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<div class="section" id="kvstore-api">
<span id="kvstore-api"></span><h1>KVStore API<a class="headerlink" href="#kvstore-api" title="Permalink to this headline"></a></h1>
<p>Topics:</p>
<ul class="simple">
<li><a class="reference external" href="#basic-push-and-pull">Basic Push and Pull</a></li>
<li><a class="reference external" href="#list-key-value-pairs">List Key-Value Pairs</a></li>
<li><a class="reference external" href="https://mxnet.incubator.apache.org/api/scala/docs/index.html#ml.dmlc.mxnet.KVStore">API Reference</a></li>
</ul>
<div class="section" id="basic-push-and-pull">
<span id="basic-push-and-pull"></span><h2>Basic Push and Pull<a class="headerlink" href="#basic-push-and-pull" title="Permalink to this headline"></a></h2>
<p>Provides basic operation over multiple devices (GPUs) on a single device.</p>
<div class="section" id="initialization">
<span id="initialization"></span><h3>Initialization<a class="headerlink" href="#initialization" title="Permalink to this headline"></a></h3>
<p>Let’s consider a simple example. It initializes
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 pulls the value out.</p>
<div class="highlight-scala"><div class="highlight"><pre><span></span> <span class="n">scala</span><span class="o">></span> <span class="k">val</span> <span class="n">kv</span> <span class="k">=</span> <span class="nc">KVStore</span><span class="o">.</span><span class="n">create</span><span class="o">(</span><span class="s">"local"</span><span class="o">)</span> <span class="c1">// create a local kv store.</span>
<span class="n">scala</span><span class="o">></span> <span class="k">val</span> <span class="n">shape</span> <span class="k">=</span> <span class="nc">Shape</span><span class="o">(</span><span class="mi">2</span><span class="o">,</span><span class="mi">3</span><span class="o">)</span>
<span class="n">scala</span><span class="o">></span> <span class="n">kv</span><span class="o">.</span><span class="n">init</span><span class="o">(</span><span class="mi">3</span><span class="o">,</span> <span class="nc">NDArray</span><span class="o">.</span><span class="n">ones</span><span class="o">(</span><span class="n">shape</span><span class="o">)*</span><span class="mi">2</span><span class="o">)</span>
<span class="n">scala</span><span class="o">></span> <span class="k">val</span> <span class="n">a</span> <span class="k">=</span> <span class="nc">NDArray</span><span class="o">.</span><span class="n">zeros</span><span class="o">(</span><span class="n">shape</span><span class="o">)</span>
<span class="n">scala</span><span class="o">></span> <span class="n">kv</span><span class="o">.</span><span class="n">pull</span><span class="o">(</span><span class="mi">3</span><span class="o">,</span> <span class="n">out</span> <span class="k">=</span> <span class="n">a</span><span class="o">)</span>
<span class="n">scala</span><span class="o">></span> <span class="n">a</span><span class="o">.</span><span class="n">toArray</span>
<span class="nc">Array</span><span class="o">[</span><span class="kt">Float</span><span class="o">]</span> <span class="k">=</span> <span class="nc">Array</span><span class="o">(</span><span class="mf">2.0</span><span class="o">,</span> <span class="mf">2.0</span><span class="o">,</span> <span class="mf">2.0</span><span class="o">,</span> <span class="mf">2.0</span><span class="o">,</span> <span class="mf">2.0</span><span class="o">,</span> <span class="mf">2.0</span><span class="o">)</span>
</pre></div>
</div>
</div>
<div class="section" id="push-aggregation-and-updater">
<span id="push-aggregation-and-updater"></span><h3>Push, Aggregation, and Updater<a class="headerlink" href="#push-aggregation-and-updater" title="Permalink to this headline"></a></h3>
<p>For any key that’s been initialized, you can push a new value with the same shape to the key, as follows:</p>
<div class="highlight-scala"><div class="highlight"><pre><span></span> <span class="n">scala</span><span class="o">></span> <span class="n">kv</span><span class="o">.</span><span class="n">push</span><span class="o">(</span><span class="mi">3</span><span class="o">,</span> <span class="nc">NDArray</span><span class="o">.</span><span class="n">ones</span><span class="o">(</span><span class="n">shape</span><span class="o">)*</span><span class="mi">8</span><span class="o">)</span>
