Re: Is is safe to use SPI in multiple threads?

On Sun, Dec 11, 2016 at 2:39 PM, Qiu Xiafei <qiuxiafei(at)gmail(dot)com> wrote:
> Because of the one-backend-per-session concept of PG, I think I should bind
> one my DSL session to one bg worker only. It seems work. But is there a way
> to launch a bg worker when a new session starts, just like pg's
> per-session-backend do? Is it possible to run a bg worker for incoming
> sessions and to launch a new bg worker to handle the session when it comes?

There is the concept of dynamic background workers in Postgres. That's
what for example parallel query uses. At planning a number of workers
thought as suited is selected, and then spawned dynamically at
execution, at the limit defined by max_worker_processes though. Have a
look at worker_spi in the code tree, which is a module that does
present a way to spawn workers dynamically. This infrastructure could
allow for example anybody to re-create what autovacuum does with a
launcher process and workers created depending on what needs to be
cleaned up per database as a plugin.
--
Michael