Re: [HACKERS] Block level parallel vacuum

On Wed, Nov 6, 2019 at 2:01 PM Mahendra Singh <mahi6run(at)gmail(dot)com> wrote:
>
> Hi
> I took all attached patches(v32-01 to v32-4) and one Dilip's patch from "Questions/Observations related to Gist vacuum" mail thread. On the top of all these patches, I created one more patch to test parallel vacuum functionally for all existence test suite.
> For reference, I am attaching patch.
>
> What does this patch?
> As we know that if we give parallel option with vacuum, then only we are vacuuming using parallel workers. So to test, I used existence guc force_parallel_mode and tested parallel vacuuming.
>
> If force_parallel_mode is set as regress, then if parallel option is not given with vacuum, I am forcing to use parallel workers for vacuum. If there is only one index and parallel degree is not given with vacuum(or parallel option is not given), and force_parallel_mode = regress, then I am launching one parallel worker(I am not doing work by leader in this case), but if there is more than one index, then i am using leader as a worker for one index and launching workers for all other indexes.
>
> After applying this patch and setting force_parallel_mode = regress, all test cases are passing (make-check world)
>
> I have some questions regarding my patch. Should we do vacuuming using parallel workers even if force_parallel_mode is set as on, or we should use new GUC to test parallel worker vacuum for existence test suite?

IMHO, with force_parallel_mode=on we don't need to do anything here
because that is useful for normal query parallelism where if the user
thinks that the parallel plan should have been selected by the planer
but planer did not select the parallel plan then the user can force
and check. But, vacuum parallelism is itself forced by the user so
there is no point in doing it with force_parallel_mode=on. However,
force_parallel_mode=regress is useful for testing the vacuum with an
existing test suit.

>
> Please let me know your thoughts for this patch.

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