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<a href="/docs/latest/snapshots/snapshots" class='' >Cluster Snapshots</a>
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<a href="/docs/latest/data-rebalancing" class='' >Data Rebalancing</a>
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<li><a href="/docs/latest/machine-learning/binary-classification/ann" class=''>ANN (Approximate Nearest Neighbor)</a></li>
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<a href="/docs/latest/machine-learning/preprocessing"
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<a href="/docs/latest/machine-learning/multiclass-classification"
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<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>
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<a href="/docs/latest/machine-learning/recommendation-systems"
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<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>
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<a href="/docs/latest/messaging" class='' >Using Ignite Messaging</a>
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<a href="/docs/latest/data-structures/atomic-types"
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<a href="/docs/latest/data-structures/countdownlatch"
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<a href="/docs/latest/data-structures/atomic-sequence"
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<a href="/docs/latest/data-structures/semaphore"
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<article data-swiftype-index='true'>
<a class='edit-link' href="https://github.com/apache/ignite/tree/IGNITE-7595/docs/_docs/persistence/native-persistence.adoc" target="_blank">Edit</a>
<h1>Ignite Persistence</h1>
<div class="sect1">
<h2 id="overview">Overview</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Ignite Persistence, or Native Persistence, is a set of features designed to provide persistent storage.
When it is enabled, Ignite always stores all the data on disk, and loads as much data as it can into RAM for processing.
For example, if there are 100 entries and RAM has the capacity to store only 20, then all 100 are stored on disk and only 20 are cached in RAM for better performance.</p>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
For more information on Native Persistence, watch <a href="https://www.youtube.com/watch?v=6Yg5QW-XFVc&amp;list=PLMc7NR20hA-KF8c_hVICKpzKnWkjzfC2V&amp;index=19" target="_blank" rel="noopener">the architectural deep dive</a> on the internals of the Ignite storage engine.
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>When Native persistence is turned off and no external storage is used, Ignite behaves as a pure in-memory store.</p>
</div>
<div class="paragraph">
<p>When persistence is enabled, every server node persists a subset of the data that only includes the partitions that are assigned to that node (including <a href="/docs/latest/data-modeling/data-partitioning#backup-partitions">backup partitions</a> if backups are enabled).</p>
</div>
<div class="paragraph">
<p>The Native Persistence functionality is based on the following features:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Storing data partitions on disk</p>
</li>
<li>
<p>Write-ahead logging</p>
</li>
<li>
<p>Checkpointing</p>
</li>
<li>
<p>Usage of OS swap</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>When persistence is enabled, Ignite stores each partition in a separate file on disk.
The data format of the partition files is the same as that of the data when it is kept in memory.
If partition backups are enabled, they are also saved on disk.
In addition to data partitions, Ignite stores indexes and metadata.</p>
</div>
<div class="imageblock">
<div class="content">
<img src="/docs/2.11.0/images/persistent_store_structure.png" alt="persistent store structure">
</div>
</div>
<div class="paragraph">
<p>You can change the default location of data files in the <a href="#configuration-properties">configuration</a>.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="enabling-persistent-storage">Enabling Persistent Storage</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Native Persistence is configured per <a href="/docs/latest/memory-configuration/data-regions">data region</a>.
To enable persistent storage, set the <code>persistenceEnabled</code> property to <code>true</code> in the data region configuration.
You can have in-memory data regions and data regions with persistence at the same time.</p>
</div>
<div class="paragraph">
<p>The following example shows how to enable persistent storage for the default data region.</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="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">"defaultDataRegionConfiguration"</span><span class="nt">&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="nt">&lt;property</span> <span class="na">name=</span><span class="s">"persistenceEnabled"</span> <span class="na">value=</span><span class="s">"true"</span><span class="nt">/&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;/property&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="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">//data storage 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="n">storageCfg</span><span class="o">.</span><span class="na">getDefaultDataRegionConfiguration</span><span class="o">().</span><span class="na">setPersistenceEnabled</span><span class="o">(</span><span class="kc">true</span><span class="o">);</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>
<span class="nc">Ignite</span> <span class="n">ignite</span> <span class="o">=</span> <span class="nc">Ignition</span><span class="o">.</span><span class="na">start</span><span class="o">(</span><span class="n">cfg</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">DefaultDataRegionConfiguration</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">"Default_Region"</span><span class="p">,</span>
<span class="n">PersistenceEnabled</span> <span class="p">=</span> <span class="k">true</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">};</span>
<span class="n">Ignition</span><span class="p">.</span><span class="nf">Start</span><span class="p">(</span><span class="n">cfg</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>
</div>
<div class="sect1">
<h2 id="configuring-persistent-storage-directory">Configuring Persistent Storage Directory</h2>
<div class="sectionbody">
<div class="paragraph">
<p>When persistence is enabled, the node stores user data, indexes and WAL files in the <code>{IGNITE_WORK_DIR}/db</code> directory.
