Re: maintenance_work_mem used by Vacuum

On Wed, Oct 16, 2019 at 5:35 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Wed, Oct 16, 2019 at 3:48 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> >
> > It is not that currently, other indexes don't use any additional
> > memory (except for maintainence_work_mem). For example, Gist index
> > can use memory for collecting empty leaf pages and internal pages. I
> > am not sure if we can do anything for such cases. The case for Gin
> > index seems to be clear and it seems to be having the risk of using
> > much more memory, so why not try to do something for it?
>
> Yeah gin indexes is clear now and I agree that we need to do something
> for it. But I'm also concerned third party index AMs. Similar to the
> problem related to IndexBulkDeleteResult structure that we're
> discussing on another thread I thought that we have the same problem
> on this.
>

I understand your concern, but I am not sure what is a good way to
deal with it. I think we can do something generic like divide the
maintainence_work_mem equally among workers, but then the indexes that
use maintainence_work_mem will suffer if the number of such indexes is
much less than the indexes that don't use maintainence_work_mem.
Another idea could be each index AM tell whether it uses
maintainence_work_mem or not and based on that we can do the
computation (divide the maintainence_work_mem by the number of such
indexes during parallel vacuum). Do you have any other ideas for
this?

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