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Apache Aries - Using the Coordinator to optimise Transactions
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<h1 id="using-the-coordinator-to-optimise-transactions">Using the Coordinator to optimise Transactions<a class="headerlink" href="#using-the-coordinator-to-optimise-transactions" title="Permanent link">&para;</a></h1>
<p>The transaction control service provides a transactional scope around resource access, but sometimes it
makes sense to delay doing this work until it can be batched efficiently together in a single transaction:</p>
<h2 id="bulk-resource-access">Bulk resource access<a class="headerlink" href="#bulk-resource-access" title="Permanent link">&para;</a></h2>
<p>In this case we simply do each insert in a separate transaction:</p>
<div class="codehilite"><pre><span class="n">public</span> <span class="n">void</span> <span class="n">persistMessage</span><span class="p">(</span><span class="n">String</span> <span class="n">message</span><span class="p">)</span> <span class="p">{</span>
<span class="n">txControl</span><span class="p">.</span><span class="n">required</span><span class="p">(()</span> <span class="o">-&gt;</span> <span class="p">{</span>
<span class="n">PreparedStatement</span> <span class="n">ps</span> <span class="p">=</span> <span class="n">connection</span><span class="p">.</span><span class="n">prepareStatement</span><span class="p">(</span>
&quot;<span class="n">Insert</span> <span class="n">into</span> <span class="n">TEST_TABLE</span> <span class="n">values</span> <span class="p">(</span> ? <span class="p">)</span>&quot;<span class="p">);</span>
<span class="n">ps</span><span class="p">.</span><span class="n">setString</span><span class="p">(</span>1<span class="p">,</span> <span class="n">message</span><span class="p">);</span>
<span class="k">return</span> <span class="n">ps</span><span class="p">.</span><span class="n">executeUpdate</span><span class="p">();</span>
<span class="p">});</span>
<span class="p">}</span>
</pre></div>
<p>If called a large number of times from an external service:</p>
<div class="codehilite"><pre><span class="n">List</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span> <span class="n">messages</span> <span class="p">=</span> <span class="n">getMessages</span><span class="p">();</span>
<span class="n">messages</span><span class="p">.</span><span class="n">stream</span><span class="p">()</span>
<span class="p">.</span><span class="n">forEach</span><span class="p">(</span><span class="n">svc</span><span class="p">::</span><span class="n">persistMessage</span><span class="p">);</span>
</pre></div>
<p>Then this code can be quite slow as the message list becomes large</p>
<h2 id="the-naive-approach">The naive approach<a class="headerlink" href="#the-naive-approach" title="Permanent link">&para;</a></h2>
<p>The obvious way to reduce overhead is to batch all of the inserts into a single transaction:</p>
<div class="codehilite"><pre><span class="n">List</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span> <span class="n">messages</span> <span class="p">=</span> <span class="n">getMessages</span><span class="p">();</span>
<span class="n">txControl</span><span class="p">.</span><span class="n">required</span><span class="p">(()</span> <span class="o">-&gt;</span> <span class="p">{</span>
<span class="n">messages</span><span class="p">.</span><span class="n">stream</span><span class="p">()</span>
<span class="p">.</span><span class="n">forEach</span><span class="p">(</span><span class="n">svc</span><span class="p">::</span><span class="n">persistMessage</span><span class="p">);</span>
<span class="k">return</span> <span class="n">null</span><span class="p">;</span>
<span class="p">});</span>
</pre></div>
<p>This reuses the same physical connection each time, and it avoids repeated commits, so it should be faster
right?</p>
<p>Actually it turns out that this approach can be slower for some databases. By building up a very large
transaction it can actually slow down the rate at which data can be insterted.</p>
<h2 id="using-the-coordinator">Using the coordinator<a class="headerlink" href="#using-the-coordinator" title="Permanent link">&para;</a></h2>
<p>By adding in the Coordinator we can <strong>dramatically</strong> improve our performance:</p>
<div class="codehilite"><pre><span class="n">public</span> <span class="n">void</span> <span class="n">persistMessage</span><span class="p">(</span><span class="n">String</span> <span class="n">message</span><span class="p">)</span> <span class="p">{</span>
<span class="k">if</span><span class="p">(</span><span class="n">coordinator</span><span class="p">.</span><span class="n">addParticipant</span><span class="p">(</span><span class="n">this</span><span class="p">))</span> <span class="p">{</span>
<span class="p">((</span><span class="n">List</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span><span class="p">)</span><span class="n">coordinator</span><span class="p">.</span><span class="n">peek</span><span class="p">().</span><span class="n">getVariables</span><span class="p">()</span>
