- new GUC in "Statement Behaviour" section, notify_duplicate_removal
(default true)
Initial discussion in this thread:
http://www.postgresql.org/message-id/CAP_rwwmpzk9=SbjRZTOd05bDctyC43wNKnu_m37dYGvL4SAeSw@mail.gmail.com
Rationale: for some legitimate use cases, duplicate removal is not
required, and it gets O(N^2) cost on large COPY/ insert transactions.