> <span class="o">-</span><span class="n">s</span> <span class="mi">100</span><span class="n">M</span> <span class="o">--</span><span class="n">force</span>
+</pre></div>
+
+
+<p>Merging away small tablets works on one section at a time. If your table contains many sections of small split points, or you are attempting to change the split size of the entire table, it will be faster to set the split point and merge the entire table: </p>
+<div class="codehilite"><pre><span class="n">root</span><span class="nv">@myinstance</span><span class="o">></span> <span class="n">config</span> <span class="o">-</span><span class="n">t</span> <span class="n">myTable</span> <span class="o">-</span><span class="n">s</span> <span class="n">table</span><span class="o">.</span><span class="nb">split</span><span class="o">.</span><span class="n">threshold</span><span class="o">=</span><span class="mi">256</span><span class="n">M</span>
+<span class="n">root</span><span class="nv">@myinstance</span><span class="o">></span> <span class="n">merge</span> <span class="o">-</span><span class="n">t</span> <span class="n">myTable</span>
+</pre></div>
+
+
+<h2 id="a_iddelete_rangea_delete_range"><a id=Delete_Range></a> Delete Range</h2>
+<p>Consider an indexing scheme that uses date information in each row. For example ``20110823-15:20:25.013'' might be a row that specifies a date and time. In some cases, we might like to delete rows based on this date, say to remove all the data older than the current year. Accumulo supports a delete range operation which can efficiently removes data between two rows. For example: </p>
+<div class="codehilite"><pre><span class="n">root</span><span class="nv">@myinstance</span><span class="o">></span> <span class="n">deleterange</span> <span class="o">-</span><span class="n">t</span> <span class="n">myTable</span> <span class="o">-</span><span class="n">s</span> <span class="mi">2010</span> <span class="o">-</span><span class="n">e</span> <span class="mi">2011</span>
+</pre></div>
+
+
+<p>This will delete all rows starting with <code>2010'' and it will stop at any row starting</code>2011''. You can delete any data prior to 2011 with: </p>
+<div class="codehilite"><pre><span class="n">root</span><span class="nv">@myinstance</span><span class="o">></span> <span class="n">deleterange</span> <span class="o">-</span><span class="n">t</span> <span class="n">myTable</span> <span class="o">-</span><span class="n">e</span> <span class="mi">2011</span> <span class="o">--</span><span class="n">force</span>
+</pre></div>
+
+
+<p>The shell will not allow you to delete an unbounded range (no start) unless you provide the ``-force'' option. </p>
+<p>Range deletion is implemented using splits at the given start/end positions, and will affect the number of splits in the table. </p>
+<h2 id="a_idcloning_tablesa_cloning_tables"><a id=Cloning_Tables></a> Cloning Tables</h2>
+<p>A new table can be created that points to an existing table's data. This is a very quick metadata operation, no data is actually copied. The cloned table and the source table can change independently after the clone operation. One use case for this feature is testing. For example to test a new filtering iterator, clone the table, add the filter to the clone, and force a major compaction. To perform a test on less data, clone a table and then use delete range to efficiently remove a lot of data from the clone. Another use case is generating a snapshot to guard against human error. To create a snapshot, clone a table and then disable write permissions on the clone. </p>
+<p>The clone operation will point to the source table's files. This is why the flush option is present and is enabled by default in the shell. If the flush option is not enabled, then any data the source table currently has in memory will not exist in the clone. </p>
+<p>A cloned table copies the configuration of the source table. However the permissions of the source table are not copied to the clone. After a clone is created, only the user that created the clone can read and write to it. </p>
+<p>In the following example we see that data inserted after the clone operation is not visible in the clone. </p>
+<div class="codehilite"><pre><span class="n">root</span><span class="nv">@a14</span><span class="o">></span> <span class="n">createtable</span> <span class="n">people</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">people</span><span class="o">></span> <span class="n">insert</span> <span class="mi">890435</span> <span class="n">name</span> <span class="k">last</span> <span class="n">Doe</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">people</span><span class="o">></span> <span class="n">insert</span> <span class="mi">890435</span> <span class="n">name</span> <span class="n">first</span> <span class="n">John</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">people</span><span class="o">></span> <span class="n">clonetable</span> <span class="n">people</span> <span class="n">test</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">people</span><span class="o">></span> <span class="n">insert</span> <span class="mi">890436</span> <span class="n">name</span> <span class="n">first</span> <span class="n">Jane</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">people</span><span class="o">></span> <span class="n">insert</span> <span class="mi">890436</span> <span class="n">name</span> <span class="k">last</span> <span class="n">Doe</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">people</span><span class="o">></span> <span class="n">scan</span>
