=?ISO-8859-1?Q?Torsten_F=F6rtsch?= <torsten.foertsch@xxxxxxx> writes: > I have a query that involves an external sort: > -> Sort (cost=13662680.01..13850498.48 rows=75127389 width=16) > (actual time=980098.397..1021411.862 rows=74181544 loops=1) > Sort Key: (ROW(account_id, (purchase_time)::date)) > Sort Method: external merge Disk: 3118088kB > Buffers: shared hit=1568637 read=1327223, > temp read=389763 written=389763 > What puzzles me is that this happens even when I set work_mem to 50GB in > the session. > Why does it still use the external merge? Seems odd. I wouldn't have been surprised if you'd said it didn't do it at work_mem = 5GB. The internal memory requirement can be noticeably larger than the space required on-disk, mainly because we go to some lengths to minimize the size of sort tuples when writing them out, but not if they stay in memory. But a difference of more than maybe 2X to 3X from that effect would be surprising. Perhaps you fat-fingered the SET somehow? regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
