Re: [HACKERS] Block level parallel vacuum

On Tue, Oct 29, 2019 at 12:37 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> I realized that v31-0006 patch doesn't work fine so I've attached the
> updated version patch that also incorporated some comments I got so
> far. Sorry for the inconvenience. I'll apply your 0001 patch and also
> test the total delay time.
>
While reviewing the 0002, I got one doubt related to how we are
dividing the maintainance_work_mem

+prepare_index_statistics(LVShared *lvshared, Relation *Irel, int nindexes)
+{
+ /* Compute the new maitenance_work_mem value for index vacuuming */
+ lvshared->maintenance_work_mem_worker =
+ (nindexes_mwm > 0) ? maintenance_work_mem / nindexes_mwm :
maintenance_work_mem;
+}
Is it fair to just consider the number of indexes which use
maintenance_work_mem? Or we need to consider the number of worker as
well. My point is suppose there are 10 indexes which will use the
maintenance_work_mem but we are launching just 2 workers then what is
the point in dividing the maintenance_work_mem by 10.

IMHO the calculation should be like this
lvshared->maintenance_work_mem_worker = (nindexes_mwm > 0) ?
maintenance_work_mem / Min(nindexes_mwm, nworkers) :
maintenance_work_mem;

Am I missing something?

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com