+<span class="mi">890435</span> <span class="n">name:first</span> <span class="o">[]</span> <span class="n">John</span>
+<span class="mi">890435</span> <span class="n">name:last</span> <span class="o">[]</span> <span class="n">Doe</span>
+<span class="mi">890436</span> <span class="n">name:first</span> <span class="o">[]</span> <span class="n">Jane</span>
+<span class="mi">890436</span> <span class="n">name:last</span> <span class="o">[]</span> <span class="n">Doe</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">people</span><span class="o">></span> <span class="n">table</span> <span class="n">test</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">test</span><span class="o">></span> <span class="n">scan</span>
+<span class="mi">890435</span> <span class="n">name:first</span> <span class="o">[]</span> <span class="n">John</span>
+<span class="mi">890435</span> <span class="n">name:last</span> <span class="o">[]</span> <span class="n">Doe</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">test</span><span class="o">></span>
+</pre></div>
+
+
+<p>The du command in the shell shows how much space a table is using in HDFS. This command can also show how much overlapping space two cloned tables have in HDFS. In the example below du shows table ci is using 428M. Then ci is cloned to cic and du shows that both tables share 428M. After three entries are inserted into cic and its flushed, du shows the two tables still share 428M but cic has 226 bytes to itself. Finally, table cic is compacted and then du shows that each table uses 428M. </p>
+<div class="codehilite"><pre><span class="n">root</span><span class="nv">@a14</span><span class="o">></span> <span class="n">du</span> <span class="n">ci</span>
+ <span class="mi">428</span><span class="p">,</span><span class="mi">482</span><span class="p">,</span><span class="mi">573</span> <span class="p">[</span><span class="n">ci</span><span class="p">]</span>
+<span class="n">root</span><span class="nv">@a14</span><span class="o">></span> <span class="n">clonetable</span> <span class="n">ci</span> <span class="n">cic</span>
+<span class="n">root</span><span class="nv">@a14</span><span class="o">></span> <span class="n">du</span> <span class="n">ci</span> <span class="n">cic</span>
+ <span class="mi">428</span><span class="p">,</span><span class="mi">482</span><span class="p">,</span><span class="mi">573</span> <span class="p">[</span><span class="n">ci</span><span class="p">,</span> <span class="n">cic</span><span class="p">]</span>
+<span class="n">root</span><span class="nv">@a14</span><span class="o">></span> <span class="n">table</span> <span class="n">cic</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">cic</span><span class="o">></span> <span class="n">insert</span> <span class="n">r1</span> <span class="n">cf1</span> <span class="n">cq1</span> <span class="n">v1</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">cic</span><span class="o">></span> <span class="n">insert</span> <span class="n">r1</span> <span class="n">cf1</span> <span class="n">cq2</span> <span class="n">v2</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">cic</span><span class="o">></span> <span class="n">insert</span> <span class="n">r1</span> <span class="n">cf1</span> <span class="n">cq3</span> <span class="n">v3</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">cic</span><span class="o">></span> <span class="n">flush</span> <span class="o">-</span><span class="n">t</span> <span class="n">cic</span> <span class="o">-</span><span class="n">w</span>
+<span class="mi">27</span> <span class="mi">15</span><span class="p">:</span><span class="mo">00</span><span class="p">:</span><span class="mi">13</span><span class="p">,</span><span class="mi">908</span> <span class="p">[</span><span class="n">shell</span><span class="o">.</span><span class="n">Shell</span><span class="p">]</span> <span class="n">INFO</span> <span class="p">:</span> <span class="n">Flush</span> <span class="n">of</span> <span class="n">table</span> <span class="n">cic</span> <span class="n">completed</span><span class="o">.</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">cic</span><span class="o">></span> <span class="n">du</span> <span class="n">ci</span> <span class="n">cic</span>
