Re: Performance issue: index not used on GROUP BY...

GroupAggregate  (cost=303425.31..339014.43 rows=136882 width=48) (actual
time=4708.181..6688.699 rows=287268 loops=1)
  Buffers: shared read=23899, temp read=30974 written=30974
  ->  Sort  (cost=303425.31..306847.34 rows=1368812 width=48) (actual
time=4708.170..5319.429 rows=1368744 loops=1)
        Sort Key: co_id, client_id, doc_no,
        Sort Method: external merge  Disk: 80304kB
        Buffers: shared read=23899, temp read=30974 written=30974
        ->  Seq Scan on ddetail  (cost=0.00..37587.12 rows=1368812 width=48)
(actual time=0.122..492.964 rows=1368744 loops=1)
              Buffers: shared read=23899
Total runtime: 6708.244 ms


My initial attempt was this  (this is what I actually need):

SELECT  co_id ,  client_id , doc_no ,  line_id , batch_no , sum( amount  )
FROM ddetail
GROUP BY co_id ,  client_id , doc_no ,  line_id  , batch_no ;