title: ActiveRecords select(:id).collect vs. pluck(:id) methods: Why is pure AR "pluck" slower?
body: <p>I am trying to get all the ids from my Article model. I can do it two ways:</p>
  
  <pre><code> Article.select(:id).collect{|a| a.id}
    Article Load (2.6ms)  SELECT "articles"."id" FROM "articles" 
  </code></pre>
  
  <p>OR</p>
  
  <pre><code>2.2.1 :006 &gt; Article.pluck(:id)
     (4.3ms)  SELECT "articles"."id" FROM "articles"
  </code></pre>
  
  <p>What gives? Why is the AR slower than the Ruby version?</p>
  
  <p>Even when I benchmark the Ruby method, it seems faster:</p>
  
  <pre><code>Benchmark.measure{Article.select(:id).collect{|a| a.id}}
    Article Load (1.9ms)  SELECT "articles"."id" FROM "articles"
   =&gt; #&lt;Benchmark::Tms:0x007feb12060658 @label="", @real=0.026455502957105637, @cstime=0.0, @cutime=0.0, @stime=0.0, @utime=0.020000000000000018, @total=0.020000000000000018&gt;
  </code></pre>