This directory is referred to as the storage directory.
You can change the storage directory by setting the <code>storagePath</code> property of the <code>DataStorageConfiguration</code> object, as shown below.</p>
</div>
<div class="paragraph">
<p>Each node maintains the following sub-directories under the storage directory meant to store cache data, WAL files, and WAL archive files:</p>
</div>
<table class="tableblock frame-all grid-all stripes-even stretch">
<colgroup>
<col style="width: 42.8571%;">
<col style="width: 57.1429%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Subdirectory name</th>
<th class="tableblock halign-left valign-top">Description</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">{WORK_DIR}/db/{nodeId}</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">This directory contains cache data and indexes.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">{WORK_DIR}/db/wal/{nodeId}</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">This directory contains WAL files.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">{WORK_DIR}/db/wal/archive/{nodeId}</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">This directory contains WAL archive files.</p></td>
</tr>
</tbody>
</table>
<div class="paragraph">
<p><code>nodeId</code> here is either the consistent node ID (if it&#8217;s defined in the node configuration) or <a href="https://cwiki.apache.org/confluence/display/IGNITE/Ignite+Persistent+Store+-+under+the+hood#IgnitePersistentStore-underthehood-SubfoldersGeneration" target="_blank" rel="noopener">auto-generated node id</a>. It is used to ensure uniqueness of the directories for the node.
If multiple nodes share the same work directory, they uses different sub-directories.</p>
</div>
<div class="paragraph">
<p>If the work directory contains persistence files for multiple nodes (there are multiple {nodeId} subdirectories with different nodeIds), the node picks up the first subdirectory that is not being used.
To make sure a node always uses a specific subdirectory and, thus, specific data partitions even after restarts, set <code>IgniteConfiguration.setConsistentId</code> to a cluster-wide unique value in the node configuration.</p>
</div>
<div class="paragraph">
<p>You can change the storage directory as follows:</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="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">"defaultDataRegionConfiguration"</span><span class="nt">&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="nt">&lt;property</span> <span class="na">name=</span><span class="s">"persistenceEnabled"</span> <span class="na">value=</span><span class="s">"true"</span><span class="nt">/&gt;</span>
<span class="nt">&lt;/bean&gt;</span>
<span class="nt">&lt;/property&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"storagePath"</span> <span class="na">value=</span><span class="s">"/opt/storage"</span><span class="nt">/&gt;</span>
<span class="nt">&lt;/bean&gt;</span>
<span class="nt">&lt;/property&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="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">//data storage 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="n">storageCfg</span><span class="o">.</span><span class="na">getDefaultDataRegionConfiguration</span><span class="o">().</span><span class="na">setPersistenceEnabled</span><span class="o">(</span><span class="kc">true</span><span class="o">);</span>
<span class="n">storageCfg</span><span class="o">.</span><span class="na">setStoragePath</span><span class="o">(</span><span class="s">"/opt/storage"</span><span class="o">);</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>
<span class="nc">Ignite</span> <span class="n">ignite</span> <span class="o">=</span> <span class="nc">Ignition</span><span class="o">.</span><span class="na">start</span><span class="o">(</span><span class="n">cfg</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">StoragePath</span> <span class="p">=</span> <span class="s">"/ssd/storage"</span><span class="p">,</span>
<span class="n">DefaultDataRegionConfiguration</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">"Default_Region"</span><span class="p">,</span>
<span class="n">PersistenceEnabled</span> <span class="p">=</span> <span class="k">true</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">};</span>
<span class="n">Ignition</span><span class="p">.</span><span class="nf">Start</span><span class="p">(</span><span class="n">cfg</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>You can also change the WAL and WAL archive paths to point to directories outside of the storage directory. Refer to the next section for details.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="write-ahead-log">Write-Ahead Log</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The write-ahead log is a log of all data modifying operations (including deletes) that happen on a node. When a page is updated in RAM, the update is not directly written to the partition file but is appended to the tail of the WAL.</p>
