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

On 2023-Nov-18, Dilip Kumar wrote:

> On Fri, Nov 17, 2023 at 6:16 PM Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:

> > I wonder what's the deal with false sharing in the new
> > bank_cur_lru_count array. Maybe instead of using LWLockPadded for
> > bank_locks, we should have a new struct, with both the LWLock and the
> > LRU counter; then pad *that* to the cacheline size. This way, both the
> > lwlock and the counter come to the CPU running this code together.
>
> Actually, the array lengths of both LWLock and the LRU counter are
> different so I don't think we can move them to a common structure.
> The length of the *buffer_locks array is equal to the number of slots,
> the length of the *bank_locks array is Min (number_of_banks, 128), and
> the length of the *bank_cur_lru_count array is number_of_banks.

Oh.

> > Looking at the coverage for this code,
> > https://coverage.postgresql.org/src/backend/access/transam/clog.c.gcov.html#413
> > it seems in our test suites we never hit the case where there is
> > anything in the "nextidx" field for commit groups. To be honest, I
> > don't understand this group stuff, and so I'm doubly hesitant to go
> > without any testing here. Maybe it'd be possible to use Michael
> > Paquier's injection points somehow?
>
> Sorry, but I am not aware of "Michael Paquier's injection" Is it
> something already in the repo? Can you redirect me to some of the
> example test cases if we already have them? Then I will try it out.

https://postgr.es/ZVWufO_YKzTJHEHW(at)paquier(dot)xyz

--
Álvaro Herrera 48°01'N 7°57'E — https://www.EnterpriseDB.com/
"Sallah, I said NO camels! That's FIVE camels; can't you count?"
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