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<div class="section" id="distributed-key-value-store">
<span id="distributed-key-value-store"></span><h1>Distributed Key-Value Store<a class="headerlink" href="#distributed-key-value-store" title="Permalink to this headline"></a></h1>
<p>KVStore is a place for data sharing. Think of it as a single object shared
across different devices (GPUs and computers), where each device can push data in
and pull data out.</p>
<div class="section" id="initialization">
<span id="initialization"></span><h2>Initialization<a class="headerlink" href="#initialization" title="Permalink to this headline"></a></h2>
<p>Let’s consider a simple example: initializing
a (<code class="docutils literal"><span class="pre">int</span></code>, <code class="docutils literal"><span class="pre">NDArray</span></code>) pair into the store, and then pulling the value out:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span> <span class="o">>>></span> <span class="n">kv</span> <span class="o">=</span> <span class="n">mx</span><span class="o">.</span><span class="n">kv</span><span class="o">.</span><span class="n">create</span><span class="p">(</span><span class="s1">'local'</span><span class="p">)</span> <span class="c1"># create a local kv store.</span>
<span class="o">>>></span> <span class="n">shape</span> <span class="o">=</span> <span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">init</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">mx</span><span class="o">.</span><span class="n">nd</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="n">shape</span><span class="p">)</span><span class="o">*</span><span class="mi">2</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">a</span> <span class="o">=</span> <span class="n">mx</span><span class="o">.</span><span class="n">nd</span><span class="o">.</span><span class="n">zeros</span><span class="p">(</span><span class="n">shape</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">pull</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">out</span> <span class="o">=</span> <span class="n">a</span><span class="p">)</span>
<span class="o">>>></span> <span class="k">print</span> <span class="n">a</span><span class="o">.</span><span class="n">asnumpy</span><span class="p">()</span>
<span class="p">[[</span> <span class="mf">2.</span> <span class="mf">2.</span> <span class="mf">2.</span><span class="p">]</span>
<span class="p">[</span> <span class="mf">2.</span> <span class="mf">2.</span> <span class="mf">2.</span><span class="p">]]</span>
</pre></div>
</div>
</div>
<div class="section" id="push-aggregate-and-update">
<span id="push-aggregate-and-update"></span><h2>Push, Aggregate, and Update<a class="headerlink" href="#push-aggregate-and-update" title="Permalink to this headline"></a></h2>
<p>For any key that has been initialized, you can push a new value with the same shape to the key:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span> <span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">push</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">mx</span><span class="o">.</span><span class="n">nd</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="n">shape</span><span class="p">)</span><span class="o">*</span><span class="mi">8</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">pull</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">out</span> <span class="o">=</span> <span class="n">a</span><span class="p">)</span> <span class="c1"># pull out the value</span>
<span class="o">>>></span> <span class="k">print</span> <span class="n">a</span><span class="o">.</span><span class="n">asnumpy</span><span class="p">()</span>
<span class="p">[[</span> <span class="mf">8.</span> <span class="mf">8.</span> <span class="mf">8.</span><span class="p">]</span>
<span class="p">[</span> <span class="mf">8.</span> <span class="mf">8.</span> <span class="mf">8.</span><span class="p">]]</span>
</pre></div>
</div>
<p>The data for pushing can be stored on any device. Furthermore, you can push multiple
values into the same key, where KVStore will first sum all of these
values and then push the aggregated value:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span> <span class="o">>>></span> <span class="n">gpus</span> <span class="o">=</span> <span class="p">[</span><span class="n">mx</span><span class="o">.</span><span class="n">gpu</span><span class="p">(</span><span class="n">i</span><span class="p">)</span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">4</span><span class="p">)]</span>
<span class="o">>>></span> <span class="n">b</span> <span class="o">=</span> <span class="p">[</span><span class="n">mx</span><span class="o">.</span><span class="n">nd</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="n">shape</span><span class="p">,</span> <span class="n">gpu</span><span class="p">)</span> <span class="k">for</span> <span class="n">gpu</span> <span class="ow">in</span> <span class="n">gpus</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">push</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">b</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">pull</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">out</span> <span class="o">=</span> <span class="n">a</span><span class="p">)</span>
<span class="o">>>></span> <span class="k">print</span> <span class="n">a</span><span class="o">.</span><span class="n">asnumpy</span><span class="p">()</span>
<span class="p">[[</span> <span class="mf">4.</span> <span class="mf">4.</span> <span class="mf">4.</span><span class="p">]</span>
<span class="p">[</span> <span class="mf">4.</span> <span class="mf">4.</span> <span class="mf">4.</span><span class="p">]]</span>
</pre></div>
</div>
<p>For each push, KVStore combines the pushed value with the value stored using an
