Thread: optimizing number of workers

server, I'm trying to do some reasonable efforts to configure it correctly. The hard

ware has 128 cores, and I am running a VM with Redhat 9 and Postgresql  16.9.

In postgresql.conf I have:

max_worker_processes = 90               # (change requires restart)
max_parallel_workers_per_gather = 72    # gsh 26 oct 2022
max_parallel_maintenance_workers = 72   # gsh 12 jun 2025
max_parallel_workers =  72              # gsh 12 jun 2025
max_logical_replication_workers = 72    # gsh 12 jun 2025
max_sync_workers_per_subscription = 72   # gsh 12 jun 2025
autovacuum_max_workers = 12             # max number of autovacuum subprocesses

When I do a simple count of a large (large being 1.8 Billion entries), I get

about 10 workers used.

prod_v1_0_0_rc1=# explain (analyze, buffers) select count(*) from gaiadr3.gaia_source;
                                                                                         QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Finalize Aggregate  (cost=14379796.81..14379796.82 rows=1 width=8) (actual time=16702.806..16705.479 rows=1 loops=1)
   Buffers: shared hit=2507481
   ->  Gather  (cost=14379795.78..14379796.79 rows=10 width=8) (actual time=16702.513..16705.470 rows=11 loops=1)
         Workers Planned: 10
         Workers Launched: 10
         Buffers: shared hit=2507481
         ->  Partial Aggregate  (cost=14379785.78..14379785.79 rows=1 width=8) (actual time=16691.820..16691.821 rows=1 loops=11)
               Buffers: shared hit=2507481
               ->  Parallel Index Only Scan using gaia_source_nest128 on gaia_source  (cost=0.58..13926632.85 rows=181261171 width=0) (actual time=0.025..9559.644 rows=164700888 loops=11)
                     Heap Fetches: 0
                     Buffers: shared hit=2507481
 Planning:
   Buffers: shared hit=163
 Planning Time: 14.898 ms
 Execution Time: 16705.592 ms

Postgres has chosen to use only a small fraction of the CPU's I have on

my machine. Given the query returns an answer in about 8 seconds, it may be

that Postgresql has allocated the proper number of works. But if I wanted

to try to tweak some config parameters to see if using more workers

would give me an answer faster, I don't seem to see any obvious knobs

to turn. Are there parameters that I can adjust to see if I can increase

throughput? Would adjusting parallel_setup_cost or parallel_tuple_cost

likely to be of help?