Bulkloading using COPY - ignore duplicates?

Hello,

I'm in the process of porting a large application from Ingres to
PostgreSQL. We make heavy use of bulkloading using the 'COPY'
statement in ESQL/C. Consider the SQL statements below (in a psql
session on an arbitrary database):

 CREATE TABLE copytest(f1 INTEGER, f2 INTEGER);
 CREATE UNIQUE INDEX copytest_idx ON copytest USING BTREE(f1, f2);
 COPY copytest FROM '/tmp/copytest';

Given the file /tmp/copytest:

 1	1
 2	2
 3	3
 4	4
 4	4
 5	5
 6	6

will result in the following output:

 ERROR:  copy: line 5, Cannot insert a duplicate key into unique index copytest_idx

However my application code is assuming that duplicate rows will
simply be ignored (this is the case in Ingres, and I believe Oracle's
bulkloader too). I propose modifying _bt_check_unique() in
/backend/access/nbtree/nbtinsert.c to emit a NOTICE (rather than
ERROR) elog() and return NULL (or appropriate) to the calling function
if a duplicate key is detected and a 'COPY FROM' is in progress (add
new parameter to flag this).

Would this seem a reasonable thing to do? Does anyone rely on COPY
FROM causing an ERROR on duplicate input? Would:

 WITH ON_DUPLICATE = CONTINUE|TERMINATE (or similar)

need to be added to the COPY command (I hope not)?

Thanks,

-- 
 Lee Kindness, Senior Software Engineer
 Concept Systems Limited.