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PORails & Memcached: Optimizing multiple fetches
 

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    <p>I am building a Rails backend to an iPhone app.</p> <p>After profiling my application, I have found the following call to be especially expensive in terms of performance:</p> <pre><code>@messages.as_json </code></pre> <p>This call returns about 30 message objects, each including many child records. As you can see, a single message json response may make many DB calls to be composed:</p> <pre><code> def as_json(options={}) super(:only =&gt; [...], :include =&gt; { :user =&gt; {...}, :checkin =&gt; {...} }}, :likes =&gt; {:only =&gt; [...], :include =&gt; { :user =&gt; {...] }}}, :comments =&gt; {:only =&gt; [...], :include =&gt; { :user =&gt; {:only =&gt; [...] }}} }, :methods =&gt; :top_highlight) end </code></pre> <p>On average the <code>@messages.as_json</code>call (all 30 objects) takes almost 1100ms.</p> <p>Wanting to optimize I've employed memcached. With the solution below, when all my message objects are in cache, average response is now 200-300ms. I'm happy with this, but the issue I have is that this has made cache miss scenarios even slower. In cases where nothing is in cache, it now takes over 2000ms to compute.</p> <pre><code> # Note: @messages has the 30 message objects in it, but none of the child records have been grabbed @messages.each_with_index do |m, i| @messages[i] = Rails.cache.fetch("message/#{m.id}/#{m.updated_at.to_i}") do m.as_json end end </code></pre> <p>I understand that there will have to be some overhead to check the cache for each object. But I'm guessing there is a more efficient way to do it than the way I am now, which is basically serially, one-by-one. Any pointers on making this more efficient?</p>
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