<span class="n">scala</span><span class="o">></span> <span class="n">kv</span><span class="o">.</span><span class="n">pull</span><span class="o">(</span><span class="mi">3</span><span class="o">,</span> <span class="n">out</span> <span class="k">=</span> <span class="n">a</span><span class="o">)</span> <span class="c1">// pull out the value</span>
<span class="n">scala</span><span class="o">></span> <span class="n">a</span><span class="o">.</span><span class="n">toArray</span>
<span class="nc">Array</span><span class="o">[</span><span class="kt">Float</span><span class="o">]</span> <span class="k">=</span> <span class="nc">Array</span><span class="o">(</span><span class="mf">8.0</span><span class="o">,</span> <span class="mf">8.0</span><span class="o">,</span> <span class="mf">8.0</span><span class="o">,</span> <span class="mf">8.0</span><span class="o">,</span> <span class="mf">8.0</span><span class="o">,</span> <span class="mf">8.0</span><span class="o">)</span>
</pre></div>
</div>
<p>The data that you want to push can be stored on any device. Furthermore, you can push multiple
values into the same key, where KVStore first sums all of these
values, and then pushes the aggregated value, as follows:</p>
<div class="highlight-scala"><div class="highlight"><pre><span></span> <span class="n">scala</span><span class="o">></span> <span class="k">val</span> <span class="n">gpus</span> <span class="k">=</span> <span class="nc">Array</span><span class="o">(</span><span class="nc">Context</span><span class="o">.</span><span class="n">gpu</span><span class="o">(</span><span class="mi">0</span><span class="o">),</span> <span class="nc">Context</span><span class="o">.</span><span class="n">gpu</span><span class="o">(</span><span class="mi">1</span><span class="o">),</span> <span class="nc">Context</span><span class="o">.</span><span class="n">gpu</span><span class="o">(</span><span class="mi">2</span><span class="o">),</span> <span class="nc">Context</span><span class="o">.</span><span class="n">gpu</span><span class="o">(</span><span class="mi">3</span><span class="o">))</span>
<span class="n">scala</span><span class="o">></span> <span class="k">val</span> <span class="n">b</span> <span class="k">=</span> <span class="nc">Array</span><span class="o">(</span><span class="nc">NDArray</span><span class="o">.</span><span class="n">ones</span><span class="o">(</span><span class="n">shape</span><span class="o">,</span> <span class="n">gpus</span><span class="o">(</span><span class="mi">0</span><span class="o">)),</span> <span class="nc">NDArray</span><span class="o">.</span><span class="n">ones</span><span class="o">(</span><span class="n">shape</span><span class="o">,</span> <span class="n">gpus</span><span class="o">(</span><span class="mi">1</span><span class="o">)),</span> <span class="o">\</span>
<span class="n">scala</span><span class="o">></span> <span class="nc">NDArray</span><span class="o">.</span><span class="n">ones</span><span class="o">(</span><span class="n">shape</span><span class="o">,</span> <span class="n">gpus</span><span class="o">(</span><span class="mi">2</span><span class="o">)),</span> <span class="nc">NDArray</span><span class="o">.</span><span class="n">ones</span><span class="o">(</span><span class="n">shape</span><span class="o">,</span> <span class="n">gpus</span><span class="o">(</span><span class="mi">3</span><span class="o">)))</span>
<span class="n">scala</span><span class="o">></span> <span class="n">kv</span><span class="o">.</span><span class="n">push</span><span class="o">(</span><span class="mi">3</span><span class="o">,</span> <span class="n">b</span><span class="o">)</span>
<span class="n">scala</span><span class="o">></span> <span class="n">kv</span><span class="o">.</span><span class="n">pull</span><span class="o">(</span><span class="mi">3</span><span class="o">,</span> <span class="n">out</span> <span class="k">=</span> <span class="n">a</span><span class="o">)</span>
<span class="n">scala</span><span class="o">></span> <span class="n">a</span><span class="o">.</span><span class="n">toArray</span>
<span class="nc">Array</span><span class="o">[</span><span class="kt">Float</span><span class="o">]</span> <span class="k">=</span> <span class="nc">Array</span><span class="o">(</span><span class="mf">4.0</span><span class="o">,</span> <span class="mf">4.0</span><span class="o">,</span> <span class="mf">4.0</span><span class="o">,</span> <span class="mf">4.0</span><span class="o">,</span> <span class="mf">4.0</span><span class="o">,</span> <span class="mf">4.0</span><span class="o">)</span>