<code class="docutils literal"><span class="pre">updater</span></code>. The default updater is <code class="docutils literal"><span class="pre">ASSIGN</span></code>. You can replace the default to
control how data is merged:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span> <span class="o">>>></span> <span class="k">def</span> <span class="nf">update</span><span class="p">(</span><span class="n">key</span><span class="p">,</span> <span class="nb">input</span><span class="p">,</span> <span class="n">stored</span><span class="p">):</span>
<span class="o">>>></span> <span class="k">print</span> <span class="s2">"update on key: </span><span class="si">%d</span><span class="s2">"</span> <span class="o">%</span> <span class="n">key</span>
<span class="o">>>></span> <span class="n">stored</span> <span class="o">+=</span> <span class="nb">input</span> <span class="o">*</span> <span class="mi">2</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">_set_updater</span><span class="p">(</span><span class="n">update</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">pull</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">out</span><span class="o">=</span><span class="n">a</span><span class="p">)</span>
<span class="o">>>></span> <span class="k">print</span> <span class="n">a</span><span class="o">.</span><span class="n">asnumpy</span><span class="p">()</span>
<span class="p">[[</span> <span class="mf">4.</span> <span class="mf">4.</span> <span class="mf">4.</span><span class="p">]</span>
<span class="p">[</span> <span class="mf">4.</span> <span class="mf">4.</span> <span class="mf">4.</span><span class="p">]]</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">push</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">mx</span><span class="o">.</span><span class="n">nd</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="n">shape</span><span class="p">))</span>
<span class="n">update</span> <span class="n">on</span> <span class="n">key</span><span class="p">:</span> <span class="mi">3</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">pull</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">out</span><span class="o">=</span><span class="n">a</span><span class="p">)</span>
<span class="o">>>></span> <span class="k">print</span> <span class="n">a</span><span class="o">.</span><span class="n">asnumpy</span><span class="p">()</span>
<span class="p">[[</span> <span class="mf">6.</span> <span class="mf">6.</span> <span class="mf">6.</span><span class="p">]</span>
<span class="p">[</span> <span class="mf">6.</span> <span class="mf">6.</span> <span class="mf">6.</span><span class="p">]]</span>
</pre></div>
</div>
</div>
<div class="section" id="pull">
<span id="pull"></span><h2>Pull<a class="headerlink" href="#pull" title="Permalink to this headline"></a></h2>
<p>You’ve already seen how to pull a single key-value pair. Similarly, to push, you can
pull the value onto several devices with a single call:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span> <span class="o">>>></span> <span class="n">b</span> <span class="o">=</span> <span class="p">[</span><span class="n">mx</span><span class="o">.</span><span class="n">nd</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="n">shape</span><span class="p">,</span> <span class="n">gpu</span><span class="p">)</span> <span class="k">for</span> <span class="n">gpu</span> <span class="ow">in</span> <span class="n">gpus</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">pull</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">out</span> <span class="o">=</span> <span class="n">b</span><span class="p">)</span>
<span class="o">>>></span> <span class="k">print</span> <span class="n">b</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="o">.</span><span class="n">asnumpy</span><span class="p">()</span>
<span class="p">[[</span> <span class="mf">6.</span> <span class="mf">6.</span> <span class="mf">6.</span><span class="p">]</span>
<span class="p">[</span> <span class="mf">6.</span> <span class="mf">6.</span> <span class="mf">6.</span><span class="p">]]</span>
</pre></div>
</div>
</div>
<div class="section" id="handle-a-list-of-key-value-pairs">
<span id="handle-a-list-of-key-value-pairs"></span><h2>Handle a List of Key-Value Pairs<a class="headerlink" href="#handle-a-list-of-key-value-pairs" title="Permalink to this headline"></a></h2>
<p>All operations introduced so far involve a single key. KVStore also provides
an interface for a list of key-value pairs.</p>
<p>For a single device:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span> <span class="o">>>></span> <span class="n">keys</span> <span class="o">=</span> <span class="p">[</span><span class="mi">5</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">9</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">init</span><span class="p">(</span><span class="n">keys</span><span class="p">,</span> <span class="p">[</span><span class="n">mx</span><span class="o">.</span><span class="n">nd</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="n">shape</span><span class="p">)]</span><span class="o">*</span><span class="nb">len</span><span class="p">(</span><span class="n">keys</span><span class="p">))</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">push</span><span class="p">(</span><span class="n">keys</span><span class="p">,</span> <span class="p">[</span><span class="n">mx</span><span class="o">.</span><span class="n">nd</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="n">shape</span><span class="p">)]</span><span class="o">*</span><span class="nb">len</span><span class="p">(</span><span class="n">keys</span><span class="p">))</span>
<span class="n">update</span> <span class="n">on</span> <span class="n">key</span><span class="p">:</span> <span class="mi">5</span>
