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<!DOCTYPE concept
  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<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>