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| <title>Memory-Centric Storage - Apache Ignite</title> |
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| content="Apache Ignite memory-centric storage uses both memory and disk as active storage tiers. Speed of |
| memory with the consistency of disk-based databases and no need for memory warm-ups on restarts."/> |
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| <main id="main" role="main" class="container"> |
| <section id="memory-centric" class="page-section"> |
| <h1 class="first">Memory-Centric Storage</h1> |
| <div class="col-sm-12 col-md-12 col-xs-12" style="padding:0 0 20px 0;"> |
| <div class="col-sm-6 col-md-6 col-xs-12" style="padding-left:0; padding-right:0"> |
| <p> |
| Apache Ignite is designed to work with both memory and disk as active storage tiers. |
| Ignite storage is classified as a memory-centric one since most of the architectural decisions |
| favor specificities of the memory tier that is always at use and cannot be disabled. |
| The disk tier is optional with the support of two options -- you can persist data in an |
| external database or keep it in the Ignite native persistence. |
| </p> |
| </div> |
| <div class="col-sm-6 col-md-6 col-xs-12" style="padding-right:0"> |
| <img class="img-responsive" src="/images/durable_memory.png" width="440px" style="float: right;"/> |
| </div> |
| </div> |
| <p> |
| Ignite takes full control of its memory tier by allocating and managing off-heap regions. Each Ignite |
| server node allocates memory regions during bootstrap, splits the regions into pages, and keeps data |
| records with indexes there. Java heap is used to keep temporary objects such as queries results sets, |
| metrics samples, objects generated by your application code. All these objects are garbage collected |
| eventually. |
| </p> |
| <p> |
| If you select the native persistence as the disk tier, then most of the processing will still |
| take place in memory on cached data, but, with a full copy stored on disk. If any record is |
| missing in memory, Ignite will read it from disk, allowing you to persist much larger data sets |
| than you can cache in memory. That also eliminates the need for time-consuming memory warm-ups |
| on restarts. As soon as your cluster reconnects after a restart, Ignite will serve most of the |
| data from disk warming the memory tier up in the background. |
| </p> |
| |
| <div class="page-heading" id="storage-usage-modes"> |
| Memory-Centric Storage Usage Modes |
| <a href="/arch/memorycentric.html#storage-usage-modes"><i class="fa fa-anchor"></i></a> |
| </div> |
| <p> |
| Below you can see primary modes for memory-centric storage usage and configuration: |
| </p> |
| <table class="formatted" name="Deployment Options Features"> |
| <thead> |
| <tr> |
| <th width="35%" class="left">Mode</th> |
| <th>Description</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td class="left">In-Memory</td> |
| <td> |
| <p> |
| The whole data set is available in memory only. In order to survive node failures, it is |
| recommended to keep at least one backup copy of the data across the cluster. |
| </p> |
| |
| <p> |
| <strong>Use cases</strong>: general in-memory caching, high-performance |
| computing, web-session caching, real-time processing of continuous data streams. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td class="left">In-Memory + External Database</td> |
| <td> |
| <p> |
| Ignite is deployed as a distributed caching layer on top of an existing external database. |
| This mode is for the acceleration of disk-based databases and your services with APIs that |
| interact with them. |
| </p> |
| |
| <p> |
| <strong>Use cases</strong>: acceleration of services and APIs with write-through/behind |
| capability, to an external database (aka. in-memory data grid). |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td class="left">In-Memory Cache + Native Persistence</td> |
| <td> |
| <p> |
| 100% of data is persisted to disk, and the same or smaller amount is cached in memory. |
| The more data is cached, the faster is the performance. The disk serves as the primary |
| storage that survives any cluster failures and restarts. No need for memory warm-ups on |
| restarts as long as Ignite can serve data from disk. |
| </p> |
| |
| <p> |
| <strong>Use cases</strong>: Ignite as an in-memory database or digital integration hub |
| with the active persistence layer. |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| |
| <h2 style="padding-top: 10px;" id="partitioning"> |
| Partitioning & Replication |
| <a href="/arch/memorycentric.html#partitioning"><i class="fa fa-anchor"></i></a> |
| </h2> |
| <p> |
| Depending on the configuration, Ignite can both partition or replicate data across its memory-centric |
| storage. With the replicated mode, each cluster node keeps a full copy of the data that is advantageous |
| for frequently accessed dictionaries. As for the partitioned mode, Ignite spreads the data across all |
| the cluster nodes evenly, allowing to store much more than a single machine can fit in. |
| </p> |
| |
| <h2 style="padding-top: 10px;" id="durability"> |
| Durability and Consistency |
| <a href="/arch/memorycentric.html#durability"><i class="fa fa-anchor"></i></a> |
| </h2> |
| <p> |
| Ignite provides strong ACID durability guarantees to the data: |
| </p> |
| |
| <ul class="page-list" style="margin-bottom: 20px;"> |
| <li>Committed transactions always survive failures.</li> |
| <li> |
| The cluster can always be recovered to the latest successfully committed transaction. |
| </li> |
| </ul> |
| |
| |
| <h2 style="padding-top: 10px;" id="write-ahead-log"> |
| Write-Ahead Logging and Checkpointing |
| <a href="/arch/memorycentric.html#write-ahead-log"><i class="fa fa-anchor"></i></a> |
| </h2> |
| <p> |
| If Ignite native persistence is selected as a disk tier, then every time a record is updated in memory, |
| the change is added to 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> |
| As WAL grows, it periodically gets checkpointed to the main storage. Checkpointing is the process of |
| copying dirty pages from the memory tier 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">Learn More</div> |
| <p> |
| <a href="/arch/persistence.html"> |
| <b>Native Persistence <i class="fa fa-angle-double-right"></i></b> |
| </a> |
| </p> |
| <p> |
| <a href="/features/datagrid.html"> |
| <b>Ignite as an In-Memory Data Grid <i class="fa fa-angle-double-right"></i></b> |
| </a> |
| </p> |
| <p> |
| <a href="/use-cases/in-memory-database.html"> |
| <b>Ignite as an In-Memory Database <i class="fa fa-angle-double-right"></i></b> |
| </a> |
| </p> |
| <p> |
| <a href="/use-cases/dih.html"> |
| <b>Ignite as a Digital Integration Hub <i class="fa fa-angle-double-right"></i></b> |
| </a> |
| </p> |
| <p> |
| <a href="/use-cases/hpc.html"> |
| <b>Ignite for High Performance Computing <i class="fa fa-angle-double-right"></i></b> |
| </a> |
| </p> |
| </section> |
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