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| <title>Peristence - Apache Ignite</title> |
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| <main id="main" role="main" class="container"> |
| <section id="native-persistence" class="page-section"> |
| <h1 class="first">Ignite Native Persistence</h1> |
| <div class="col-sm-12 col-md-12 col-xs-12" style="padding-left:0; padding-right:0;"> |
| <div class="col-sm-6 col-md-6 col-xs-12" style="padding-left:0; padding-right:0;"> |
| <p> |
| As it is covered in <a href="/arch/memorycentric.html">memory-centric storage</a>, |
| Ignite is widely used as a caching layer (aka. data grid) above an existing 3rd |
| party database such as RDBMS, Apache Cassandra or MongoDB. This mode is used to |
| accelerate the underlying database that persists the data. |
| At the same time Ignite comes with its own persistence, that is considered as an alternate |
| and preferable persistence layer for the Ignite cluster. |
| </p> |
| <p> |
| Ignite native persistence is a distributed, ACID, and <nobr>SQL-compliant</nobr> disk store |
| that transparently integrates with Ignite's durable memory. Ignite persistence is optional |
| and can be turned on and off. When turned off Ignite becomes a pure in-memory store. |
| </p> |
| </div> |
| <div class="col-sm-6 col-md-6 col-xs-12" style="padding-right:0; top: -10px;"> |
| <a href="/images/native_persistence.png"><img class="img-responsive" src="/images/native_persistence.png" width="450px" style="float:right;" alt="Apache Ignite Native Persistence - Distributed SQL Database"/></a> |
| </div> |
| </div> |
| <p> |
| With the the native persistence enabled, Ignite always stores a superset of data on disk, |
| and as much as possible in RAM. For example, if there are |
| 100 entries and RAM has the capacity to store only 20, then all 100 will be stored on disk |
| and only 20 will be cached in RAM for better performance. |
| </p> |
| |
| <p> |
| The native persistence has the following important characteristics: |
| </p> |
| <ul class="page-list" style="margin-bottom: 20px;"> |
| <li> |
| SQL queries over the full data set that spans both, memory and disk. This means that Apache |
| Ignite can be used as a memory-centric distributed SQL database. |
| </li> |
| <li> |
| No need to have all the data in memory. Ignite persistence allows storing a superset |
| of data on disk and only most frequently used subsets in memory. |
| </li> |
| <li> |
| Instantaneous cluster restarts. Ignite becomes fully operational from disk immediately |
| upon cluster startup or restart. There is no need to preload or warm up the in-memory caches. |
| The data will be loaded in-memory lazily, as it gets accessed. |
| </li> |
| <li> |
| Data and indexes are stored in a similar format both in memory and on disk, which helps avoid |
| expensive transformations when moving data between memory and disk. |
| </li> |
| <li> |
| Ability to create full and incremental cluster snapshots by plugging-in 3rd party solutions. |
| </li> |
| </ul> |
| |
| <div class="page-heading">Write-Ahead Log</div> |
| <p> |
| Every time the data is updated in memory, the update will be appended to the tail of |
| the write-ahead log (WAL). The purpose of the WAL is to propagate updates to disk in |
| the fastest way possible and provide a consistent recovery mechanism that supports full cluster failures. |
| </p> |
| <p> |
| The whole WAL is split into several files, called segments, that are filled out sequentially. |
| Once a segment is full, its content will be copied to the <i>WAL archive</i> where it will be preserved |
| for a configurable amount of time. While the segment is being copied, another segment |
| will be treated as an active WAL file. |
| </p> |
| <p> |
| The cluster can always be recovered up to the latest successfully committed transaction. |
| </p> |
| |
| <div class="page-heading">Checkpointing</div> |
| <p> |
| As WAL grows, it periodically gets <i>checkpointed</i> to the main storage. |
| The checkpointing is the process of copying <i>dirty pages</i> from memory to the partition files on disk. |
| A dirty page is a page that was updated in memory, was appended to WAL, but was not written to a respective partition |
| file on disk yet. |
| </p> |
| <div class="page-heading">Durability</div> |
| <p> |
| Ignite native persistence provides ACID durability guarantees to the data: |
| |
| <ul class="page-list" style="margin-bottom: 20px;"> |
| <li>Committed transactions will always survive any failures.</li> |
| <li> |
| The cluster can always be recovered to the latest successfully committed transaction. |
| </li> |
| <li> |
| The cluster restarts are very fast. |
| </li> |
| </ul> |
| </p> |
| <div class="page-heading">Configuration</div> |
| <p> |
| To enable Ignite persistence, add the following configuration parameter to the cluster's |
| node configuration: |
| </p> |
| <div class="tab-content"> |
| <div class="tab-pane active" id="configuration"> |
| <pre class="brush:xml"> |
| <bean class="org.apache.ignite.configuration.IgniteConfiguration"> |
| <!-- Enabling Apache Ignite native persistence. --> |
| <property name="dataStorageConfiguration"> |
| <bean class="org.apache.ignite.configuration.DataStorageConfiguration"> |
| <property name="defaultDataRegionConfiguration"> |
| <bean class="org.apache.ignite.configuration.DataRegionConfiguration"> |
| <property name="persistenceEnabled" value="true"/> |
| </bean> |
| </property> |
| </bean> |
| </property> |
| |
| <!-- Additional setting. --> |
| |
| </bean> |
| </pre> |
| </div> |
| </div> |
| <p><a href="https://apacheignite.readme.io/docs/distributed-persistent-store" target="_blank">Read more</a></p> |
| </section> |
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