Tom,
The query which you gave returns me 0 rows.
select ctid,xmin,xmax,* from pg_index where indexrelid in
          (select indexrelid from pg_index group by 1 having count(*)>1);
Regards,
Bhakti
On Sat, Feb 26, 2011 at 10:55 PM, Tom Lane 
<tgl@sss.pgh.pa.us> wrote:
Bhakti Ghatkar <
bghatkar@zedo.com> writes:
 > We were running full vacuum on DB when we encountered the error below;
> INFO:  vacuuming "pg_catalog.pg_index"
 > *vacuumdb: vacuuming of database "rpt_production" failed: ERROR:  duplicate
 > key value violates unique constraint "pg_index_indexrelid_index"*
 > DETAIL:  Key (indexrelid)=(2678) already exists.
That's pretty bizarre, but what makes you think it has anything to do
 with temp tables?  OID 2678 is pg_index_indexrelid_index itself.
 It looks to me like you must have duplicate rows in pg_index for that
 index (and maybe others?), and the problem is exposed during vacuum full
 because it tries to rebuild the indexes.
 Could we see the output of
        select ctid,xmin,xmax,* from pg_index where indexrelid in
          (select indexrelid from pg_index group by 1 having count(*)>1);
                        regards, tom lane