| --- |
| layout: docpage |
| |
| title: "Documentation" |
| |
| is_homepage: false |
| is_sphinx_doc: true |
| |
| doc-parent: "Architecture" |
| |
| doc-title: "Overview" |
| doc-header-links: ' |
| <link rel="top" title="Apache Cassandra Documentation v4.0-rc1" href="../index.html"/> |
| <link rel="up" title="Architecture" href="index.html"/> |
| <link rel="next" title="Dynamo" href="dynamo.html"/> |
| <link rel="prev" title="Architecture" href="index.html"/> |
| ' |
| doc-search-path: "../search.html" |
| |
| extra-footer: ' |
| <script type="text/javascript"> |
| var DOCUMENTATION_OPTIONS = { |
| URL_ROOT: "", |
| VERSION: "", |
| COLLAPSE_INDEX: false, |
| FILE_SUFFIX: ".html", |
| HAS_SOURCE: false, |
| SOURCELINK_SUFFIX: ".txt" |
| }; |
| </script> |
| ' |
| |
| --- |
| <div class="container-fluid"> |
| <div class="row"> |
| <div class="col-md-3"> |
| <div class="doc-navigation"> |
| <div class="doc-menu" role="navigation"> |
| <div class="navbar-header"> |
| <button type="button" class="pull-left navbar-toggle" data-toggle="collapse" data-target=".sidebar-navbar-collapse"> |
| <span class="sr-only">Toggle navigation</span> |
| <span class="icon-bar"></span> |
| <span class="icon-bar"></span> |
| <span class="icon-bar"></span> |
| </button> |
| </div> |
| <div class="navbar-collapse collapse sidebar-navbar-collapse"> |
| <form id="doc-search-form" class="navbar-form" action="../search.html" method="get" role="search"> |
| <div class="form-group"> |
| <input type="text" size="30" class="form-control input-sm" name="q" placeholder="Search docs"> |
| <input type="hidden" name="check_keywords" value="yes" /> |
| <input type="hidden" name="area" value="default" /> |
| </div> |
| </form> |
| |
| |
| |
| <ul class="current"> |
| <li class="toctree-l1"><a class="reference internal" href="../getting_started/index.html">Getting Started</a></li> |
| <li class="toctree-l1"><a class="reference internal" href="../new/index.html">New Features in Apache Cassandra 4.0</a></li> |
| <li class="toctree-l1 current"><a class="reference internal" href="index.html">Architecture</a><ul class="current"> |
| <li class="toctree-l2 current"><a class="current reference internal" href="#">Overview</a><ul> |
| <li class="toctree-l3"><a class="reference internal" href="#features">Features</a></li> |
| <li class="toctree-l3"><a class="reference internal" href="#operating">Operating</a></li> |
| </ul> |
| </li> |
| <li class="toctree-l2"><a class="reference internal" href="dynamo.html">Dynamo</a></li> |
| <li class="toctree-l2"><a class="reference internal" href="storage_engine.html">Storage Engine</a></li> |
| <li class="toctree-l2"><a class="reference internal" href="guarantees.html">Guarantees</a></li> |
| </ul> |
| </li> |
| <li class="toctree-l1"><a class="reference internal" href="../cql/index.html">The Cassandra Query Language (CQL)</a></li> |
| <li class="toctree-l1"><a class="reference internal" href="../data_modeling/index.html">Data Modeling</a></li> |
| <li class="toctree-l1"><a class="reference internal" href="../configuration/index.html">Configuring Cassandra</a></li> |
| <li class="toctree-l1"><a class="reference internal" href="../operating/index.html">Operating Cassandra</a></li> |
| <li class="toctree-l1"><a class="reference internal" href="../tools/index.html">Cassandra Tools</a></li> |
| <li class="toctree-l1"><a class="reference internal" href="../troubleshooting/index.html">Troubleshooting</a></li> |
| <li class="toctree-l1"><a class="reference internal" href="../development/index.html">Contributing to Cassandra</a></li> |
| <li class="toctree-l1"><a class="reference internal" href="../faq/index.html">Frequently Asked Questions</a></li> |
| <li class="toctree-l1"><a class="reference internal" href="../plugins/index.html">Third-Party Plugins</a></li> |
| <li class="toctree-l1"><a class="reference internal" href="../bugs.html">Reporting Bugs</a></li> |
| <li class="toctree-l1"><a class="reference internal" href="../contactus.html">Contact us</a></li> |
| </ul> |
| |
| |
| |
| </div><!--/.nav-collapse --> |
| </div> |
| </div> |
| </div> |
| <div class="col-md-8"> |
| <div class="content doc-content"> |
| <div class="content-container"> |
| |
| <div class="section" id="overview"> |
| <span id="id1"></span><h1>Overview<a class="headerlink" href="#overview" title="Permalink to this headline">¶</a></h1> |
| <p>Apache Cassandra is an open source, distributed, NoSQL database. It presents |
| a partitioned wide column storage model with eventually consistent semantics.</p> |
| <p>Apache Cassandra was initially designed at <a class="reference external" href="https://www.cs.cornell.edu/projects/ladis2009/papers/lakshman-ladis2009.pdf">Facebook</a> |
| using a staged event-driven architecture (<a class="reference external" href="http://www.sosp.org/2001/papers/welsh.pdf">SEDA</a>) to implement a combination of |
| Amazon’s <a class="reference external" href="http://courses.cse.tamu.edu/caverlee/csce438/readings/dynamo-paper.pdf">Dynamo</a> |
| distributed storage and replication techniques combined with Google’s <a class="reference external" href="https://static.googleusercontent.com/media/research.google.com/en//archive/bigtable-osdi06.pdf">Bigtable</a> |
| data and storage engine model. Dynamo and Bigtable were both developed to meet |
| emerging requirements for scalable, reliable and highly available storage |
| systems, but each had areas that could be improved.</p> |
| <p>Cassandra was designed as a best in class combination of both systems to meet |