</pre></div>
</div>
<p>For each push command, KVStore applies the pushed value to the value stored by 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-scala"><div class="highlight"><pre><span></span> <span class="n">scala</span><span class="o">></span> <span class="k">val</span> <span class="n">updater</span> <span class="k">=</span> <span class="k">new</span> <span class="nc">MXKVStoreUpdater</span> <span class="o">{</span>
<span class="k">override</span> <span class="k">def</span> <span class="n">update</span><span class="o">(</span><span class="n">key</span><span class="k">:</span> <span class="kt">Int</span><span class="o">,</span> <span class="n">input</span><span class="k">:</span> <span class="kt">NDArray</span><span class="o">,</span> <span class="n">stored</span><span class="k">:</span> <span class="kt">NDArray</span><span class="o">)</span><span class="k">:</span> <span class="kt">Unit</span> <span class="o">=</span> <span class="o">{</span>
<span class="n">println</span><span class="o">(</span><span class="s">s"update on key </span><span class="si">$key</span><span class="s">"</span><span class="o">)</span>
<span class="n">stored</span> <span class="o">+=</span> <span class="n">input</span> <span class="o">*</span> <span class="mi">2</span>
<span class="o">}</span>
<span class="k">override</span> <span class="k">def</span> <span class="n">dispose</span><span class="o">()</span><span class="k">:</span> <span class="kt">Unit</span> <span class="o">=</span> <span class="o">{}</span>
<span class="o">}</span>
<span class="n">scala</span><span class="o">></span> <span class="n">kv</span><span class="o">.</span><span class="n">setUpdater</span><span class="o">(</span><span class="n">updater</span><span class="o">)</span>
<span class="n">scala</span><span class="o">></span> <span class="n">kv</span><span class="o">.</span><span class="n">pull</span><span class="o">(</span><span class="mi">3</span><span class="o">,</span> <span class="n">a</span><span class="o">)</span>
<span class="n">scala</span><span class="o">></span> <span class="n">a</span><span class="o">.</span><span class="n">toArray</span>
<span class="nc">Array</span><span class="o">[</span><span class="kt">Float</span><span class="o">]</span> <span class="k">=</span> <span class="nc">Array</span><span class="o">(</span><span class="mf">4.0</span><span class="o">,</span> <span class="mf">4.0</span><span class="o">,</span> <span class="mf">4.0</span><span class="o">,</span> <span class="mf">4.0</span><span class="o">,</span> <span class="mf">4.0</span><span class="o">,</span> <span class="mf">4.0</span><span class="o">)</span>
<span class="n">scala</span><span class="o">></span> <span class="n">kv</span><span class="o">.</span><span class="n">push</span><span class="o">(</span><span class="mi">3</span><span class="o">,</span> <span class="nc">NDArray</span><span class="o">.</span><span class="n">ones</span><span class="o">(</span><span class="n">shape</span><span class="o">))</span>
<span class="n">update</span> <span class="n">on</span> <span class="n">key</span> <span class="mi">3</span>
<span class="n">scala</span><span class="o">></span> <span class="n">kv</span><span class="o">.</span><span class="n">pull</span><span class="o">(</span><span class="mi">3</span><span class="o">,</span> <span class="n">a</span><span class="o">)</span>
<span class="n">scala</span><span class="o">></span> <span class="n">a</span><span class="o">.</span><span class="n">toArray</span>
<span class="nc">Array</span><span class="o">[</span><span class="kt">Float</span><span class="o">]</span> <span class="k">=</span> <span class="nc">Array</span><span class="o">(</span><span class="mf">6.0</span><span class="o">,</span> <span class="mf">6.0</span><span class="o">,</span> <span class="mf">6.0</span><span class="o">,</span> <span class="mf">6.0</span><span class="o">,</span> <span class="mf">6.0</span><span class="o">,</span> <span class="mf">6.0</span><span class="o">)</span>
</pre></div>
</div>
</div>
<div class="section" id="pull">
<span id="pull"></span><h3>Pull<a class="headerlink" href="#pull" title="Permalink to this headline"></a></h3>
