anchor.diff:  
   Expert: Non-leader nodes need to synchronize their update logs with their leader node from time to time in order to clean deprecated transaction log files. By default, such a synchronization process is performed every minute. The schedule of the synchronization can be modified with a “updateLogSynchronizer” list as follows:
   
  +TIP: If the updateLogSynchronizer element is omitted from the Source cluster, transaction logs may accumulate on non-leaders.
  +
   `schedule`::
    The delay in milliseconds for synchronizing the update logs. The default is `60000`.
   
   ==== The Buffer Element
   
  -When buffering updates, the update logs will store all the updates indefinitely. It is recommended to disable buffering on both the Source and Target clusters during normal operation as when buffering is enabled the Update Logs will grow without limit. Leaving buffering enabled is intended for special maintenance periods. The buffer can be disabled at startup with a “buffer” list and the parameter “defaultState” as follows:
  +When buffering updates, the update logs will store all the updates indefinitely. It is best to disable buffering on both the Source and Target clusters during normal operation as when buffering is enabled the Update Logs will grow without limit. Enbling buffering is intended for special maintenance periods. Buffering can be disabled at startup with a “buffer” list and the parameter “defaultState” as follows:
   
   `defaultState`::
   The state of the buffer at startup. The default is `enabled`.
  
positive.code: [source,xml]
  ----
  <requestHandler name="/cdcr" class="solr.CdcrRequestHandler">
    <lst name="buffer">
      <str name="defaultState">disabled</str>
    </lst>
  
negative.code: 
  === Source Configuration
  
  Here is a sample of a Source configuration file, a section in `solrconfig.xml`. The presence of the <replica> section causes CDCR to use this cluster as the Source and should not be present in the Target collections. Details about each setting are after the two examples. The source example has buffering disabled, the default is enabled:
  
  [source,xml]
  ----
  <updateRequestProcessorChain name="cdcr-processor-chain">
    <processor class="solr.CdcrUpdateProcessorFactory"/>
    <processor class="solr.RunUpdateProcessorFactory"/>
  </updateRequestProcessorChain>
  
  <requestHandler name="/update" class="solr.UpdateRequestHandler">
    <lst name="defaults">
      <str name="update.chain">cdcr-processor-chain</str>
    </lst>
  </requestHandler>
  
  <requestHandler name="/cdcr" class="solr.CdcrRequestHandler">
    <lst name="replica">
      <str name="zkHost">10.240.18.211:2181,10.240.18.212:2181</str>
  