2014-08-28 12:08 GMT+03:00 gmb <gmbouwer@xxxxxxxxx>:
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 ;
I think index will be of no help here, as (1) you're reading whole table anyway and (2) `amount` is not part of your index.
Try to avoid disk-based sort by increasing `work_mem` for your session, I think value in the range 120MB-150MB should work:
SET work_mem TO '150MB';
Check `EXPLAIN` output after the change.
Victor Y. Yegorov