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<article data-swiftype-index='true'>
<a class='edit-link' href="https://github.com/apache/ignite/tree/IGNITE-7595/docs/_docs/memory-configuration/eviction-policies.adoc" target="_blank">Edit</a>
<h1>Eviction Policies</h1>
<div id="preamble">
<div class="sectionbody">
<div class="paragraph">
<p>When <a href="/docs/2.9.0/persistence/native-persistence">Native Persistence</a> is off, Ignite holds all cache entries in the off-heap memory and allocates pages as new data comes in.
When a memory limit is reached and Ignite cannot allocate a page, some of the data must be purged from memory to avoid OutOfMemory errors.
This process is called <em>eviction</em>. Eviction prevents the system from running out of memory but at the cost of losing data and having to reload it when you need it again.</p>
</div>
<div class="paragraph">
<p>Eviction is used in following cases:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>for off-heap memory when <a href="/docs/2.9.0/persistence/native-persistence">Native Persistence</a> is off;</p>
</li>
<li>
<p>for off-heap memory when Ignite is used with an <a href="/docs/2.9.0/persistence/external-storage">external storage</a>;</p>
</li>
<li>
<p>for <a href="/docs/2.9.0/configuring-caches/on-heap-caching">on-heap caches</a>;</p>
</li>
<li>
<p>for <a href="/docs/2.9.0/configuring-caches/near-cache">near caches</a> if configured.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>When Native Persistence is on, a similar process — called <em>page replacement</em> — is used to free up off-heap memory when Ignite cannot allocate a new page.
The difference is that the data is not lost (because it is stored in the persistent storage), and therefore you are less concerned about losing data than about efficiency.
Page replacement is automatically handled by Ignite and is not user-configurable.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="off-heap-memory-eviction">Off-Heap Memory Eviction</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Off-heap memory eviction is implemented as follows.</p>
</div>
<div class="paragraph">
<p>When memory usage exceeds the preset limit, Ignite applies one of the preconfigured algorithms to select a memory page that is most suitable for eviction.
Then, each cache entry contained in the page is removed from the page.
However, if an entry is locked by a transaction, it is retained.
Thus, either the entire page or a large chunk of it is emptied and is ready to be reused.</p>
</div>
<div class="imageblock">
<div class="content">
<img src="/docs/2.9.0/images/off_heap_memory_eviction.png" alt="Off-Heap Memory Eviction Mechanism">
</div>
</div>
<div class="paragraph">
<p>By default, off-heap memory eviction is disabled, which means that the used memory constantly grows until it reaches its limit.
To enable eviction, specify the page eviction mode in the <a href="/docs/2.9.0/memory-configuration/data-regions/">data region configuration</a>.
Note that off-heap memory eviction is configured per <a href="/docs/2.9.0/memory-configuration/data-regions">data region</a>.
If you don&#8217;t use data regions, you have to explicitly add default data region parameters in your configuration to be able to configure eviction.</p>
</div>
<div class="paragraph">
<p>By default, eviction starts when the overall RAM consumption by a region gets to 90%.