</div>
<div class="paragraph">
<p>The purpose of the write-ahead log is to provide a recovery mechanism for scenarios where a single node or the whole cluster goes down. In case of a crash or restart, the cluster can always be recovered to the latest successfully committed transaction by relying on the content of the WAL.</p>
</div>
<div class="paragraph">
<p>The WAL consists of several files (called active segments) and an archive. The active segments are filled out sequentially and are overwritten in a cyclical order. Once the 1st segment is full, its content is copied to the WAL archive (see the <a href="#wal-archive">WAL Archive</a> section below). While the 1st segment is being copied, the 2nd segment is treated as an active WAL file and accepts all the updates coming from the application side. By default, there are 10 active segments.</p>
</div>
<div class="sect2">
<h3 id="wal-modes">WAL Modes</h3>
<div class="paragraph">
<p>There are three WAL modes. Each mode differs in how it affects performance and provides different consistency guarantees.</p>
</div>
<table class="tableblock frame-all grid-all stripes-even stretch">
<colgroup>
<col style="width: 20%;">
<col style="width: 45%;">
<col style="width: 35%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Mode</th>
<th class="tableblock halign-left valign-top">Description</th>
<th class="tableblock halign-left valign-top">Consistency Guarantees</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>FSYNC</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">The changes are guaranteed to be persisted to disk for every atomic write or transactional commit.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Data updates are never lost surviving any OS or process crashes, or power failure.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>LOG_ONLY</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">The default mode.</p>
<p class="tableblock">The changes are guaranteed to be flushed to either the OS buffer cache or a memory-mapped file for every atomic write or transactional commit.</p>
<p class="tableblock">The memory-mapped file approach is used by default and can be switched off by setting the <code>IGNITE_WAL_MMAP</code> system property to <code>false</code>.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Data updates survive a process crash.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>BACKGROUND</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">When the <code>IGNITE_WAL_MMAP</code> property is enabled (default), this mode behaves like the <code>LOG_ONLY</code> mode.</p>
<p class="tableblock">If the memory-mapped file approach is disabled then the changes stay in node&#8217;s internal buffer and are periodically flushed to disk. The frequency of flushing is specified via the <code>walFlushFrequency</code> parameter.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">When the <code>IGNITE_WAL_MMAP</code> property is enabled (default), the mode provides the same guarantees as <code>LOG_ONLY</code> mode.</p>
<p class="tableblock">Otherwise, recent data updates may get lost in case of a process crash or other outages.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>NONE</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">WAL is disabled. The changes are persisted only if you shut down the node gracefully.
Use <code>Ignite.active(false)</code> to deactivate the cluster and shut down the node.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Data loss might occur.</p>
<p class="tableblock">If a node is terminated abruptly during update operations, it is very likely that the data stored on the disk becomes out-of-sync or corrupted.</p></td>
</tr>
</tbody>
</table>
</div>
<div class="sect2">
<h3 id="wal-archive">WAL Archive</h3>
<div class="paragraph">
<p>The WAL archive is used to store WAL segments that may be needed to recover the node after a crash. The number of segments kept in the archive is such that the total size of all segments does not exceed the specified size of the WAL archive.</p>
</div>
<div class="paragraph">
<p>By default, the maximum size of the WAL archive (total space it occupies on disk) is defined as 4 times the size of the <a href="/docs/latest/persistence/persistence-tuning#adjusting-checkpointing-buffer-size">checkpointing buffer</a>. You can change that value in the <a href="#configuration-properties">configuration</a>.</p>
</div>
<div class="admonitionblock caution">
<table>
<tr>
<td class="icon">
<div class="title">Caution</div>
</td>
<td class="content">
Setting the WAL archive size to a value lower than the default may impact performance and should be tested before being used in production.
</td>
</tr>
</table>
</div>
</div>
<div class="sect2">
<h3 id="changing-wal-segment-size">Changing WAL Segment Size</h3>
<div class="paragraph">
<p>The default WAL segment size (64 MB) may be inefficient in high load scenarios because it causes WAL to switch between segments too frequently and switching/rotation is a costly operation.
