I think planner would also benefit from threads. There are many tasks
in planner that are independent and can be scheduled using dependency
graph. They are too small to be parallelized through separate backends
but large enough to be performed by threads. Planning queries
involving partitioned tables take longer time (in seconds) esp. when
there are thousands of partitions. That kind of planning will get
immensely benefited by threading. Of course we can use backends which
can pull tasks from queue but sharing the PlannerInfo and its
substructure is easier through the same address space rather than
shared memory.
On Sat, Jun 10, 2023 at 5:25 AM Bruce Momjian <bruce@momjian.us> wrote:
>
> On Wed, Jun 7, 2023 at 06:38:38PM +0530, Ashutosh Bapat wrote:
> > With multiple processes, we can use all the available cores (at least
> > theoretically if all those processes are independent). But is that
> > guaranteed with single process multi-thread model? Google didn't throw
> > any definitive answer to that. Usually it depends upon the OS and
> > architecture.
> >
> > Maybe a good start is to start using threads instead of parallel
> > workers e.g. for parallel vacuum, parallel query and so on while
> > leaving the processes for connections and leaders. that itself might
> > take significant time. Based on that experience move to a completely
> > threaded model. Based on my experience with other similar products, I
> > think we will settle on a multi-process multi-thread model.
>
> I think we have a few known problem that we might be able to solve
> without threads, but can help us eventually move to threads if we find
> it useful:
>
> 1) Use threads for background workers rather than processes
> 2) Allow sessions to be stopped and started by saving their state
>
> Ideally we would solve the problem of making shared structures
> resizable, but I am not sure how that can be easily done without
> threads.
>
> --
> Bruce Momjian <bruce@momjian.us> https://momjian.us
> EDB https://enterprisedb.com
>
> Only you can decide what is important to you.
--
Best Wishes,
Ashutosh Bapat