Use the <code>DataRegionConfiguration.setEvictionThreshold(&#8230;&#8203;)</code> parameter if you need to initiate eviction earlier or later.</p>
</div>
<div class="paragraph">
<p>Ignite supports two page selection algorithms:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Random-LRU</p>
</li>
<li>
<p>Random-2-LRU</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>The differences between the two are explained below.</p>
</div>
<div class="sect2">
<h3 id="random-lru">Random-LRU</h3>
<div class="paragraph">
<p>To enable the Random-LRU eviction algorithm, configure the data region as shown below:</p>
</div>
<code-tabs><code-tab data-tab='XML'><div class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="xml"><span class="nt">&lt;bean</span> <span class="na">class=</span><span class="s">"org.apache.ignite.configuration.IgniteConfiguration"</span><span class="nt">&gt;</span>
<span class="c">&lt;!-- Memory configuration. --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"dataStorageConfiguration"</span><span class="nt">&gt;</span>
<span class="nt">&lt;bean</span> <span class="na">class=</span><span class="s">"org.apache.ignite.configuration.DataStorageConfiguration"</span><span class="nt">&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"dataRegionConfigurations"</span><span class="nt">&gt;</span>
<span class="nt">&lt;list&gt;</span>
<span class="c">&lt;!-- Defining a data region that will consume up to 20 GB of RAM. --&gt;</span>
<span class="nt">&lt;bean</span> <span class="na">class=</span><span class="s">"org.apache.ignite.configuration.DataRegionConfiguration"</span><span class="nt">&gt;</span>
<span class="c">&lt;!-- Custom region name. --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"name"</span> <span class="na">value=</span><span class="s">"20GB_Region"</span><span class="nt">/&gt;</span>
<span class="c">&lt;!-- 500 MB initial size (RAM). --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"initialSize"</span> <span class="na">value=</span><span class="s">"#{500L * 1024 * 1024}"</span><span class="nt">/&gt;</span>
<span class="c">&lt;!-- 20 GB maximum size (RAM). --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"maxSize"</span> <span class="na">value=</span><span class="s">"#{20L * 1024 * 1024 * 1024}"</span><span class="nt">/&gt;</span>
<span class="c">&lt;!-- Enabling RANDOM_LRU eviction for this region. --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"pageEvictionMode"</span> <span class="na">value=</span><span class="s">"RANDOM_LRU"</span><span class="nt">/&gt;</span>
<span class="nt">&lt;/bean&gt;</span>
<span class="nt">&lt;/list&gt;</span>
<span class="nt">&lt;/property&gt;</span>
<span class="nt">&lt;/bean&gt;</span>
<span class="nt">&lt;/property&gt;</span>
<span class="nt">&lt;/bean&gt;</span>
<span class="nt">&lt;bean</span> <span class="na">class=</span><span class="s">"org.apache.ignite.configuration.IgniteConfiguration"</span><span class="nt">&gt;</span>
<span class="c">&lt;!-- Memory configuration. --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"dataStorageConfiguration"</span><span class="nt">&gt;</span>
<span class="nt">&lt;bean</span> <span class="na">class=</span><span class="s">"org.apache.ignite.configuration.DataStorageConfiguration"</span><span class="nt">&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"dataRegionConfigurations"</span><span class="nt">&gt;</span>
<span class="nt">&lt;list&gt;</span>
<span class="c">&lt;!--
Defining a data region that consumes up to 20 GB of RAM.
--&gt;</span>
<span class="nt">&lt;bean</span> <span class="na">class=</span><span class="s">"org.apache.ignite.configuration.DataRegionConfiguration"</span><span class="nt">&gt;</span>
<span class="c">&lt;!-- Custom region name. --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"name"</span> <span class="na">value=</span><span class="s">"20GB_Region"</span><span class="nt">/&gt;</span>
<span class="c">&lt;!-- 500 MB initial size (RAM). --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"initialSize"</span> <span class="na">value=</span><span class="s">"#{500L * 1024 * 1024}"</span><span class="nt">/&gt;</span>
<span class="c">&lt;!-- 20 GB maximum size (RAM). --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"maxSize"</span> <span class="na">value=</span><span class="s">"#{20L * 1024 * 1024 * 1024}"</span><span class="nt">/&gt;</span>