<span class="n">update</span> <span class="n">on</span> <span class="n">key</span><span class="p">:</span> <span class="mi">7</span>
<span class="n">update</span> <span class="n">on</span> <span class="n">key</span><span class="p">:</span> <span class="mi">9</span>
<span class="o">>>></span> <span class="n">b</span> <span class="o">=</span> <span class="p">[</span><span class="n">mx</span><span class="o">.</span><span class="n">nd</span><span class="o">.</span><span class="n">zeros</span><span class="p">(</span><span class="n">shape</span><span class="p">)]</span><span class="o">*</span><span class="nb">len</span><span class="p">(</span><span class="n">keys</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">pull</span><span class="p">(</span><span class="n">keys</span><span class="p">,</span> <span class="n">out</span> <span class="o">=</span> <span class="n">b</span><span class="p">)</span>
<span class="o">>>></span> <span class="k">print</span> <span class="n">b</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="o">.</span><span class="n">asnumpy</span><span class="p">()</span>
<span class="p">[[</span> <span class="mf">3.</span> <span class="mf">3.</span> <span class="mf">3.</span><span class="p">]</span>
<span class="p">[</span> <span class="mf">3.</span> <span class="mf">3.</span> <span class="mf">3.</span><span class="p">]]</span>
</pre></div>
</div>
<p>For multiple devices:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span> <span class="o">>>></span> <span class="n">b</span> <span class="o">=</span> <span class="p">[[</span><span class="n">mx</span><span class="o">.</span><span class="n">nd</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="n">shape</span><span class="p">,</span> <span class="n">gpu</span><span class="p">)</span> <span class="k">for</span> <span class="n">gpu</span> <span class="ow">in</span> <span class="n">gpus</span><span class="p">]]</span> <span class="o">*</span> <span class="nb">len</span><span class="p">(</span><span class="n">keys</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">push</span><span class="p">(</span><span class="n">keys</span><span class="p">,</span> <span class="n">b</span><span class="p">)</span>
<span class="n">update</span> <span class="n">on</span> <span class="n">key</span><span class="p">:</span> <span class="mi">5</span>
<span class="n">update</span> <span class="n">on</span> <span class="n">key</span><span class="p">:</span> <span class="mi">7</span>
<span class="n">update</span> <span class="n">on</span> <span class="n">key</span><span class="p">:</span> <span class="mi">9</span>
<span class="o">>>></span> <span class="n">kv</span><span class="o">.</span><span class="n">pull</span><span class="p">(</span><span class="n">keys</span><span class="p">,</span> <span class="n">out</span> <span class="o">=</span> <span class="n">b</span><span class="p">)</span>
<span class="o">>>></span> <span class="k">print</span> <span class="n">b</span><span class="p">[</span><span class="mi">1</span><span class="p">][</span><span class="mi">1</span><span class="p">]</span><span class="o">.</span><span class="n">asnumpy</span><span class="p">()</span>
<span class="p">[[</span> <span class="mf">11.</span> <span class="mf">11.</span> <span class="mf">11.</span><span class="p">]</span>
<span class="p">[</span> <span class="mf">11.</span> <span class="mf">11.</span> <span class="mf">11.</span><span class="p">]]</span>
</pre></div>
</div>
</div>
<div class="section" id="run-on-multiple-machines">
<span id="run-on-multiple-machines"></span><h2>Run on Multiple Machines<a class="headerlink" href="#run-on-multiple-machines" title="Permalink to this headline"></a></h2>
<p>Based on parameter server, the <code class="docutils literal"><span class="pre">updater</span></code> runs on the server nodes.
When the distributed version is ready, we will update this section.</p>
<!-- ## How to Choose Between APIs --><!-- You can mix APIs as much as you like. Here are some guidelines -->
<!-- * Use the Symbolic API and a coarse-grained operator to create an established structure. -->
<!-- * Use a fine-grained operator to extend parts of a more flexible symbolic graph. -->
<!-- * Do some dynamic NDArray tricks, which are even more flexible, between the calls of forward and backward executors. --><!-- Different approaches offer you different levels of flexibility and -->
<!-- efficiency. Normally, you do not need to be flexible in all parts of the -->
<!-- network, so use the parts optimized for speed, and compose it -->
<!-- flexibly with a fine-grained operator or a dynamic NDArray. Such a -->
<!-- mixture allows you to build the deep learning architecture both efficiently and -->
<!-- flexibly as your choice. --></div>
<div class="section" id="next-steps">
<span id="next-steps"></span><h2>Next Steps<a class="headerlink" href="#next-steps" title="Permalink to this headline"></a></h2>
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<li class="toctree-l1"><a class="reference external" href="https://mxnet.incubator.apache.org/tutorials/index.html">MXNet tutorials index</a></li>
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<h3><a href="../../index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Distributed Key-Value Store</a><ul>
<li><a class="reference internal" href="#initialization">Initialization</a></li>
<li><a class="reference internal" href="#push-aggregate-and-update">Push, Aggregate, and Update</a></li>
<li><a class="reference internal" href="#pull">Pull</a></li>
<li><a class="reference internal" href="#handle-a-list-of-key-value-pairs">Handle a List of Key-Value Pairs</a></li>
<li><a class="reference internal" href="#run-on-multiple-machines">Run on Multiple Machines</a></li>
<li><a class="reference internal" href="#next-steps">Next Steps</a></li>
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