+ <span class="mi">428</span><span class="p">,</span><span class="mi">482</span><span class="p">,</span><span class="mi">573</span> <span class="p">[</span><span class="n">ci</span><span class="p">,</span> <span class="n">cic</span><span class="p">]</span>
+ <span class="mi">226</span> <span class="p">[</span><span class="n">cic</span><span class="p">]</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">cic</span><span class="o">></span> <span class="n">compact</span> <span class="o">-</span><span class="n">t</span> <span class="n">cic</span> <span class="o">-</span><span class="n">w</span>
+<span class="mi">27</span> <span class="mi">15</span><span class="p">:</span><span class="mo">00</span><span class="p">:</span><span class="mi">35</span><span class="p">,</span><span class="mi">871</span> <span class="p">[</span><span class="n">shell</span><span class="o">.</span><span class="n">Shell</span><span class="p">]</span> <span class="n">INFO</span> <span class="p">:</span> <span class="n">Compacting</span> <span class="n">table</span> <span class="o">...</span>
+<span class="mi">27</span> <span class="mi">15</span><span class="p">:</span><span class="mo">03</span><span class="p">:</span><span class="mo">03</span><span class="p">,</span><span class="mi">303</span> <span class="p">[</span><span class="n">shell</span><span class="o">.</span><span class="n">Shell</span><span class="p">]</span> <span class="n">INFO</span> <span class="p">:</span> <span class="n">Compaction</span> <span class="n">of</span> <span class="n">table</span> <span class="n">cic</span> <span class="n">completed</span> <span class="k">for</span> <span class="n">given</span> <span class="n">range</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">cic</span><span class="o">></span> <span class="n">du</span> <span class="n">ci</span> <span class="n">cic</span>
+ <span class="mi">428</span><span class="p">,</span><span class="mi">482</span><span class="p">,</span><span class="mi">573</span> <span class="p">[</span><span class="n">ci</span><span class="p">]</span>
+ <span class="mi">428</span><span class="p">,</span><span class="mi">482</span><span class="p">,</span><span class="mi">612</span> <span class="p">[</span><span class="n">cic</span><span class="p">]</span>
+<span class="n">root</span><span class="nv">@a14</span> <span class="n">cic</span><span class="o">></span>
+</pre></div>
+
+
+<hr />
+<p><strong> Next:</strong> <a href="Table_Design.html">Table Design</a> <strong> Up:</strong> <a href="accumulo_user_manual.html">Accumulo User Manual Version 1.4</a> <strong> Previous:</strong> <a href="Writing_Accumulo_Clients.html">Writing Accumulo Clients</a> <strong> <a href="Contents.html">Contents</a></strong></p>
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+ <h1 class="title">Accumulo User Manual: Table Design</h1>
+ <p><strong> Next:</strong> <a href="High_Speed_Ingest.html">High-Speed Ingest</a> <strong> Up:</strong> <a href="accumulo_user_manual.html">Accumulo User Manual Version 1.4</a> <strong> Previous:</strong> <a href="Table_Configuration.html">Table Configuration</a> <strong> <a href="Contents.html">Contents</a></strong> <br />
+</p>
+<p><a id=CHILD_LINKS></a><strong>Subsections</strong></p>
+<ul>
+<li><a href="Table_Design.html#Basic_Table">Basic Table</a></li>
+<li><a href="Table_Design.html#RowID_Design">RowID Design</a></li>
+<li><a href="Table_Design.html#Indexing">Indexing</a></li>
+<li><a href="Table_Design.html#Entity-Attribute_and_Graph_Tables">Entity-Attribute and Graph Tables</a></li>
+<li><a href="Table_Design.html#Document-Partitioned_Indexing">Document-Partitioned Indexing</a></li>
+</ul>
+<hr />
+<h2 id="a_idtable_designa_table_design"><a id=Table_Design></a> Table Design</h2>
+<h2 id="a_idbasic_tablea_basic_table"><a id=Basic_Table></a> Basic Table</h2>
+<p>Since Accumulo tables are sorted by row ID, each table can be thought of as being indexed by the row ID. Lookups performed row ID can be executed quickly, by doing a binary search, first across the tablets, and then within a tablet. Clients should choose a row ID carefully in order to support their desired application. A simple rule is to select a unique identifier as the row ID for each entity to be stored and assign all the other attributes to be tracked to be columns under this row ID. For example, if we have the following data in a comma-separated file: </p>
+<div class="codehilite"><pre> <span class="n">userid</span><span class="p">,</span><span class="n">age</span><span class="p">,</span><span class="n">address</span><span class="p">,</span><span class="n">account</span><span class="o">-</span><span class="n">balance</span>
+</pre></div>
+
+
+<p>We might choose to store this data using the userid as the rowID and the rest of the data in column families: </p>