A larger size of WAL segments can help increase performance under high loads at the cost of increasing the total size of the WAL files and WAL archive.</p>
</div>
<div class="paragraph">
<p>You can change the size of the WAL segment files in the data storage configuration. The value must be between 512KB and 2GB.</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="na">id=</span><span class="s">"ignite.cfg"</span><span class="nt">&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="c">&lt;!-- set the size of wal segments to 128MB --&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"walSegmentSize"</span> <span class="na">value=</span><span class="s">"#{128 * 1024 * 1024}"</span><span class="nt">/&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"defaultDataRegionConfiguration"</span><span class="nt">&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="nt">&lt;property</span> <span class="na">name=</span><span class="s">"persistenceEnabled"</span> <span class="na">value=</span><span class="s">"true"</span><span class="nt">/&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;/property&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="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="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="n">storageCfg</span><span class="o">.</span><span class="na">getDefaultDataRegionConfiguration</span><span class="o">().</span><span class="na">setPersistenceEnabled</span><span class="o">(</span><span class="kc">true</span><span class="o">);</span>
<span class="n">storageCfg</span><span class="o">.</span><span class="na">setWalSegmentSize</span><span class="o">(</span><span class="mi">128</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="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>
<span class="nc">Ignite</span> <span class="n">ignite</span> <span class="o">=</span> <span class="nc">Ignition</span><span class="o">.</span><span class="na">start</span><span class="o">(</span><span class="n">cfg</span><span class="o">);</span></code></pre>
</div>
</div></code-tab><code-tab data-tab='C#/.NET' data-unavailable='true'><div class="listingblock">
<div class="content">
<pre class="rouge highlight"><code>This API is not presently available for C#/.NET. You can use XML configuration.</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>
<div class="sect2">
<h3 id="disabling-wal">Disabling WAL</h3>
<div class="admonitionblock warning">
<table>
<tr>
<td class="icon">
<div class="title">Warning</div>
</td>
<td class="content">
Disabling or enabling WAL should only be done on stable topology: all baseline nodes should be present, no nodes should join or leave the cluster for the duration of this operation. Otherwise, cache may be stuck in inconsistent state. If that happens, it is advised to destroy the affected cache(s).
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>There are situations when it is reasonable to have the WAL disabled to get better performance. For instance, it is useful to disable WAL during initial data loading and enable it after the pre-loading is complete.</p>
</div>
<code-tabs><code-tab data-tab='Java'><div class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="java"><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="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="n">storageCfg</span><span class="o">.</span><span class="na">getDefaultDataRegionConfiguration</span><span class="o">().</span><span class="na">setPersistenceEnabled</span><span class="o">(</span><span class="kc">true</span><span class="o">);</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>
<span class="nc">Ignite</span> <span class="n">ignite</span> <span class="o">=</span> <span class="nc">Ignition</span><span class="o">.</span><span class="na">start</span><span class="o">(</span><span class="n">cfg</span><span class="o">);</span>
<span class="n">ignite</span><span class="o">.</span><span class="na">cluster</span><span class="o">().</span><span class="na">state</span><span class="o">(</span><span class="nc">ClusterState</span><span class="o">.</span><span class="na">ACTIVE</span><span class="o">);</span>
<span class="nc">String</span> <span class="n">cacheName</span> <span class="o">=</span> <span class="s">"myCache"</span><span class="o">;</span>
<span class="n">ignite</span><span class="o">.</span><span class="na">getOrCreateCache</span><span class="o">(</span><span class="n">cacheName</span><span class="o">);</span>
<span class="n">ignite</span><span class="o">.</span><span class="na">cluster</span><span class="o">().</span><span class="na">disableWal</span><span class="o">(</span><span class="n">cacheName</span><span class="o">);</span>
<span class="c1">//load data</span>
<span class="n">ignite</span><span class="o">.</span><span class="na">cluster</span><span class="o">().</span><span class="na">enableWal</span><span class="o">(</span><span class="n">cacheName</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">cacheName</span> <span class="p">=</span> <span class="s">"myCache"</span><span class="p">;</span>
<span class="kt">var</span> <span class="n">ignite</span> <span class="p">=</span> <span class="n">Ignition</span><span class="p">.</span><span class="nf">Start</span><span class="p">();</span>
<span class="n">ignite</span><span class="p">.</span><span class="nf">GetCluster</span><span class="p">().</span><span class="nf">DisableWal</span><span class="p">(</span><span class="n">cacheName</span><span class="p">);</span>
<span class="c1">//load data</span>
<span class="n">ignite</span><span class="p">.</span><span class="nf">GetCluster</span><span class="p">().</span><span class="nf">EnableWal</span><span class="p">(</span><span class="n">cacheName</span><span class="p">);</span></code></pre>
</div>
</div></code-tab><code-tab data-tab='SQL'><div class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="sql"><span class="k">ALTER</span> <span class="k">TABLE</span> <span class="n">Person</span> <span class="n">NOLOGGING</span>
<span class="o">//</span><span class="p">...</span>
<span class="k">ALTER</span> <span class="k">TABLE</span> <span class="n">Person</span> <span class="n">LOGGING</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++.</code></pre>
</div>
</div></code-tab></code-tabs>
<div class="admonitionblock warning">
<table>
<tr>
<td class="icon">
<div class="title">Warning</div>
</td>
<td class="content">
If WAL is disabled and you restart a node, all data is removed from the persistent storage on that node. This is implemented because without WAL data consistency cannot be guaranteed in case of node crash or restart.
