Re: Parallel Inserts in CREATE TABLE AS

On Thu, May 27, 2021 at 9:43 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > I have read it but I think we should try to ensure practically what is
> > happening because it is possible that first time worker checked in FSM
> > without taking relation extension lock, it didn't find any free page,
> > and then when it tried to acquire the conditional lock, it got the
> > same and just extended the relation by one block. So, in such a case
> > it won't be able to use the newly added pages by another worker. I am
> > not sure any such thing is happening here but I think it is better to
> > verify it in some way. Also, I am not sure if just getting the info
> > about the relation extension lock is sufficient?
> >
>
> One idea to find this out could be that we have three counters for
> each worker which counts the number of times each worker extended the
> relation in bulk, the number of times each worker extended the
> relation by one block, the number of times each worker gets the page
> from FSM. It might be possible that with this we will be able to
> figure out why there is a difference between your and Hou-San's
> results.

Yeah, that helps. And also, the time spent in
LockRelationForExtension, ConditionalLockRelationForExtension,
GetPageWithFreeSpace and RelationAddExtraBlocks too can give some
insight.

My plan is to have a patch with above info added in (which I will
share it here so that others can test and see the results too) and run
the "case 4" where there's a regression seen on my system.

With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com