+<div class="codehilite"><pre><span class="n">Mutation</span> <span class="n">m</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Mutation</span><span class="p">(</span><span class="k">new</span> <span class="n">Text</span><span class="p">(</span><span class="n">userid</span><span class="p">));</span>
+<span class="n">m</span><span class="o">.</span><span class="n">put</span><span class="p">(</span><span class="k">new</span> <span class="n">Text</span><span class="p">(</span><span class="s">"age"</span><span class="p">),</span> <span class="n">age</span><span class="p">);</span>
+<span class="n">m</span><span class="o">.</span><span class="n">put</span><span class="p">(</span><span class="k">new</span> <span class="n">Text</span><span class="p">(</span><span class="s">"address"</span><span class="p">),</span> <span class="n">address</span><span class="p">);</span>
+<span class="n">m</span><span class="o">.</span><span class="n">put</span><span class="p">(</span><span class="k">new</span> <span class="n">Text</span><span class="p">(</span><span class="s">"balance"</span><span class="p">),</span> <span class="n">account_balance</span><span class="p">);</span>
+
+<span class="n">writer</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">m</span><span class="p">);</span>
+</pre></div>
+
+
+<p>We could then retrieve any of the columns for a specific userid by specifying the userid as the range of a scanner and fetching specific columns: </p>
+<div class="codehilite"><pre><span class="n">Range</span> <span class="n">r</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Range</span><span class="p">(</span><span class="n">userid</span><span class="p">,</span> <span class="n">userid</span><span class="p">);</span> <span class="sr">//</span> <span class="n">single</span> <span class="n">row</span>
+<span class="n">Scanner</span> <span class="n">s</span> <span class="o">=</span> <span class="n">conn</span><span class="o">.</span><span class="n">createScanner</span><span class="p">(</span><span class="s">"userdata"</span><span class="p">,</span> <span class="n">auths</span><span class="p">);</span>
+<span class="n">s</span><span class="o">.</span><span class="n">setRange</span><span class="p">(</span><span class="n">r</span><span class="p">);</span>
+<span class="n">s</span><span class="o">.</span><span class="n">fetchColumnFamily</span><span class="p">(</span><span class="k">new</span> <span class="n">Text</span><span class="p">(</span><span class="s">"age"</span><span class="p">));</span>
+
+<span class="k">for</span><span class="p">(</span><span class="n">Entry</span><span class="sr"><Key,Value></span> <span class="n">entry</span> <span class="p">:</span> <span class="n">s</span><span class="p">)</span>
+ <span class="n">System</span><span class="o">.</span><span class="n">out</span><span class="o">.</span><span class="n">println</span><span class="p">(</span><span class="n">entry</span><span class="o">.</span><span class="n">getValue</span><span class="p">()</span><span class="o">.</span><span class="n">toString</span><span class="p">());</span>
+</pre></div>
+
+
+<h2 id="a_idrowid_designa_rowid_design"><a id=RowID_Design></a> RowID Design</h2>
+<p>Often it is necessary to transform the rowID in order to have rows ordered in a way that is optimal for anticipated access patterns. A good example of this is reversing the order of components of internet domain names in order to group rows of the same parent domain together: </p>
+<div class="codehilite"><pre><span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">code</span>
+<span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">labs</span>
+<span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">mail</span>
+<span class="n">com</span><span class="o">.</span><span class="n">yahoo</span><span class="o">.</span><span class="n">mail</span>
+<span class="n">com</span><span class="o">.</span><span class="n">yahoo</span><span class="o">.</span><span class="n">research</span>
+</pre></div>
+
+
+<p>Some data may result in the creation of very large rows - rows with many columns. In this case the table designer may wish to split up these rows for better load balancing while keeping them sorted together for scanning purposes. This can be done by appending a random substring at the end of the row: </p>
+<div class="codehilite"><pre><span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">code_00</span>
+<span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">code_01</span>
+<span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">code_02</span>
+<span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">labs_00</span>
+<span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">mail_00</span>
+<span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">mail_01</span>
+</pre></div>
+
+
+<p>It could also be done by adding a string representation of some period of time such as date to the week or month: </p>
+<div class="codehilite"><pre><span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">code_201003</span>
