PlanetNTF

There is a large problem with data context variables if they are bound dynamically.
They will be recomputed again and again, even when in Partial Execution mode and if they are not in use. Here is a small demo XPage:

<?xml version="1.0" encoding="UTF-8"?>
<xp:view xmlns:xp="http://www.ibm.com/xsp/core">

   <xp:this.dataContexts>
      <xp:dataContext var="dataContext">
         <xp:this.value>
            <![CDATA[#{javascript:
               // Sleep for 100ms
               java.lang.Thread.currentThread().sleep( 100 );
               print('-=> Recalc: ' + java.lang.System.currentTimeMillis());
               return true;
            }]]>
          </xp:this.value>
       </xp:dataContext>
    </xp:this.dataContexts>

   <xp:label id="labelRefreshMe">
      <xp:this.value>
         <![CDATA[#{javascript:
            java.lang.System.currentTimeMillis()
         }]]>
      </xp:this.value>
   </xp:label>

   <xp:button value="Refresh" id="buttonRefresh" >
      <xp:eventHandler event="onclick" submit="false"
         refreshMode="partial"
         refreshId="labelRefreshMe"
         execId="labelRefreshMe"
         execMode="partial" />
   </xp:button>

</xp:view>

If you are open the XPage, a dataContext variable will be recalculated for three times:

Clicking on the button will recalculate them up to eleven times:

Keep in mind: Partial Refresh & Partial Execution is enabled. That makes them only useable if their values are computed on page load.