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

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

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

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

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

RAM. </p>

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

cache functionality in the Message Server. </p>

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

<title>           Caching architecture          </title>

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

</fig>

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

</fig> </section>

</conbody></concept>