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<a href="/docs/latest/memory-configuration/eviction-policies"
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>Eviction Policies</a>
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<a href="/docs/latest/memory-configuration/replacement-policies"
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<a href="/docs/latest/persistence/native-persistence"
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<a href="/docs/latest/persistence/swap"
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<a href="/docs/latest/persistence/custom-cache-store"
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<a href="/docs/latest/persistence/snapshot-directory"
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<a href="/docs/latest/persistence/disk-compression"
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<a href="/docs/latest/persistence/persistence-tuning"
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<a href="/docs/latest/persistence/change-data-capture"
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<a href="/docs/latest/snapshots/snapshots" class='' >Cluster Snapshots</a>
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<a href="/docs/latest/configuring-caches/atomicity-modes"
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>Atomicity Modes</a>
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<a href="/docs/latest/configuring-caches/expiry-policies"
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<a href="/docs/latest/configuring-caches/cache-groups"
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<a href="/docs/latest/configuring-caches/near-cache"
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<li>
<a href="/docs/latest/data-rebalancing" class='' >Data Rebalancing</a>
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<a href="/docs/latest/data-streaming" class='' >Data Streaming</a>
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<button type='button' class='group-toggle collapsed '>Using Key-Value API<img class="state-indicator" src="/assets/images/left-nav-arrow.svg" width="6" height="10"></button>
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<a href="/docs/latest/key-value-api/using-cache-queries"
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<a href="/docs/latest/read-repair"
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<a href="/docs/latest/key-value-api/transactions" class='' >Performing Transactions</a>
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<a href="/docs/latest/machine-learning/updating-trained-models"
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<li><a href="/docs/latest/machine-learning/binary-classification/introduction" class=''>Introduction</a></li>
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<li><a href="/docs/latest/machine-learning/binary-classification/decision-trees" class=''>Decision Trees</a></li>
<li><a href="/docs/latest/machine-learning/binary-classification/multilayer-perceptron" class=''>Multilayer Perceptron</a></li>
<li><a href="/docs/latest/machine-learning/binary-classification/logistic-regression" class=''>Logistic Regression</a></li>
<li><a href="/docs/latest/machine-learning/binary-classification/knn-classification" class=''>k-NN Classification</a></li>
<li><a href="/docs/latest/machine-learning/binary-classification/ann" class=''>ANN (Approximate Nearest Neighbor)</a></li>
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<li><a href="/docs/latest/machine-learning/regression/decision-trees-regression" class=''>Decision Trees Regression</a></li>
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<li><a href="/docs/latest/machine-learning/clustering/gaussian-mixture" class=''>Gaussian mixture (GMM)</a></li>
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<li>
<a href="/docs/latest/machine-learning/preprocessing"
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<li><a href="/docs/latest/machine-learning/model-selection/introduction" class=''>Introduction</a></li>
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<li><a href="/docs/latest/machine-learning/model-selection/hyper-parameter-tuning" class=''>Hyper-parameter tuning</a></li>
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<li>
<a href="/docs/latest/machine-learning/multiclass-classification"
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<li><a href="/docs/latest/machine-learning/ensemble-methods/stacking" class=''>Stacking</a></li>
<li><a href="/docs/latest/machine-learning/ensemble-methods/baggin" class=''>Bagging</a></li>
<li><a href="/docs/latest/machine-learning/ensemble-methods/random-forest" class=''>Random Forest</a></li>
<li><a href="/docs/latest/machine-learning/ensemble-methods/gradient-boosting" class=''>Gradient Boosting</a></li>
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<li>
<a href="/docs/latest/machine-learning/recommendation-systems"
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<button
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<li><a href="/docs/latest/machine-learning/importing-model/introduction" class=''>Introduction</a></li>
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<li><a href="/docs/latest/machine-learning/importing-model/model-import-from-apache-spark" class=''>Import Model from Apache Spark</a></li>
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</li>
</nav>
</li>
<li>
<a href="/docs/latest/key-value-api/continuous-queries" class='' >Using Continuous Queries</a>
</li>
<li>
<a href="/docs/latest/services/services" class='' >Using Ignite Services</a>
</li>
<li>
<a href="/docs/latest/messaging" class='' >Using Ignite Messaging</a>
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<a href="/docs/latest/data-structures/queue-and-set"
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<a href="/docs/latest/data-structures/atomic-types"
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</li>
<li>
<a href="/docs/latest/data-structures/countdownlatch"
