Hey, all, As part of configuring the max_worker_processes parameter I would like to know how many current worker processes are active, but I'm unsure of the best way to do this. pg_stat_activity has a column backend_type which normally takes one of the following values: autovacuum launcher autovacuum worker logical replication launcher logical replication worker parallel worker background writer client backend checkpointer startup walreceiver walsender walwriter But extensions can launch additional processes and set this to a custom value as well. (pglogical, as an example, does this.) To the best of my understanding, only processes with a backend type set to "logical replication worker" or "parallel worker" count towards max_worker_processes, as well as any processes started by an extension that have backend_type set to any value other than the above values. I believe that, despite having "worker" in the name, an "autovacuum worker" process does not count towards max_worker_processes, correct? So I believe the following query should return the number of processes that count towards max_worker_processes. SELECT COUNT(*) FROM pg_catalog.pg_stat_activity WHERE backend_type NOT IN ( 'autovacuum launcher', 'autovacuum worker', 'logical replication launcher', -- 'logical replication worker', -- This is a worker process! -- 'parallel worker', -- This is a worker process! 'background writer', 'client backend', 'checkpointer', 'startup', 'walreceiver', 'walsender', 'walwriter' ); Is there a better way to do this? Also, in 9.6 and earlier, pg_stat_activity doesn't have a backend_type column, so I'm really unsure how to calculate this in those older versions. I think pglogical is pretty much the only extension that creates background workers on a regular basis, so I think I can have a rough approximation by checking the application_name instead for "pglogical", but I'd prefer a less hacky approach. On a related note, can anyone verify that all processes that count towards max_wal_senders will have backend_type set to "walsender", and all processes that count towards max_connections will have backend_type set to "client backend"? I think it might be useful to have additional columns added to pg_stat_activity that indicate which resource limits each process contributes to. max_worker_processes -> isworker max_wal_senders -> iswalsender max_connections -> isconn superuser_reserved_connections -> issuconn (You could then get the non-superuser connections via COUNT(*) FILTER (WHERE isconn) - COUNT(*) FILTER (WHERE issuconn) .) These two might also be useful, but I imagine using backend_type is pretty fool proof for these: max_logical_replication_workers -> islogrepworker max_parallel_workers -> isparallel Thanks, Paul