</td>
</tr>
</table>
</div>
</div>
<div class="sect2">
<h3 id="wal-archive-compaction">WAL Archive Compaction</h3>
<div class="paragraph">
<p>You can enable WAL Archive compaction to reduce the space occupied by the WAL Archive.
By default, WAL Archive contains segments for the last 20 checkpoints (this number is configurable).
If compaction is enabled, all archived segments that are 1 checkpoint old are compressed in ZIP format.
If the segments are needed (for example, to re-balance data between nodes), they are uncompressed to RAW format.</p>
</div>
<div class="paragraph">
<p>See the <a href="#configuration-properties">Configuration Properties</a> section below to learn how to enable WAL archive compaction.</p>
</div>
</div>
<div class="sect2">
<h3 id="wal-records-compression">WAL Records Compression</h3>
<div class="paragraph">
<p>As described in the <a href="https://cwiki.apache.org/confluence/display/IGNITE/Ignite+Persistent+Store+-+under+the+hood#IgnitePersistentStore-underthehood-WAL">design document</a>, physical and logical records that represent data updates are written to the WAL files before the user operation is acknowledged.
Ignite can compress WAL records in memory before they are written to disk to save space.</p>
</div>
<div class="paragraph">
<p>WAL Records Compression requires that the 'ignite-compress' module be enabled. See <a href="/docs/latest/setup#enabling-modules">Enabling Modules</a>.</p>
</div>
<div class="paragraph">
<p>By default WAL records compression is disabled.
To enable it, set the compression algorithm and compression level in the data storage configuration:</p>
</div>
<code-tabs><code-tab data-tab='XML'></code-tab><code-tab data-tab='Java'><div class="listingblock">
<div class="content">
<pre class="rouge highlight"><code data-lang="java"><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="nc">DataStorageConfiguration</span> <span class="n">dsCfg</span> <span class="o">=</span> <span class="k">new</span> <span class="nc">DataStorageConfiguration</span><span class="o">();</span>
<span class="n">dsCfg</span><span class="o">.</span><span class="na">getDefaultDataRegionConfiguration</span><span class="o">().</span><span class="na">setPersistenceEnabled</span><span class="o">(</span><span class="kc">true</span><span class="o">);</span>
<span class="c1">//WAL page compression parameters</span>
<span class="n">dsCfg</span><span class="o">.</span><span class="na">setWalPageCompression</span><span class="o">(</span><span class="nc">DiskPageCompression</span><span class="o">.</span><span class="na">LZ4</span><span class="o">);</span>
<span class="n">dsCfg</span><span class="o">.</span><span class="na">setWalPageCompressionLevel</span><span class="o">(</span><span class="mi">8</span><span class="o">);</span>
<span class="n">cfg</span><span class="o">.</span><span class="na">setDataStorageConfiguration</span><span class="o">(</span><span class="n">dsCfg</span><span class="o">);</span>
<span class="nc">Ignite</span> <span class="n">ignite</span> <span class="o">=</span> <span class="nc">Ignition</span><span class="o">.</span><span class="na">start</span><span class="o">(</span><span class="n">cfg</span><span class="o">);</span></code></pre>
</div>
</div></code-tab><code-tab data-tab='C#/.NET'></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>The supported compression algorithms are listed in <a href="https://ignite.apache.org/releases/2.11.0/javadoc/org/apache/ignite/configuration/DiskPageCompression.html" target="_blank" rel="noopener">DiskPageCompression</a>.</p>
</div>
</div>
<div class="sect2">
<h3 id="disabling-wal-archive">Disabling WAL Archive</h3>
<div class="paragraph">
<p>In some cases, you may want to disable WAL archiving, for example, to reduce the overhead associated with copying of WAL segments to the archive. There can be a situation where Ignite writes data to WAL segments faster than the segments are copied to the archive. This may create an I/O bottleneck that can freeze the operation of the node. If you experience such problems, try disabling WAL archiving.</p>
</div>
<div class="paragraph">
<p>To disable archiving, set the WAL path and the WAL archive path to the same value.
