Re: SLRU optimization - configurable buffer pool and partitioning the SLRU lock

On Mon, Nov 20, 2023 at 4:42 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Mon, Nov 20, 2023 at 2:37 PM Andrey M. Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
>
> > > On 20 Nov 2023, at 13:51, Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> > >
> > > 2) Do we really need one separate lwlock tranche for each SLRU?
> > >
> > > IMHO if we use the same lwlock tranche then the wait event will show
> > > the same wait event name, right? And that would be confusing for the
> > > user, whether we are waiting for Subtransaction or Multixact or
> > > anything else. Is my understanding no correct here?
> >
> > If we give to a user multiple GUCs to tweak, I think we should give a way to understand which GUC to tweak when they observe wait times.

PFA, updated patch set, I have worked on review comments by Alvaro and
Andrey. So the only open comments are about clog group commit
testing, for that my question was as I sent in the previous email
exactly what part we are worried about in the coverage report?

The second point is, if we want to generate a group update we will
have to create the injection point after we hold the control lock so
that other processes go for group update and then for waking up the
waiting process who is holding the SLRU control lock in the exclusive
mode we would need to call a function ('test_injection_points_wake()')
to wake that up and for calling the function we would need to again
acquire the SLRU lock in read mode for visibility check in the catalog
for fetching the procedure row and now this wake up session will block
on control lock for the session which is waiting on injection point so
now it will create a deadlock. Maybe with bank-wise lock we can
create a lot of transaction so that these 2 falls in different banks
and then we can somehow test this, but then we will have to generate
16 * 4096 = 64k transaction so that the SLRU banks are different for
the transaction which inserted procedure row in system table from the
transaction in which we are trying to do the group commit

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