title: Which situation is it better to use coalesce vs repartition
body: <p>I have data that is partitioned as statically partitioned by data and dynamically partitioned by country. So for each date, I could have as much as 180 country partitions. Looks something like this:</p>
  
  <pre><code>/20180101/cntry=us/ =&gt; 100kb
           /cntry=ca/ =&gt; 500kb
           /cntry=uk/ =&gt; 1.5mb
  </code></pre>
  
  <p>For each date, the data is small (around 20-100mb) and it is divided among the country partitions. I was wondering for a situation like this, which method would be better? Repartition or coalesce? Since the data is small, would coalesce be better? I am very confused as to when coalesce or repartition would be a better choice depending on the size of the data.</p>