<span class="p">.</span><span class="n">computeIfAbsent</span><span class="p">(</span><span class="n">getClass</span><span class="p">(),</span> <span class="n">k</span> <span class="o">-&gt;</span> <span class="n">new</span> <span class="n">ArrayList</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span><span class="p">()))</span>
<span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">message</span><span class="p">);</span>
<span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
<span class="n">txControl</span><span class="p">.</span><span class="n">required</span><span class="p">(()</span> <span class="o">-&gt;</span> <span class="p">{</span>
<span class="n">PreparedStatement</span> <span class="n">ps</span> <span class="p">=</span> <span class="n">connection</span><span class="p">.</span><span class="n">prepareStatement</span><span class="p">(</span>
&quot;<span class="n">Insert</span> <span class="n">into</span> <span class="n">TEST_TABLE</span> <span class="n">values</span> <span class="p">(</span> ? <span class="p">)</span>&quot;<span class="p">);</span>
<span class="n">ps</span><span class="p">.</span><span class="n">setString</span><span class="p">(</span>1<span class="p">,</span> <span class="n">message</span><span class="p">);</span>
<span class="k">return</span> <span class="n">ps</span><span class="p">.</span><span class="n">executeUpdate</span><span class="p">();</span>
<span class="p">});</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">@</span><span class="n">Override</span>
<span class="n">public</span> <span class="n">void</span> <span class="n">ended</span><span class="p">(</span><span class="n">Coordination</span> <span class="n">coord</span><span class="p">)</span> <span class="n">throws</span> <span class="n">Exception</span> <span class="p">{</span>
<span class="n">txControl</span><span class="p">.</span><span class="n">required</span><span class="p">(()</span> <span class="o">-&gt;</span> <span class="p">{</span>
<span class="n">List</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span> <span class="n">l</span> <span class="p">=</span> <span class="p">(</span><span class="n">List</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span><span class="p">)</span> <span class="n">coord</span><span class="p">.</span><span class="n">getVariables</span><span class="p">()</span>
<span class="p">.</span><span class="n">get</span><span class="p">(</span><span class="n">getClass</span><span class="p">());</span>
<span class="n">PreparedStatement</span> <span class="n">ps</span> <span class="p">=</span> <span class="n">connection</span><span class="p">.</span><span class="n">prepareStatement</span><span class="p">(</span>
&quot;<span class="n">Insert</span> <span class="n">into</span> <span class="n">TEST_TABLE</span> <span class="n">values</span> <span class="p">(</span> ? <span class="p">)</span>&quot;<span class="p">);</span>
<span class="n">l</span><span class="p">.</span><span class="n">stream</span><span class="p">().</span><span class="n">forEach</span><span class="p">(</span><span class="n">s</span> <span class="o">-&gt;</span> <span class="p">{</span>
<span class="k">try</span> <span class="p">{</span>
<span class="n">ps</span><span class="p">.</span><span class="n">setString</span><span class="p">(</span>1<span class="p">,</span> <span class="n">s</span><span class="p">);</span>
<span class="n">ps</span><span class="p">.</span><span class="n">addBatch</span><span class="p">();</span>
<span class="p">}</span> <span class="k">catch</span> <span class="p">(</span><span class="n">SQLException</span> <span class="n">sqle</span><span class="p">)</span> <span class="p">{</span>
<span class="n">throw</span> <span class="n">new</span> <span class="n">RuntimeException</span><span class="p">(</span><span class="n">sqle</span><span class="p">);</span>
<span class="p">}</span>
<span class="p">});</span>
<span class="k">return</span> <span class="n">ps</span><span class="p">.</span><span class="n">executeBatch</span><span class="p">();</span>
<span class="p">});</span>
<span class="p">}</span>
</pre></div>
<p>Now, if we do our bulk add inside a coordination:</p>
<div class="codehilite"><pre><span class="n">coordinator</span><span class="p">.</span><span class="n">begin</span><span class="p">(</span>&quot;<span class="n">foo</span>&quot;<span class="p">,</span> <span class="n">MINUTES</span><span class="p">.</span><span class="n">toMillis</span><span class="p">(</span>5<span class="p">));</span>
<span class="k">try</span> <span class="p">{</span>
<span class="n">messages</span><span class="p">.</span><span class="n">stream</span><span class="p">()</span>
<span class="p">.</span><span class="n">forEach</span><span class="p">(</span><span class="n">this</span><span class="p">::</span><span class="n">persistMessage</span><span class="p">);</span>
<span class="p">}</span> <span class="n">finally</span> <span class="p">{</span>
<span class="n">coordinator</span><span class="p">.</span><span class="n">peek</span><span class="p">().</span><span class="k">end</span><span class="p">();</span>
<span class="p">}</span>
</pre></div>
<p>Then we find that it is <strong>much</strong> faster! This is because we can make use of more efficient JDBC API, and
because we can batch up a suitable number of inserts in a single transaction.</p></div>
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