Reduce execution time of my query in postgresql - postgresql

Question

Below is my query. It takes 9387.430 ms to execute, which is certainly too long for such a request. I would like to be able to reduce this execution time. Can you please help me on this ? I also provided my analyze output.
EXPLAIN ANALYZE
SELECT a.artist, b.artist, COUNT(*)
FROM release_has_artist a, release_has_artist b
WHERE a.release = b.release AND a.artist <> b.artist
GROUP BY(a.artist,b.artist)
ORDER BY (a.artist,b.artist);;
Output of EXPLAIN ANALYZE :
Sort (cost=1696482.86..1707588.14 rows=4442112 width=48) (actual time=9253.474..9314.510 rows=461386 loops=1)
Sort Key: (ROW(a.artist, b.artist))
Sort Method: external sort Disk: 24832kB
-> Finalize GroupAggregate (cost=396240.32..932717.19 rows=4442112 width=48) (actual time=1928.058..2911.463 rows=461386 loops=1)
Group Key: a.artist, b.artist
-> Gather Merge (cost=396240.32..860532.87 rows=3701760 width=16) (actual time=1928.049..2494.638 rows=566468 loops=1)
Workers Planned: 2
Workers Launched: 2
-> Partial GroupAggregate (cost=395240.29..432257.89 rows=1850880 width=16) (actual time=1912.809..2156.951 rows=188823 loops=3)
Group Key: a.artist, b.artist
-> Sort (cost=395240.29..399867.49 rows=1850880 width=8) (actual time=1912.794..2003.776 rows=271327 loops=3)
Sort Key: a.artist, b.artist
Sort Method: external merge Disk: 4848kB
-> Merge Join (cost=0.85..177260.72 rows=1850880 width=8) (actual time=2.143..1623.628 rows=271327 loops=3)
Merge Cond: (a.release = b.release)
Join Filter: (a.artist <> b.artist)
Rows Removed by Join Filter: 687597
-> Parallel Index Only Scan using release_has_artist_pkey on release_has_artist a (cost=0.43..67329.73 rows=859497 width=8) (actual time=0.059..240.998 rows=687597 loops=3)
Heap Fetches: 711154
-> Index Only Scan using release_has_artist_pkey on release_has_artist b (cost=0.43..79362.68 rows=2062792 width=8) (actual time=0.072..798.402 rows=2329742 loops=3)
Heap Fetches: 2335683
Planning time: 2.101 ms
Execution time: 9387.430 ms

Answer 1

In your EXPLAIN ANALYZE output, there are two Sort Method: external merge Disk: ####kB, indicating that the sort spilled out to disk and not in memory, due to an insufficiently-sized work_mem. Try increasing your work_mem up to 32MB (30 might be ok, but I like multiples of 8), and try again
Note that you can set work_mem on a per-session basis, as a global change in work_mem could potentially have negative side-effects, such as running out of memory, because postgresql.conf-configured work_mem is allocated for each session (basically, it has a multiplicative effect).