title: How to combine multiple PCollections together and give it as input to a ParDo function
body: <p>I have some six PCollections as KV. I want to do ParDo on another PCollection by giving the combined (6) PCollections as sideInput. </p>
  
  <p>I tried giving all 6 PCollections as separate sideInput as below</p>
  
  <pre><code>PCollection&lt;TableRow&gt; OutputRows = MyCollection.apply(ParDo.withSideInputs(Inp1, Inp2,...)
      .of(new DoFn&lt;KV&lt;String, String&gt;, TableRow&gt;() {
          ...
      }
  </code></pre>
  
  <p>But its throwing OutOfMemoryError as the heap space exceeds. Please advice on how to combine the PCollections to give as input to another PCollection. </p>