Parameter and Command Reference > Connector Framework Server Parameters > Indexing Parameters > KillDuplicates 

Use this parameter to specify the string that gets used as the KillDuplicates parameter value when sending an index command to IDOL server.
The following options are available for this parameter:
REFERENCE - Replaces an existing document with the new document if the document to index has the same value in its DREREFERENCE field.
The default is to leave the value blank, in which case nothing is appended to the command sent to IDOL. This allows duplicate documents in IDOL server - IDOL server does not replace nor delete documents.
For more information, refer to the IDOL Server Administration Guide.