<span class="c">&lt;!-- Enabling RANDOM_LRU eviction for this region. --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"pageEvictionMode"</span> <span class="na">value=</span><span class="s">"RANDOM_LRU"</span><span class="nt">/&gt;</span>
<span class="nt">&lt;/bean&gt;</span>
<span class="nt">&lt;/list&gt;</span>
<span class="nt">&lt;/property&gt;</span>
<span class="nt">&lt;/bean&gt;</span>
<span class="nt">&lt;/property&gt;</span>
<span class="c">&lt;!-- The rest of the configuration. --&gt;</span>
<span class="nt">&lt;/bean&gt;</span></code></pre>
</div>
</div></code-tab><code-tab data-tab='Java'><div class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="java"><span class="c1">// Node configuration.</span>
<span class="nc">IgniteConfiguration</span> <span class="n">cfg</span> <span class="o">=</span> <span class="k">new</span> <span class="nc">IgniteConfiguration</span><span class="o">();</span>
<span class="c1">// Memory configuration.</span>
<span class="nc">DataStorageConfiguration</span> <span class="n">storageCfg</span> <span class="o">=</span> <span class="k">new</span> <span class="nc">DataStorageConfiguration</span><span class="o">();</span>
<span class="c1">// Creating a new data region.</span>
<span class="nc">DataRegionConfiguration</span> <span class="n">regionCfg</span> <span class="o">=</span> <span class="k">new</span> <span class="nc">DataRegionConfiguration</span><span class="o">();</span>
<span class="c1">// Region name.</span>
<span class="n">regionCfg</span><span class="o">.</span><span class="na">setName</span><span class="o">(</span><span class="s">"20GB_Region"</span><span class="o">);</span>
<span class="c1">// 500 MB initial size (RAM).</span>
<span class="n">regionCfg</span><span class="o">.</span><span class="na">setInitialSize</span><span class="o">(</span><span class="mi">500L</span> <span class="o">*</span> <span class="mi">1024</span> <span class="o">*</span> <span class="mi">1024</span><span class="o">);</span>
<span class="c1">// 20 GB max size (RAM).</span>
<span class="n">regionCfg</span><span class="o">.</span><span class="na">setMaxSize</span><span class="o">(</span><span class="mi">20L</span> <span class="o">*</span> <span class="mi">1024</span> <span class="o">*</span> <span class="mi">1024</span> <span class="o">*</span> <span class="mi">1024</span><span class="o">);</span>
<span class="c1">// Enabling RANDOM_LRU eviction for this region.</span>
<span class="n">regionCfg</span><span class="o">.</span><span class="na">setPageEvictionMode</span><span class="o">(</span><span class="nc">DataPageEvictionMode</span><span class="o">.</span><span class="na">RANDOM_LRU</span><span class="o">);</span>
<span class="c1">// Setting the data region configuration.</span>
<span class="n">storageCfg</span><span class="o">.</span><span class="na">setDataRegionConfigurations</span><span class="o">(</span><span class="n">regionCfg</span><span class="o">);</span>
<span class="c1">// Applying the new configuration.</span>
<span class="n">cfg</span><span class="o">.</span><span class="na">setDataStorageConfiguration</span><span class="o">(</span><span class="n">storageCfg</span><span class="o">);</span></code></pre>
</div>
</div></code-tab><code-tab data-tab='C#/.NET'><div class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="csharp"><span class="kt">var</span> <span class="n">cfg</span> <span class="p">=</span> <span class="k">new</span> <span class="n">IgniteConfiguration</span>
<span class="p">{</span>
<span class="n">DataStorageConfiguration</span> <span class="p">=</span> <span class="k">new</span> <span class="n">DataStorageConfiguration</span>
<span class="p">{</span>
<span class="n">DataRegionConfigurations</span> <span class="p">=</span> <span class="k">new</span><span class="p">[]</span>
<span class="p">{</span>
<span class="k">new</span> <span class="n">DataRegionConfiguration</span>
<span class="p">{</span>
<span class="n">Name</span> <span class="p">=</span> <span class="s">"20GB_Region"</span><span class="p">,</span>
<span class="n">InitialSize</span> <span class="p">=</span> <span class="m">500L</span> <span class="p">*</span> <span class="m">1024</span> <span class="p">*</span> <span class="m">1024</span><span class="p">,</span>
