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| <title>MRUMemoryStore and Swapping under Apache Cocoon</title> |
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| <meta content="Gerhard Froehlich" name="DC.Creator"> |
| <meta content="This document explains how the MRUMemoryStore and Swapping under |
| Cocoon executes." name="DC.Description"> |
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| |
| <h1>Goal</h1> |
| |
| <p>This document explains how the MRUMemoryStore and Swapping under |
| Cocoon executes.</p> |
| |
| |
| <h1>Overview</h1> |
| |
| <p>The MRUMemoryStore was developed to provide a standard algorithm to |
| store data in memory. For web-based applications the MRU (Most Recently Used) algorithm |
| is very suitable, because the object most frequently accessed is always on "top". |
| </p> |
| |
| <p>If configured, the objects are also swapped to the filesystem if the |
| MRUMemoryStore reached its configured maximum object limit. |
| </p> |
| |
| |
| <h1>Implementation</h1> |
| |
| <h2>MRUMemoryStore</h2> |
| <p> |
| The heart of the MRUMemoryStore is a combination of a LinkedList and a HashMap: |
| </p> |
| <p> |
| The LinkedList provides the queue mechanism, and the entries in the LinkedList |
| contain the key to the data in the HashMap. When caching a new entry in to the list, |
| the entry is inserted to the front of the list. |
| If the list is already full, the oldest data entry is removed from the Cache. |
| When requesting a entry, the store returns the object by key and inserts the requested key |
| on the top of the Cache. |
| |
| This implementation keeps the most recent used objects in the store and provides the best |
| use of the machines memory. |
| </p> |
| |
| <h2>Swapping</h2> |
| <p> |
| When the MRUMemoryStore is full or the JVM is at the heap size limit the |
| objects in the MRUMemoryStore are swapped to the Filesystem. The default |
| directory is "cache-dir" in the work-directory. |
| </p> |
| <p> |
| NOTE: The keys under Cocoon are Strings at the moment. Therefore the |
| filenames of the swapped objects can be very long. Especially Windows OS |
| flavours have problems with long filenames. Use the JispFilesystemStore to |
| deal with that (see <a href="persistence.html">Persistent cache</a>). |
| </p> |
| |
| |
| <h1>Configuration of the MRUMemoryStore in the cocoon.xconf</h1> |
| |
| <pre class="code"> |
| <store logger="core.store"> |
| <parameter name="maxobjects" value="100"/> |
| <parameter name="use-persistent-cache" value="true"/> |
| </store> |
| </pre> |
| |
| <p>Explanation of the parameters:</p> |
| |
| <ol> |
| |
| <li> |
| <span class="codefrag"><parameter name="maxobjects" value="100"/></span>: |
| Indicates how many objects will be held in MRUMemoryStore. When the number |
| of maxobjects has been reached, the last object in the MRUMemoryStore will be |
| thrown out.</li> |
| |
| <li> |
| <span class="codefrag"><parameter name="use-persistent-cache" value="true"/></span>: |
| If this switch is set on true, objects are swapped out to the filesystem, |
| if the MRUMemoryStore has reached its maximum object limit, or the JVM |
| memory consumption is over the heap size limit. See StoreJanitor user |
| docs for more information.</li> |
| |
| </ol> |
| |
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