Symbian3/PDK/Source/GUID-2FAB8281-569A-52BE-8BC8-A2D378068706.dita
author Dominic Pinkman <Dominic.Pinkman@Nokia.com>
Fri, 22 Jan 2010 18:26:19 +0000
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permissions -rw-r--r--
Addition of the PDK content and example code for Documentation_content according to Feature bug 1607 and bug 1608
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<?xml version="1.0" encoding="utf-8"?>
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<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
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<!-- This component and the accompanying materials are made available under the terms of the License 
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"Eclipse Public License v1.0" which accompanies this distribution, 
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and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
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<!-- Initial Contributors:
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    Nokia Corporation - initial contribution.
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Contributors: 
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-->
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<!DOCTYPE concept
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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
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<concept id="GUID-2FAB8281-569A-52BE-8BC8-A2D378068706" xml:lang="en"><title>Caching</title><prolog><metadata><keywords/></metadata></prolog><conbody>
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<p>In Symbian OS versions earlier than 9.4, index entries were stored in a
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single index file in a permanent file store and the entire file was loaded
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into RAM on start up. In Symbian OS version 9.5 index entries are stored in
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an SQL database and only the most recently used index entries are cached in
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RAM. </p>
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<p>The following figure shows how a client request is completed using the
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cache functionality in the Message Server. </p>
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<fig id="GUID-43D2AE30-9221-500A-B934-5D3636168273">
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<title>           Caching architecture          </title>
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<image href="GUID-53A2CA11-2ABF-5ED7-A26C-7BE9FD9A1D22_d0e471529_href.png" placement="inline"/>
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</fig>
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<section><title>Creating and maintaining free space in memory</title> <p>Memory
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allocation to the cache is done incrementally, to reduce the Message Server
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start up time. When the Message Server starts, only a percentage of the maximum
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cache size (<codeph>MsvMaximumCacheSize</codeph>) is allocated to cache. The
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percentage is specified by the <codeph>MsvInitialCacheCreation</codeph> parameter.
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The next iteration of memory allocation is not initiated until the memory
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threshold (set using the <codeph>MsvCacheThreshold</codeph> parameter) is
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reached. The subsequent memory allocation is always done by a low priority
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active object. </p> <p><b>Example</b> </p> <p>The memory allocation strategy
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is illustrated in the following figures, based on the default values (shown
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in the preceding table). </p> <p>When Message Server starts, the cache is
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created with an initial size of 410KB (40 percent of 1024KB). If 70 percent
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of the free space in the cache gets used the server allocates an additional
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205KB (20 percent of 1024). </p> <fig id="GUID-CA4A08C8-C4E8-575F-8F03-F3D1F6579E5F">
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<image href="GUID-B459E37A-BECE-5087-9827-C93310890674_d0e471561_href.png" placement="inline"/>
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</fig> <p>Message Server can make two further 205KB allocations which it does
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as use reaches 70 percent of the memory already allocated. </p> <fig id="GUID-21A40614-046B-56DD-9DDD-34B2F9681B5C">
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<image href="GUID-107F7BC4-F776-512D-AD6F-1674B7ED19B5_d0e471569_href.png" placement="inline"/>
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</fig> <p>If more than 70 percent of the first two allocated memory chunks
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is used, an additional 20 percent of memory is added to the free space. </p> <fig id="GUID-EBF4FF85-D6D6-518C-9391-C3AFF8821F83">
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<image href="GUID-5E380880-9DBB-51D7-8942-829C6FD788C2_d0e471577_href.png" placement="inline"/>
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</fig> </section>
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</conbody></concept>