title: APACHE POI autoSizeColumn with useMergedCells too slow
body: <p>I try to apply autoSizeColumn on an Excel sheet. I'm using POI 3.10.1.<br>
  I apply autoSizeColumn at the end but the problem is than the process is too slow/long anyway: 
  On the sheet I've approximately 1000 lines and 20 columns... After 5 hours, I kill the process ...<br>
  I don't understand what is taking so long, 1000 lines and 20 columns doesn't appear so huge: Did I miss something? (nb: on a smaller file, it's working)<br>
  My simplified code below:</p>
  
  <pre><code>    Workbook vWorkbook = getWorkbook();
  
      Sheet vSheet = vWorkbook.createSheet("sheet");
      CreationHelper vHelper = vWorkbook.getCreationHelper();
      Drawing drawing = vSheet.createDrawingPatriarch();
  
      Set&lt;CellRangeAddress&gt; vRegions = new HashSet&lt;CellRangeAddress&gt;();
  
      //Parcours des lignes du document
      MatrixDocument vMatrixDocument = getMatrixDocument();
      List&lt;MatrixRow&gt; vListMatrixRows = vMatrixDocument.getRows();
      int maxColNb = 0;
  
      //Parcours des lignes de la grille.
      for (MatrixRow vMatrixRow : vListMatrixRows)
      {
          //(...)
          //create cells 
          //(...)
      }
  
      initColSpan(vListMatrixRows, vRegions);
  
      //Gestion des colSpan et des RowSpan
      for (CellRangeAddress vRegion : vRegions)
      {
          vSheet.addMergedRegion(vRegion);
      }
  
      for (int i = 0; i &lt; maxColNb; ++i)
      {
          vSheet.autoSizeColumn(i, true);//Here the problem. spent more than 5 hour for 1000 lines and 20 columns
      }
  </code></pre>
  
  <p>I've already read threads below : </p>
  
  <ul>http://stackoverflow.com/questions/16943493/apache-poi-autosizecolumn-resizes-incorrectly</ul>
  
  <ul>http://stackoverflow.com/questions/15740100/apache-poi-autosizecolumn-not-working-right</ul>
  
  <ul>http://stackoverflow.com/questions/23366606/autosizecolumn-performance-effect-in-apache-poi</ul>
  
  <ul>http://stackoverflow.com/questions/18984785/a-poi-related-code-block-running-dead-slow</ul>
  
  <ul>http://stackoverflow.com/questions/28564045/apache-poi-autosizecolumn-behaving-weird</ul>
  
  <ul>http://stackoverflow.com/questions/18456474/apache-poi-autosizecolumn-is-not-working</ul>
  
  <p>But none solve my issue.<br>
  Any idea ?
  PS : I tried to upload an example image of the Excel file but I don't find how to upload it.</p>