WITH selected AS
    (SELECT username FROM profiles
        WHERE queued = false FOR UPDATE SKIP LOCKED LIMIT %(n)s)
UPDATE profiles
    SET
        queued = true
    WHERE username IN (SELECT username FROM selected)
RETURNING username;

INSERT INTO profiles (
    ...
) values (
    ...
)
ON CONFLICT (username) DO UPDATE
    SET
        ...
;

max_connections = 100
shared_buffers = 2560MB
effective_cache_size = 7680MB
maintenance_work_mem = 640MB
checkpoint_completion_target = 0.9
wal_buffers = 16MB
default_statistics_target = 100
random_page_cost = 1.1
effective_io_concurrency = 200
work_mem = 13107kB
min_wal_size = 2GB
max_wal_size = 4GB
max_worker_processes = 4
max_parallel_workers_per_gather = 2