+<span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">code_201004</span>
+<span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">code_201005</span>
+<span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">labs_201003</span>
+<span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">mail_201003</span>
+<span class="n">com</span><span class="o">.</span><span class="n">google</span><span class="o">.</span><span class="n">mail_201004</span>
+</pre></div>
+
+
+<p>Appending dates provides the additional capability of restricting a scan to a given date range. </p>
+<h2 id="a_idindexinga_indexing"><a id=Indexing></a> Indexing</h2>
+<p>In order to support lookups via more than one attribute of an entity, additional indexes can be built. However, because Accumulo tables can support any number of columns without specifying them beforehand, a single additional index will often suffice for supporting lookups of records in the main table. Here, the index has, as the rowID, the Value or Term from the main table, the column families are the same, and the column qualifier of the index table contains the rowID from the main table. </p>
+<p><img alt="converted table" src="img2.png" /></p>
+<p>Note: We store rowIDs in the column qualifier rather than the Value so that we can have more than one rowID associated with a particular term within the index. If we stored this in the Value we would only see one of the rows in which the value appears since Accumulo is configured by default to return the one most recent value associated with a key. </p>
+<p>Lookups can then be done by scanning the Index Table first for occurrences of the desired values in the columns specified, which returns a list of row ID from the main table. These can then be used to retrieve each matching record, in their entirety, or a subset of their columns, from the Main Table. </p>
+<p>To support efficient lookups of multiple rowIDs from the same table, the Accumulo client library provides a BatchScanner. Users specify a set of Ranges to the BatchScanner, which performs the lookups in multiple threads to multiple servers and returns an Iterator over all the rows retrieved. The rows returned are NOT in sorted order, as is the case with the basic Scanner interface. </p>
+<div class="codehilite"><pre><span class="sr">//</span> <span class="n">first</span> <span class="n">we</span> <span class="n">scan</span> <span class="n">the</span> <span class="nb">index</span> <span class="k">for</span> <span class="n">IDs</span> <span class="n">of</span> <span class="n">rows</span> <span class="n">matching</span> <span class="k">our</span> <span class="n">query</span>
+
+<span class="n">Text</span> <span class="n">term</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Text</span><span class="p">(</span><span class="s">"mySearchTerm"</span><span class="p">);</span>
+
+<span class="n">HashSet</span><span class="sr"><Text></span> <span class="n">matchingRows</span> <span class="o">=</span> <span class="k">new</span> <span class="n">HashSet</span><span class="sr"><Text></span><span class="p">();</span>
+
+<span class="n">Scanner</span> <span class="n">indexScanner</span> <span class="o">=</span> <span class="n">createScanner</span><span class="p">(</span><span class="s">"index"</span><span class="p">,</span> <span class="n">auths</span><span class="p">);</span>
+<span class="n">indexScanner</span><span class="o">.</span><span class="n">setRange</span><span class="p">(</span><span class="k">new</span> <span class="n">Range</span><span class="p">(</span><span class="n">term</span><span class="p">,</span> <span class="n">term</span><span class="p">));</span>
+
+<span class="sr">//</span> <span class="n">we</span> <span class="n">retrieve</span> <span class="n">the</span> <span class="n">matching</span> <span class="n">rowIDs</span> <span class="ow">and</span> <span class="n">create</span> <span class="n">a</span> <span class="n">set</span> <span class="n">of</span> <span class="n">ranges</span>
+<span class="k">for</span><span class="p">(</span><span class="n">Entry</span><span class="sr"><Key,Value></span> <span class="n">entry</span> <span class="p">:</span> <span class="n">indexScanner</span><span class="p">)</span>
+ <span class="n">matchingRows</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="k">new</span> <span class="n">Text</span><span class="p">(</span><span class="n">entry</span><span class="o">.</span><span class="n">getValue</span><span class="p">()));</span>
+
+<span class="sr">//</span> <span class="n">now</span> <span class="n">we</span> <span class="n">pass</span> <span class="n">the</span> <span class="n">set</span> <span class="n">of</span> <span class="n">rowIDs</span> <span class="n">to</span> <span class="n">the</span> <span class="n">batch</span> <span class="n">scanner</span> <span class="n">to</span> <span class="n">retrieve</span> <span class="n">them</span>
