Re: [HACKERS] Block level parallel vacuum

On Wed, Nov 20, 2019 at 11:01 AM Masahiko Sawada
<masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
>
> I've attached the latest version patch set. The patch set includes all
> discussed points regarding index AM options as well as shared cost
> balance. Also I added some test cases used all types of index AM.
>
> During developments I had one concern about the number of parallel
> workers to launch. In current design each index AMs can choose the
> participation of parallel bulk-deletion and parallel cleanup. That
> also means the number of parallel worker to launch might be different
> for each time of parallel bulk-deletion and parallel cleanup. In
> current patch the leader will always launch the number of indexes that
> support either one but it would not be efficient in some cases. For
> example, if we have 3 indexes supporting only parallel bulk-deletion
> and 2 indexes supporting only parallel index cleanup, we would launch
> 5 workers for each execution but some workers will do nothing at all.
> To deal with this problem, I wonder if we can improve the parallel
> query so that the leader process creates a parallel context with the
> maximum number of indexes and can launch a part of workers instead of
> all of them.
>

Can't we choose the number of workers as a maximum of
"num_of_indexes_that_support_bulk_del" and
"num_of_indexes_that_support_cleanup"? If we can do that, then we can
always launch the required number of workers for each phase (bulk_del,
cleanup). In your above example, it should choose 3 workers while
creating a parallel context. Do you see any problem with that?

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com