The work_mem variable does not only speed up grouping. It can also have a very nice impact on simple things such as sorting, which is an essential mechanism mastered by every database system in the world.
The following query shows a simple operation using the default setting of 4 MB:
test=# SET work_mem TO default; SET test=# EXPLAIN ANALYZE SELECT * FROM t_test ORDER BY name, id; QUERY PLAN ----------------------------------------------------------------- Sort (cost=24111.14..24611.14 rows=200000 width=9) (actual time=219.298..235.008 rows=200000 loops=1) Sort Key: name, id Sort Method: external sort Disk: 3712kB -> Seq Scan on t_test (cost=0.00..3082.00 rows=200000 width=9) (actual time=0.006..13.807 rows=200000 ...