| emerging large scale, both in data footprint and query volume, storage |
| requirements. As applications began to require full global replication and |
| always available low-latency reads and writes, it became imperative to design a |
| new kind of database model as the relational database systems of the time |
| struggled to meet the new requirements of global scale applications.</p> |
| <p>Systems like Cassandra are designed for these challenges and seek the |
| following design objectives:</p> |
| <ul class="simple"> |
| <li>Full multi-master database replication</li> |
| <li>Global availability at low latency</li> |
| <li>Scaling out on commodity hardware</li> |
| <li>Linear throughput increase with each additional processor</li> |
| <li>Online load balancing and cluster growth</li> |
| <li>Partitioned key-oriented queries</li> |
| <li>Flexible schema</li> |
| </ul> |
| <div class="section" id="features"> |
| <h2>Features<a class="headerlink" href="#features" title="Permalink to this headline">¶</a></h2> |
| <p>Cassandra provides the Cassandra Query Language (CQL), an SQL-like language, |
| to create and update database schema and access data. CQL allows users to |
| organize data within a cluster of Cassandra nodes using:</p> |
| <ul class="simple"> |
| <li><strong>Keyspace</strong>: defines how a dataset is replicated, for example in which |
| datacenters and how many copies. Keyspaces contain tables.</li> |
| <li><strong>Table</strong>: defines the typed schema for a collection of partitions. Cassandra |
| tables have flexible addition of new columns to tables with zero downtime. |
| Tables contain partitions, which contain partitions, which contain columns.</li> |
| <li><strong>Partition</strong>: defines the mandatory part of the primary key all rows in |
| Cassandra must have. All performant queries supply the partition key in |
| the query.</li> |
| <li><strong>Row</strong>: contains a collection of columns identified by a unique primary key |
| made up of the partition key and optionally additional clustering keys.</li> |
| <li><strong>Column</strong>: A single datum with a type which belong to a row.</li> |
| </ul> |
| <p>CQL supports numerous advanced features over a partitioned dataset such as:</p> |
| <ul class="simple"> |
| <li>Single partition lightweight transactions with atomic compare and set |
| semantics.</li> |
| <li>User-defined types, functions and aggregates</li> |
| <li>Collection types including sets, maps, and lists.</li> |
| <li>Local secondary indices</li> |
| <li>(Experimental) materialized views</li> |
| </ul> |
| <p>Cassandra explicitly chooses not to implement operations that require cross |
| partition coordination as they are typically slow and hard to provide highly |
| available global semantics. For example Cassandra does not support:</p> |
| <ul class="simple"> |
| <li>Cross partition transactions</li> |
| <li>Distributed joins</li> |
| <li>Foreign keys or referential integrity.</li> |
| </ul> |
| </div> |
| <div class="section" id="operating"> |
| <h2>Operating<a class="headerlink" href="#operating" title="Permalink to this headline">¶</a></h2> |
| <p>Apache Cassandra configuration settings are configured in the <code class="docutils literal notranslate"><span class="pre">cassandra.yaml</span></code> |
| file that can be edited by hand or with the aid of configuration management tools. |
| Some settings can be manipulated live using an online interface, but others |
| require a restart of the database to take effect.</p> |
| <p>Cassandra provides tools for managing a cluster. The <code class="docutils literal notranslate"><span class="pre">nodetool</span></code> command |
| interacts with Cassandra’s live control interface, allowing runtime manipulation |
| of many settings from <code class="docutils literal notranslate"><span class="pre">cassandra.yaml</span></code>. The <code class="docutils literal notranslate"><span class="pre">auditlogviewer</span></code> is used |
| to view the audit logs. The <code class="docutils literal notranslate"><span class="pre">fqltool</span></code> is used to view, replay and compare |
| full query logs. The <code class="docutils literal notranslate"><span class="pre">auditlogviewer</span></code> and <code class="docutils literal notranslate"><span class="pre">fqltool</span></code> are new tools in |
| Apache Cassandra 4.0.</p> |
| <p>In addition, Cassandra supports out of the box atomic snapshot functionality, |
| which presents a point in time snapshot of Cassandra’s data for easy |
| integration with many backup tools. Cassandra also supports incremental backups |
| where data can be backed up as it is written.</p> |
| <p>Apache Cassandra 4.0 has added several new features including virtual tables. |
| transient replication, audit logging, full query logging, and support for Java |
| 11. Two of these features are experimental: transient replication and Java 11 |
| support.</p> |
| </div> |
| </div> |
| |
| |
| |
| |
| <div class="doc-prev-next-links" role="navigation" aria-label="footer navigation"> |
| |
| <a href="dynamo.html" class="btn btn-default pull-right " role="button" title="Dynamo" accesskey="n">Next <span class="glyphicon glyphicon-circle-arrow-right" aria-hidden="true"></span></a> |
| |
| |
| <a href="index.html" class="btn btn-default" role="button" title="Architecture" accesskey="p"><span class="glyphicon glyphicon-circle-arrow-left" aria-hidden="true"></span> Previous</a> |
| |
| </div> |
| |
| </div> |
| </div> |
| </div> |
| </div> |
| </div> |