+<span class="n">BatchScanner</span> <span class="n">bscan</span> <span class="o">=</span> <span class="n">conn</span><span class="o">.</span><span class="n">createBatchScanner</span><span class="p">(</span><span class="s">"table"</span><span class="p">,</span> <span class="n">auths</span><span class="p">,</span> <span class="mi">10</span><span class="p">);</span>
+
+<span class="n">bscan</span><span class="o">.</span><span class="n">setRanges</span><span class="p">(</span><span class="n">matchingRows</span><span class="p">);</span>
+<span class="n">bscan</span><span class="o">.</span><span class="n">fetchFamily</span><span class="p">(</span><span class="s">"attributes"</span><span class="p">);</span>
+
+<span class="k">for</span><span class="p">(</span><span class="n">Entry</span><span class="sr"><Key,Value></span> <span class="n">entry</span> <span class="p">:</span> <span class="n">scan</span><span class="p">)</span>
+ <span class="n">System</span><span class="o">.</span><span class="n">out</span><span class="o">.</span><span class="n">println</span><span class="p">(</span><span class="n">e</span><span class="o">.</span><span class="n">getValue</span><span class="p">());</span>
+</pre></div>
+
+
+<p>One advantage of the dynamic schema capabilities of Accumulo is that different fields may be indexed into the same physical table. However, it may be necessary to create different index tables if the terms must be formatted differently in order to maintain proper sort order. For example, real numbers must be formatted differently than their usual notation in order to be sorted correctly. In these cases, usually one index per unique data type will suffice. </p>
+<h2 id="a_identity-attribute_and_graph_tablesa_entity-attribute_and_graph_tables"><a id=Entity-Attribute_and_Graph_Tables></a> Entity-Attribute and Graph Tables</h2>
+<p>Accumulo is ideal for storing entities and their attributes, especially of the attributes are sparse. It is often useful to join several datasets together on common entities within the same table. This can allow for the representation of graphs, including nodes, their attributes, and connections to other nodes. </p>
+<p>Rather than storing individual events, Entity-Attribute or Graph tables store aggregate information about the entities involved in the events and the relationships between entities. This is often preferrable when single events aren't very useful and when a continuously updated summarization is desired. </p>
+<p>The physical schema for an entity-attribute or graph table is as follows: </p>
+<p><img alt="converted table" src="img3.png" /></p>
+<p>For example, to keep track of employees, managers and products the following entity-attribute table could be used. Note that the weights are not always necessary and are set to 0 when not used. </p>
+<p><img alt="converted table" src="img4.png" /> <br />
+</p>
+<p>To allow efficient updating of edge weights, an aggregating iterator can be configured to add the value of all mutations applied with the same key. These types of tables can easily be created from raw events by simply extracting the entities, attributes, and relationships from individual events and inserting the keys into Accumulo each with a count of 1. The aggregating iterator will take care of maintaining the edge weights. </p>
+<h2 id="a_iddocument-partitioned_indexinga_document-partitioned_indexing"><a id=Document-Partitioned_Indexing></a> Document-Partitioned Indexing</h2>
+<p>Using a simple index as described above works well when looking for records that match one of a set of given criteria. When looking for records that match more than one criterion simultaneously, such as when looking for documents that contain all of the words <code>the' and</code>white' and `house', there are several issues. </p>
+<p>First is that the set of all records matching any one of the search terms must be sent to the client, which incurs a lot of network traffic. The second problem is that the client is responsible for performing set intersection on the sets of records returned to eliminate all but the records matching all search terms. The memory of the client may easily be overwhelmed during this operation. </p>
+<p>For these reasons Accumulo includes support for a scheme known as sharded indexing, in which these set operations can be performed at the TabletServers and decisions about which records to include in the result set can be made without incurring network traffic. </p>
+<p>This is accomplished via partitioning records into bins that each reside on at most one TabletServer, and then creating an index of terms per record within each bin as follows: </p>
+<p><img alt="converted table" src="img5.png" /></p>
+<p>Documents or records are mapped into bins by a user-defined ingest application. By storing the BinID as the RowID we ensure that all the information for a particular bin is contained in a single tablet and hosted on a single TabletServer since Accumulo never splits rows across tablets. Storing the Terms as column families serves to enable fast lookups of all the documents within this bin that contain the given term. </p>
