Re: MultiXact\SLRU buffers configuration

Hi Andrey,

On Sat, Mar 13, 2021 at 1:44 AM Andrey Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
> [v10]

+int multixact_offsets_slru_buffers = 8;
+int multixact_members_slru_buffers = 16;
+int subtrans_slru_buffers = 32;
+int notify_slru_buffers = 8;
+int serial_slru_buffers = 16;
+int clog_slru_buffers = 0;
+int commit_ts_slru_buffers = 0;

I don't think we should put "slru" (the name of the buffer replacement
algorithm, implementation detail) in the GUC names.

+ It defaults to 0, in this case CLOG size is taken as
<varname>shared_buffers</varname> / 512.

We already know that increasing the number of CLOG buffers above the
current number hurts as the linear search begins to dominate
(according to the commit message for 5364b357), and it doesn't seem
great to ship a new feature that melts your CPU when you turn it up.
Perhaps, to ship this, we need to introduce a buffer mapping table? I
have attached a "one coffee" attempt at that, on top of your v10 patch
(unmodified), for discussion. It survives basic testing but I don't
know how it performs.