<p>You’ve already seen how to pull a single key-value pair. Similar to the way that you use the push command, you can
pull the value into several devices with a single call.</p>
<div class="highlight-scala"><div class="highlight"><pre><span></span> <span class="n">scala</span><span class="o">></span> <span class="k">val</span> <span class="n">b</span> <span class="k">=</span> <span class="nc">Array</span><span class="o">(</span><span class="nc">NDArray</span><span class="o">.</span><span class="n">ones</span><span class="o">(</span><span class="n">shape</span><span class="o">,</span> <span class="n">gpus</span><span class="o">(</span><span class="mi">0</span><span class="o">)),</span> <span class="nc">NDArray</span><span class="o">.</span><span class="n">ones</span><span class="o">(</span><span class="n">shape</span><span class="o">,</span> <span class="n">gpus</span><span class="o">(</span><span class="mi">1</span><span class="o">)),\</span>
<span class="n">scala</span><span class="o">></span> <span class="nc">NDArray</span><span class="o">.</span><span class="n">ones</span><span class="o">(</span><span class="n">shape</span><span class="o">,</span> <span class="n">gpus</span><span class="o">(</span><span class="mi">2</span><span class="o">)),</span> <span class="nc">NDArray</span><span class="o">.</span><span class="n">ones</span><span class="o">(</span><span class="n">shape</span><span class="o">,</span> <span class="n">gpus</span><span class="o">(</span><span class="mi">3</span><span class="o">)))</span>
<span class="n">scala</span><span class="o">></span> <span class="n">kv</span><span class="o">.</span><span class="n">pull</span><span class="o">(</span><span class="mi">3</span><span class="o">,</span> <span class="n">outs</span> <span class="k">=</span> <span class="n">b</span><span class="o">)</span>
<span class="n">scala</span><span class="o">></span> <span class="n">b</span><span class="o">(</span><span class="mi">1</span><span class="o">).</span><span class="n">toArray</span>
<span class="nc">Array</span><span class="o">[</span><span class="kt">Float</span><span class="o">]</span> <span class="k">=</span> <span class="nc">Array</span><span class="o">(</span><span class="mf">6.0</span><span class="o">,</span> <span class="mf">6.0</span><span class="o">,</span> <span class="mf">6.0</span><span class="o">,</span> <span class="mf">6.0</span><span class="o">,</span> <span class="mf">6.0</span><span class="o">,</span> <span class="mf">6.0</span><span class="o">)</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="list-key-value-pairs">
<span id="list-key-value-pairs"></span><h2>List Key-Value Pairs<a class="headerlink" href="#list-key-value-pairs" title="Permalink to this headline"></a></h2>
<p>All of the operations that we’ve discussed so far are performed on a single key. KVStore also provides
the interface for generating a list of key-value pairs. For a single device, use the following:</p>
<div class="highlight-scala"><div class="highlight"><pre><span></span> scala> val keys = Array(5, 7, 9)
scala> kv.init(keys, Array.fill(keys.length)(NDArray.ones(shape)))
scala> kv.push(keys, Array.fill(keys.length)(NDArray.ones(shape)))
update on key: 5
update on key: 7
update on key: 9
scala> val b = Array.fill(keys.length)(NDArray.zeros(shape))
scala> kv.pull(keys, outs = b)
scala> b(1).toArray
Array[Float] = Array(3.0, 3.0, 3.0, 3.0, 3.0, 3.0)
</pre></div>
</div>
</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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<ul>
<li class="toctree-l1"><a class="reference external" href="https://mxnet.incubator.apache.org/tutorials/index.html#Python-Tutorials">Scala Tutorials</a></li>
</ul>
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<h3><a href="../../index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">KVStore API</a><ul>
<li><a class="reference internal" href="#basic-push-and-pull">Basic Push and Pull</a><ul>
<li><a class="reference internal" href="#initialization">Initialization</a></li>
<li><a class="reference internal" href="#push-aggregation-and-updater">Push, Aggregation, and Updater</a></li>
<li><a class="reference internal" href="#pull">Pull</a></li>
</ul>
</li>
<li><a class="reference internal" href="#list-key-value-pairs">List Key-Value Pairs</a></li>
<li><a class="reference internal" href="#next-steps">Next Steps</a></li>
</ul>
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