anchor.diff:  
   In the previous section, we saw that the `updateRequestProcessorChain` was configured with `processor="remove_blanks, signature"`. This means that such processors are of the #1 kind and are run only on the forwarding nodes. Similarly, we can configure them as the #2 kind by specifying with the attribute "post-processor" as follows:
   
  -.post-processors
  +.post-processor Configuration
   [source,xml]
   ----
   <updateProcessorChain name="custom" processor="signature" post-processor="remove_blanks">
  
positive.code: 
  In this case, an instance of `SignatureUpdateProcessorFactory` is configured with the name "signature" and a `RemoveBlankFieldUpdateProcessorFactory` is defined with the name "remove_blanks". Once the above has been specified in `solrconfig.xml`, we can be refer to them in update request processor chains in `solrconfig.xml` as follows:
  
  .updateRequestProcessorChains and updateProcessors
  [source,xml]
  ----
  <updateProcessorChain name="custom" processor="remove_blanks,signature">
  
negative.code: ----
  
  However executing a processor only on the forwarding nodes is a great way of distributing an expensive computation such as de-duplication across a SolrCloud cluster by sending requests randomly via a load balancer. Otherwise the expensive computation is repeated on both the leader and replica nodes.
  
  .Custom update chain post-processors may never be invoked on a recovering replica
  [WARNING]
  