Re: max_parallel_workers can't actually be set?

Hi,

On 2019-08-17 13:41:18 -0400, Tom Lane wrote:
> Try this:
> alter system set max_parallel_workers = 20;
> and restart the system.
>
> max_parallel_workers is still 8, according to both SHOW and
> pg_controldata, nor can you launch more than 8 workers.

Hm. I can't reproduce that. I do get whatever number I configure. Note
also that pg_controldata shows max_worker_processes, not
max_parallel_workers.

> Even odder, if you just do
>
> regression=# set max_parallel_workers = 200;
> SET
> regression=# show max_parallel_workers;
> max_parallel_workers
> ----------------------
> 200
> (1 row)
>
> which should certainly not happen for a PGC_POSTMASTER parameter.

It's not PGC_POSTMASTER. That's max_worker_processes. The max_parallel_*
GUCs just control how many of max_worker_processes are used for $task.

Greetings,

Andres Freund