<span class="n">MaxSize</span> <span class="p">=</span> <span class="m">20L</span> <span class="p">*</span> <span class="m">1024</span> <span class="p">*</span> <span class="m">1024</span> <span class="p">*</span> <span class="m">1024</span><span class="p">,</span>
<span class="n">PageEvictionMode</span> <span class="p">=</span> <span class="n">DataPageEvictionMode</span><span class="p">.</span><span class="n">RandomLru</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">};</span></code></pre>
</div>
</div></code-tab><code-tab data-tab='C++' data-unavailable='true'><div class="listingblock">
<div class="content">
<pre class="rouge highlight"><code>This API is not presently available for C++. You can use XML configuration.</code></pre>
</div>
</div></code-tab></code-tabs>
<div class="paragraph">
<p>Random-LRU algorithm works as follows:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Once a memory region defined by a memory policy is configured, an off-heap array is allocated to track the 'last usage' timestamp for every individual data page.</p>
</li>
<li>
<p>When a data page is accessed, its timestamp gets updated in the tracking array.</p>
</li>
<li>
<p>When it is time to evict a page, the algorithm randomly chooses 5 indexes from the tracking array and evicts the page with the oldest timestamp. If some of the indexes point to non-data pages (index or system pages), then the algorithm picks another page.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="random-2-lru">Random-2-LRU</h3>
<div class="paragraph">
<p>To enable Random-2-LRU eviction algorithm, which is a scan-resistant version of Random-LRU, configure the data region, as shown in the example below:</p>
</div>
<code-tabs><code-tab data-tab='XML'><div class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="xml"><span class="nt">&lt;bean</span> <span class="na">class=</span><span class="s">"org.apache.ignite.configuration.IgniteConfiguration"</span><span class="nt">&gt;</span>
<span class="c">&lt;!-- Memory configuration. --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"dataStorageConfiguration"</span><span class="nt">&gt;</span>
<span class="nt">&lt;bean</span> <span class="na">class=</span><span class="s">"org.apache.ignite.configuration.DataStorageConfiguration"</span><span class="nt">&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"dataRegionConfigurations"</span><span class="nt">&gt;</span>
<span class="nt">&lt;list&gt;</span>
<span class="c">&lt;!--
Defining a data region that consumes up to 20 GB of RAM.
--&gt;</span>
<span class="nt">&lt;bean</span> <span class="na">class=</span><span class="s">"org.apache.ignite.configuration.DataRegionConfiguration"</span><span class="nt">&gt;</span>
<span class="c">&lt;!-- Custom region name. --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"name"</span> <span class="na">value=</span><span class="s">"20GB_Region"</span><span class="nt">/&gt;</span>
<span class="c">&lt;!-- 500 MB initial size (RAM). --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"initialSize"</span> <span class="na">value=</span><span class="s">"#{500L * 1024 * 1024}"</span><span class="nt">/&gt;</span>
<span class="c">&lt;!-- 20 GB maximum size (RAM). --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"maxSize"</span> <span class="na">value=</span><span class="s">"#{20L * 1024 * 1024 * 1024}"</span><span class="nt">/&gt;</span>
<span class="c">&lt;!-- Enabling RANDOM_2_LRU eviction for this region. --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"pageEvictionMode"</span> <span class="na">value=</span><span class="s">"RANDOM_2_LRU"</span><span class="nt">/&gt;</span>
<span class="nt">&lt;/bean&gt;</span>
<span class="nt">&lt;/list&gt;</span>
<span class="nt">&lt;/property&gt;</span>
<span class="nt">&lt;/bean&gt;</span>
<span class="nt">&lt;/property&gt;</span>
<span class="c">&lt;!-- The rest of the configuration. --&gt;</span>
<span class="nt">&lt;/bean&gt;</span></code></pre>
</div>
</div></code-tab><code-tab data-tab='Java'><div class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="java"><span class="c1">// Ignite configuration.</span>
<span class="nc">IgniteConfiguration</span> <span class="n">cfg</span> <span class="o">=</span> <