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   <div class="section" id="singa-architecture">
 <span id="singa-architecture"></span><h1>SINGA Architecture<a class="headerlink" href="#singa-architecture" title="Permalink to this headline">¶</a></h1>
 <hr class="docutils" />
 <div class="section" id="logical-architecture">
 <span id="logical-architecture"></span><h2>Logical Architecture<a class="headerlink" href="#logical-architecture" title="Permalink to this headline">¶</a></h2>
 <p><img src="../_static/images/logical.png" style="width: 550px"/></p>
 <p><strong> Fig.1 - Logical system architecture</strong></p><p>SINGA has flexible architecture to support different distributed
 <a class="reference external" href="frameworks.html">training frameworks</a> (both synchronous and asynchronous).
 The logical system architecture is shown in Fig.1.
 The architecture consists of multiple server groups and worker groups:</p>
 <ul class="simple">
 <li><strong>Server group</strong>
 A server group maintains a complete replica of the model parameters,
 and is responsible for handling get/update requests from worker groups.
 Neighboring server groups synchronize their parameters periodically.
 Typically, a server group contains a number of servers,
 and each server manages a partition of model parameters.</li>
 <li><strong>Worker group</strong>
 Each worker group communicates with only one server group.
 A worker group trains a complete model replica
 against a partition of the training dataset,
 and is responsible for computing parameter gradients.
 All worker groups run and communicate with the corresponding
 server groups asynchronously.
 However, inside each worker group,
 the workers synchronously compute parameter updates for the model replica.</li>
 </ul>
 <p>There are different strategies to distribute the training workload among workers
 within a group:</p>
 <ul class="simple">
 <li><strong>Model parallelism</strong>. Each worker computes a subset of parameters
 against all data partitioned to the group.</li>
 <li><strong>Data parallelism</strong>. Each worker computes all parameters
 against a subset of data.</li>
 <li><a class="reference external" href="hybrid.html"><strong>Hybrid parallelism</strong></a>. SINGA also supports hybrid parallelism.</li>
 </ul>
 </div>
 <div class="section" id="implementation">
 <span id="implementation"></span><h2>Implementation<a class="headerlink" href="#implementation" title="Permalink to this headline">¶</a></h2>
 <p>In SINGA, servers and workers are execution units running in separate threads.
 They communicate through <a class="reference external" href="communication.html">messages</a>.
 Every process runs the main thread as a stub that aggregates local messages
 and forwards them to corresponding (remote) receivers.</p>
 <p>Each server group and worker group have a <em>ParamShard</em>
 object representing a complete model replica. If workers and servers
 resident in the same process, their <em>ParamShard</em> (partitions) can
 be configured to share the same memory space. In this case, the
 messages transferred between different execution units just contain
 pointers to the data, which reduces the communication cost.
 Unlike in inter-process cases,
 the messages have to include the parameter values.</p>
 </div>
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	<div class="section" id="singa-architecture">
	<span id="singa-architecture"></span><h1>SINGA Architecture<a class="headerlink" href="#singa-architecture" title="Permalink to this headline">¶</a></h1>
	<hr class="docutils" />
	<div class="section" id="logical-architecture">
	<span id="logical-architecture"></span><h2>Logical Architecture<a class="headerlink" href="#logical-architecture" title="Permalink to this headline">¶</a></h2>
	<p><img src="../_static/images/logical.png" style="width: 550px"/></p>
	<p><strong> Fig.1 - Logical system architecture</strong></p><p>SINGA has flexible architecture to support different distributed
	<a class="reference external" href="frameworks.html">training frameworks</a> (both synchronous and asynchronous).
	The logical system architecture is shown in Fig.1.
	The architecture consists of multiple server groups and worker groups:</p>
	<ul class="simple">
	<li><strong>Server group</strong>
	A server group maintains a complete replica of the model parameters,
	and is responsible for handling get/update requests from worker groups.
	Neighboring server groups synchronize their parameters periodically.
	Typically, a server group contains a number of servers,
	and each server manages a partition of model parameters.</li>
	<li><strong>Worker group</strong>
	Each worker group communicates with only one server group.
	A worker group trains a complete model replica
	against a partition of the training dataset,
	and is responsible for computing parameter gradients.
	All worker groups run and communicate with the corresponding
	server groups asynchronously.
	However, inside each worker group,
	the workers synchronously compute parameter updates for the model replica.</li>
	</ul>
	<p>There are different strategies to distribute the training workload among workers
	within a group:</p>
	<ul class="simple">
	<li><strong>Model parallelism</strong>. Each worker computes a subset of parameters
	against all data partitioned to the group.</li>
	<li><strong>Data parallelism</strong>. Each worker computes all parameters
	against a subset of data.</li>
	<li><a class="reference external" href="hybrid.html"><strong>Hybrid parallelism</strong></a>. SINGA also supports hybrid parallelism.</li>
	</ul>
	</div>
	<div class="section" id="implementation">
	<span id="implementation"></span><h2>Implementation<a class="headerlink" href="#implementation" title="Permalink to this headline">¶</a></h2>
	<p>In SINGA, servers and workers are execution units running in separate threads.
	They communicate through <a class="reference external" href="communication.html">messages</a>.
	Every process runs the main thread as a stub that aggregates local messages
	and forwards them to corresponding (remote) receivers.</p>
	<p>Each server group and worker group have a <em>ParamShard</em>
	object representing a complete model replica. If workers and servers
	resident in the same process, their <em>ParamShard</em> (partitions) can
	be configured to share the same memory space. In this case, the
	messages transferred between different execution units just contain
	pointers to the data, which reduces the communication cost.
	Unlike in inter-process cases,
	the messages have to include the parameter values.</p>
	</div>
	</div>


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	© Copyright 2016 The Apache Software Foundation. All rights reserved. Apache Singa, Apache, the Apache feather logo, and the Apache Singa project logos are trademarks of The Apache Software Foundation. All other marks mentioned may be trademarks or registered trademarks of their respective owners..

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