In this case, Ignite does not copy segments to the archive; instead, it creates new segments in the WAL folder.
Old segments are deleted as the WAL grows, based on the WAL Archive size setting.</p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="checkpointing">Checkpointing</h2>
<div class="sectionbody">
<div class="paragraph">
<p><em>Checkpointing</em> is the process of copying dirty pages from RAM to partition files on disk. A dirty page is a page that was updated in RAM but was not written to the respective partition file (the update, however, was appended to the WAL).</p>
</div>
<div class="paragraph">
<p>After a checkpoint is created, all changes are persisted to disk and will be available if the node crashes and is restarted.</p>
</div>
<div class="paragraph">
<p>Checkpointing and write-ahead logging are designed to ensure durability of data and recovery in case of a node failure.</p>
</div>
<div class="paragraph">
<p><span class="image"><img src="/docs/2.11.0/images/checkpointing-persistence.png" alt="checkpointing persistence"></span></p>
</div>
<div class="paragraph">
<p>This process helps to utilize disk space frugally by keeping pages in the most up-to-date state on disk. After a checkpoint is passed, you can delete the WAL segments that were created before that point in time.</p>
</div>
<div class="paragraph">
<p>See the following related documentation:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><a href="/docs/latest/monitoring-metrics/metrics#monitoring-checkpointing-operations">Monitoring Checkpointing Operations</a>.</p>
</li>
<li>
<p><a href="/docs/latest/persistence/persistence-tuning#adjusting-checkpointing-buffer-size">Adjusting Checkpointing Buffer Size</a></p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="configuration-properties">Configuration Properties</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The following table describes some properties of <a href="https://ignite.apache.org/releases/2.11.0/javadoc/org/apache/ignite/configuration/DataStorageConfiguration.html">DataStorageConfiguration</a>.</p>
</div>
<table class="tableblock frame-all grid-all stripes-even stretch">
<colgroup>
<col style="width: 25%;">
<col style="width: 50%;">
<col style="width: 25%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Property Name</th>
<th class="tableblock halign-left valign-top">Description</th>
<th class="tableblock halign-left valign-top">Default Value</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>persistenceEnabled</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Set this property to <code>true</code> to enable Native Persistence.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>false</code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>storagePath</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">The path where data is stored.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>${IGNITE_HOME}/work/db/node{IDX}-{UUID}</code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>walPath</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">The path to the directory where active WAL segments are stored.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>${IGNITE_HOME}/work/db/wal/</code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>walArchivePath</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">The path to the WAL archive.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>${IGNITE_HOME}/work/db/wal/archive/</code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>walCompactionEnabled</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Set to <code>true</code> to enable <a href="#wal-archive-compaction">WAL archive compaction</a>.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>false</code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>walSegmentSize</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">The size of a WAL segment file in bytes.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">64MB</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>walMode</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="#wal-modes">Write-ahead logging mode</a>.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>LOG_ONLY</code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>walCompactionLevel</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">WAL archive compression level. <code>1</code> indicates the fastest speed, and <code>9</code> indicates the best compression.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>1</code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>maxWalArchiveSize</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">The maximum size (in bytes) the WAL archive can occupy on the file system.</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Four times the size of the <a href="/docs/latest/persistence/persistence-tuning#adjusting-checkpointing-buffer-size">checkpointing buffer</a>.</p></td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="copyright">
© 2021 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>
<nav class="right-nav" data-swiftype-index='false'>
<div class="toc-wrapper">
<ul class="sectlevel1">
<li><a href="#overview">Overview</a></li>
<li><a href="#enabling-persistent-storage">Enabling Persistent Storage</a></li>
<li><a href="#configuring-persistent-storage-directory">Configuring Persistent Storage Directory</a></li>
<li><a href="#write-ahead-log">Write-Ahead Log</a>
<ul class="sectlevel2">
<li><a href="#wal-modes">WAL Modes</a></li>
<li><a href="#wal-archive">WAL Archive</a></li>
<li><a href="#changing-wal-segment-size">Changing WAL Segment Size</a></li>
<li><a href="#disabling-wal">Disabling WAL</a></li>
<li><a href="#wal-archive-compaction">WAL Archive Compaction</a></li>
<li><a href="#wal-records-compression">WAL Records Compression</a></li>
<li><a href="#disabling-wal-archive">Disabling WAL Archive</a></li>
</ul>
</li>
<li><a href="#checkpointing">Checkpointing</a></li>
<li><a href="#configuration-properties">Configuration Properties</a></li>
</ul>
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