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</li>
<li>
<a href="/docs/latest/data-structures/atomic-sequence"
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</li>
<li>
<a href="/docs/latest/data-structures/semaphore"
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</li>
<li>
<a href="/docs/latest/data-structures/id-generator"
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</li>
<li>
<a href="/docs/latest/distributed-locks" class='' >Distributed Locks</a>
</li>
<li>
<a href="/docs/latest/restapi" class='' >REST API</a>
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<a class='edit-link' href="https://github.com/apache/ignite/tree/IGNITE-7595/docs/_docs/persistence/native-persistence-defragmentation.adoc" target="_blank">Edit</a>
<h1>Persistence Defragmentation</h1>
<div class="sect1">
<h2 id="overview">Overview</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Apache Ignite memory management mechanism can only create or reuse pages for user data, but it never frees them. So the files, where Ignite persists data, can only grow and never shrink.</p>
</div>
<div class="paragraph">
<p>In most use cases, it does not cause any problem as once created page can be reused multiple times. However, in certain cases, it is possible that cache contains very little data but occupies large chunks of disk space because a significant volume of data was removed from the cache.</p>
</div>
<div class="paragraph">
<p>Defragmentation enables a user to shrink data files and claim back disk space.</p>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<div class="paragraph">
<p>Defragmentation can only be used with historical rebalance enabled. If historical rebalancing is disabled, the server node always triggers full rebalance after the restart, which would throw away the defragmented partition. A full set of data is transferred to the node from other nodes over a network. Depending on the dataset’s size, transferring may require significant time and slow down the whole cluster as network capacity is essential to fulfill user requests.</p>
</div>
</td>
</tr>
</table>
</div>
</div>
</div>
<div class="sect1">
<h2 id="performing-defragmentation">Performing Defragmentation</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Defragmentation is a costly operation in terms of disk IO. To avoid slowing down user operations, note that defragmentation cannot be executed on a regular node joined to the cluster. To perform defragmentation, you need to request it first on a particular node or set of nodes and then restart them.</p>
</div>
<div class="sect2">
<h3 id="starting-defragmentation">Starting Defragmentation</h3>
<div class="paragraph">
<p>To request defragmentation, use the following command:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="shell">control.<span class="o">(</span>sh|bat<span class="o">)</span> <span class="nt">--defragmentation</span> schedule <span class="nt">--nodes</span> &lt;consistentIds&gt; <span class="o">[</span><span class="nt">--caches</span> &lt;cacheNames&gt;]</code></pre>
</div>
</div>
<div class="paragraph">
<p>After the manual restart, the node with the requested defragmentation enters a special mode called maintenance mode. The node in maintenance mode does not join the rest of the cluster but remains isolated until defragmentation is completed (or canceled by explicit user request). After that, the user has to restart the node one more time: it exits maintenance mode and returns to normal operations (joining the cluster and starting to serve regular workload).</p>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<div class="paragraph">
<p>Nodes in maintenance mode do not participate in serving the regular workload. It is not recommended to execute defragmentation on several nodes simultaneously as it reduces the number of backups, thus increasing the risk of partition loss.</p>
</div>
</td>
</tr>
</table>
</div>
</div>
<div class="sect2">
<h3 id="stopping-defragmentation">Stopping Defragmentation</h3>
<div class="paragraph">
<p>When a node executes defragmentation, it is possible to cancel it. To stop defragmentation, run the following command available in the control utility:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="shell">control.<span class="o">(</span>sh|bat<span class="o">)</span> <span class="nt">--defragmentation</span> cancel <span class="nt">--host</span> <span class="nt">--port</span></code></pre>
</div>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<div class="paragraph">
<p>To reduce disk space requirements during defragmentation, caches are defragmented one by one (if a defragmentation of more than one cache is requested). To calculate additional required space, find the cache that occupies the most disk space. The same amount of disk space is required for defragmentation at max.</p>
</div>
</td>
</tr>
</table>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="conclusion">Conclusion</h2>
<div class="sectionbody">
<div class="paragraph">
<p>In most situations, defragmentation is not necessary as existing memory management mechanism effectively reuses memory left after data deletion. But in rare cases, it may be necessary to employ it to free up disk space up.</p>
</div>
<div class="paragraph">
<p>Persistence defragmentation requires taking nodes out of their normal operations, so a careful planning is recommended.</p>
</div>
</div>
</div>
<div class="copyright">
© 2022 The Apache Software Foundation.<br/>
Apache, Apache Ignite, the Apache feather and the Apache Ignite logo are either registered trademarks or trademarks of The Apache Software Foundation.
</div>
</article>
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<ul class="sectlevel1">
<li><a href="#overview">Overview</a></li>
<li><a href="#performing-defragmentation">Performing Defragmentation</a>
<ul class="sectlevel2">
<li><a href="#starting-defragmentation">Starting Defragmentation</a></li>
<li><a href="#stopping-defragmentation">Stopping Defragmentation</a></li>
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