+<p>Finally, we perform set intersection operations on the TabletServer via a special iterator called the Intersecting Iterator. Since documents are partitioned into many bins, a search of all documents must search every bin. We can use the BatchScanner to scan all bins in parallel. The Intersecting Iterator should be enabled on a BatchScanner within user query code as follows: </p>
+<div class="codehilite"><pre><span class="n">Text</span><span class="o">[]</span> <span class="n">terms</span> <span class="o">=</span> <span class="p">{</span><span class="k">new</span> <span class="n">Text</span><span class="p">(</span><span class="s">"the"</span><span class="p">),</span> <span class="k">new</span> <span class="n">Text</span><span class="p">(</span><span class="s">"white"</span><span class="p">),</span> <span class="k">new</span> <span class="n">Text</span><span class="p">(</span><span class="s">"house"</span><span class="p">)};</span>
+
+<span class="n">BatchScanner</span> <span class="n">bs</span> <span class="o">=</span> <span class="n">conn</span><span class="o">.</span><span class="n">createBatchScanner</span><span class="p">(</span><span class="n">table</span><span class="p">,</span> <span class="n">auths</span><span class="p">,</span> <span class="mi">20</span><span class="p">);</span>
+<span class="n">IteratorSetting</span> <span class="n">iter</span> <span class="o">=</span> <span class="k">new</span> <span class="n">IteratorSetting</span><span class="p">(</span><span class="mi">20</span><span class="p">,</span> <span class="s">"ii"</span><span class="p">,</span> <span class="n">IntersectingIterator</span><span class="o">.</span><span class="n">class</span><span class="p">);</span>
+<span class="n">IntersectingIterator</span><span class="o">.</span><span class="n">setColumnFamilies</span><span class="p">(</span><span class="n">iter</span><span class="p">,</span> <span class="n">terms</span><span class="p">);</span>
+<span class="n">bs</span><span class="o">.</span><span class="n">addScanIterator</span><span class="p">(</span><span class="n">iter</span><span class="p">);</span>
+<span class="n">bs</span><span class="o">.</span><span class="n">setRanges</span><span class="p">(</span><span class="n">Collections</span><span class="o">.</span><span class="n">singleton</span><span class="p">(</span><span class="k">new</span> <span class="n">Range</span><span class="p">()));</span>
+
+<span class="k">for</span><span class="p">(</span><span class="n">Entry</span><span class="sr"><Key,Value></span> <span class="n">entry</span> <span class="p">:</span> <span class="n">bs</span><span class="p">)</span> <span class="p">{</span>
+ <span class="n">System</span><span class="o">.</span><span class="n">out</span><span class="o">.</span><span class="n">println</span><span class="p">(</span><span class="s">" "</span> <span class="o">+</span> <span class="n">entry</span><span class="o">.</span><span class="n">getKey</span><span class="p">()</span><span class="o">.</span><span class="n">getColumnQualifier</span><span class="p">());</span>
+<span class="p">}</span>
+</pre></div>
+
+
+<p>This code effectively has the BatchScanner scan all tablets of a table, looking for documents that match all the given terms. Because all tablets are being scanned for every query, each query is more expensive than other Accumulo scans, which typically involve a small number of TabletServers. This reduces the number of concurrent queries supported and is subject to what is known as the `straggler' problem in which every query runs as slow as the slowest server participating. </p>
+<p>Of course, fast servers will return their results to the client which can display them to the user immediately while they wait for the rest of the results to arrive. If the results are unordered this is quite effective as the first results to arrive are as good as any others to the user. </p>
+<hr />
+<p><strong> Next:</strong> <a href="High_Speed_Ingest.html">High-Speed Ingest</a> <strong> Up:</strong> <a href="accumulo_user_manual.html">Accumulo User Manual Version 1.4</a> <strong> Previous:</strong> <a href="Table_Configuration.html">Table Configuration</a> <strong> <a href="Contents.html">Contents</a></strong></p>
+ </div>
+
+ <div id="footer">
+ <div class="copyright">
+ <p>
+ Copyright © 2011 The Apache Software Foundation, Licensed under
+ the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.
+ <br />
+ Apache and the Apache feather logos are trademarks of The Apache Software Foundation.
+ </p>
+ </div>
+ <a alt="Apache Incubator" href="http://incubator.apache.org">
+ <img id="asf-logo" alt="Apache Incubator" src="/accumulo/images/apache-incubator-logo.png" width="150"/>
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