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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-2FAB8281-569A-52BE-8BC8-A2D378068706" xml:lang="en"><title>Caching</title><prolog><metadata><keywords/></metadata></prolog><conbody>

    13 <p>In Symbian OS versions earlier than 9.4, index entries were stored in a

    14 single index file in a permanent file store and the entire file was loaded

    15 into RAM on start up. In Symbian OS version 9.5 index entries are stored in

    16 an SQL database and only the most recently used index entries are cached in

    17 RAM. </p>

    18 <p>The following figure shows how a client request is completed using the

    19 cache functionality in the Message Server. </p>

    20 <fig id="GUID-43D2AE30-9221-500A-B934-5D3636168273">

    21 <title>           Caching architecture          </title>

    22 <image href="GUID-53A2CA11-2ABF-5ED7-A26C-7BE9FD9A1D22_d0e256631_href.png" placement="inline"/>

    23 </fig>

    24 <section><title>Creating and maintaining free space in memory</title> <p>Memory

    25 allocation to the cache is done incrementally, to reduce the Message Server

    26 start up time. When the Message Server starts, only a percentage of the maximum

    27 cache size (<codeph>MsvMaximumCacheSize</codeph>) is allocated to cache. The

    28 percentage is specified by the <codeph>MsvInitialCacheCreation</codeph> parameter.

    29 The next iteration of memory allocation is not initiated until the memory

    30 threshold (set using the <codeph>MsvCacheThreshold</codeph> parameter) is

    31 reached. The subsequent memory allocation is always done by a low priority

    32 active object. </p> <p><b>Example</b> </p> <p>The memory allocation strategy

    33 is illustrated in the following figures, based on the default values (shown

    34 in the preceding table). </p> <p>When Message Server starts, the cache is

    35 created with an initial size of 410KB (40 percent of 1024KB). If 70 percent

    36 of the free space in the cache gets used the server allocates an additional

    37 205KB (20 percent of 1024). </p> <fig id="GUID-CA4A08C8-C4E8-575F-8F03-F3D1F6579E5F">

    38 <image href="GUID-B459E37A-BECE-5087-9827-C93310890674_d0e256663_href.png" placement="inline"/>

    39 </fig> <p>Message Server can make two further 205KB allocations which it does

    40 as use reaches 70 percent of the memory already allocated. </p> <fig id="GUID-21A40614-046B-56DD-9DDD-34B2F9681B5C">

    41 <image href="GUID-107F7BC4-F776-512D-AD6F-1674B7ED19B5_d0e256671_href.png" placement="inline"/>

    42 </fig> <p>If more than 70 percent of the first two allocated memory chunks

    43 is used, an additional 20 percent of memory is added to the free space. </p> <fig id="GUID-EBF4FF85-D6D6-518C-9391-C3AFF8821F83">

    44 <image href="GUID-5E380880-9DBB-51D7-8942-829C6FD788C2_d0e256679_href.png" placement="inline"/>

    45 </fig> </section>

    46 </conbody></concept>