| --- |
| layout: docpage |
| |
| title: "Documentation" |
| |
| is_homepage: false |
| is_sphinx_doc: true |
| |
| doc-title: "Size Tiered Compaction Strategy" |
| doc-header-links: ' |
| <link rel="top" title="Apache Cassandra Documentation v4.0-rc1" 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> |
| <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"><a class="reference internal" href="../../architecture/index.html">Architecture</a></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="../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="size-tiered-compaction-strategy"> |
| <span id="stcs"></span><h1>Size Tiered Compaction Strategy<a class="headerlink" href="#size-tiered-compaction-strategy" title="Permalink to this headline">¶</a></h1> |
| <p>The basic idea of <code class="docutils literal notranslate"><span class="pre">SizeTieredCompactionStrategy</span></code> (STCS) is to merge sstables of approximately the same size. All |
| sstables are put in different buckets depending on their size. An sstable is added to the bucket if size of the sstable |
| is within <code class="docutils literal notranslate"><span class="pre">bucket_low</span></code> and <code class="docutils literal notranslate"><span class="pre">bucket_high</span></code> of the current average size of the sstables already in the bucket. This |
| will create several buckets and the most interesting of those buckets will be compacted. The most interesting one is |
| decided by figuring out which bucket’s sstables takes the most reads.</p> |
| <div class="section" id="major-compaction"> |
| <h2>Major compaction<a class="headerlink" href="#major-compaction" title="Permalink to this headline">¶</a></h2> |
| <p>When running a major compaction with STCS you will end up with two sstables per data directory (one for repaired data |
| and one for unrepaired data). There is also an option (-s) to do a major compaction that splits the output into several |
| sstables. The sizes of the sstables are approximately 50%, 25%, 12.5%… of the total size.</p> |
| </div> |
| <div class="section" id="stcs-options"> |
| <span id="id1"></span><h2>STCS options<a class="headerlink" href="#stcs-options" title="Permalink to this headline">¶</a></h2> |
| <dl class="docutils"> |
| <dt><code class="docutils literal notranslate"><span class="pre">min_sstable_size</span></code> (default: 50MB)</dt> |
| <dd>Sstables smaller than this are put in the same bucket.</dd> |
| <dt><code class="docutils literal notranslate"><span class="pre">bucket_low</span></code> (default: 0.5)</dt> |
| <dd>How much smaller than the average size of a bucket a sstable should be before not being included in the bucket. That |
| is, if <code class="docutils literal notranslate"><span class="pre">bucket_low</span> <span class="pre">*</span> <span class="pre">avg_bucket_size</span> <span class="pre"><</span> <span class="pre">sstable_size</span></code> (and the <code class="docutils literal notranslate"><span class="pre">bucket_high</span></code> condition holds, see below), then |
| the sstable is added to the bucket.</dd> |
| <dt><code class="docutils literal notranslate"><span class="pre">bucket_high</span></code> (default: 1.5)</dt> |
| <dd>How much bigger than the average size of a bucket a sstable should be before not being included in the bucket. That |
| is, if <code class="docutils literal notranslate"><span class="pre">sstable_size</span> <span class="pre"><</span> <span class="pre">bucket_high</span> <span class="pre">*</span> <span class="pre">avg_bucket_size</span></code> (and the <code class="docutils literal notranslate"><span class="pre">bucket_low</span></code> condition holds, see above), then |
| the sstable is added to the bucket.</dd> |
| </dl> |
| </div> |
| <div class="section" id="defragmentation"> |
| <h2>Defragmentation<a class="headerlink" href="#defragmentation" title="Permalink to this headline">¶</a></h2> |
| <p>Defragmentation is done when many sstables are touched during a read. The result of the read is put in to the memtable |
| so that the next read will not have to touch as many sstables. This can cause writes on a read-only-cluster.</p> |
| </div> |
| </div> |
| |
| |
| |
| |
| </div> |
| </div> |
| </div> |
| </div> |
| </div> |
