title: Magento - “Manage Categories” Stop working when there are too many products under a certain category
body: <p>I have this issue in Magento and wish someone here can help.</p>
  
  <p>In my store, there is a category has more than 3000 products. I upload an image to this category to make it as the feature image. I click on the “Save Category” and the"Please wait...” shows up but the page just hangs at this stage forever.</p>
  
  <p>I checked the firebug console and found actually there was no AJAX return, so I guess the system did not response properly. But when I create a new category with 800 products, and upload an feature image and save, it took 6 seconds to get the AJAX back. </p>
  
  <p>I have also set the PHP memory_limit to 512M and the PHP max_execution_time is 18000s, but no help.</p>
  
  <p>I also tried to find the solution online but not clue.</p>
  
  <p>PS: This problem also happens when I try to reorder categories which have too many products (say 5000 products).</p>