Re: Proposal to add page headers to SLRU pages

On Thu, Dec 7, 2023 at 1:28 PM Debnath, Shawn <sdn(at)ebay(dot)com> wrote:
> What is being proposed now is the simple and core functionality of introducing
> page headers to SLRU pages while continuing to be in the SLRU cache. This
> allows the whole project to be iterative and reviewers to better reason about
> the smaller set of changes being introduced into the codebase.
>
> Once the set of on-disk changes are in, we can follow up on optimizations.
> It may be moving to buffer cache or reviewing Dilip's approach in [1], we
> will have the option to be flexible in our approach.

I basically agree with this. I don't think we should let the perfect
be the enemy of the good. Shooting down this patch because it doesn't
do everything that we want is a recipe for getting nothing done at
all.

That said, I don't think that the original post on this thread
provides a sufficiently clear and detailed motivation for making this
change. For this to eventually be committed, it's going to need (among
other things) a commit message that articulates a convincing rationale
for whatever changes it makes. Here's what the original email said:

> It adds a checksum to each SLRU page, tracks page LSN as if it is a standard page and eases future page enhancements.

Of those three things, in my opinion, the first is good and the other
two are too vague. I assume that most people who would be likely to
read a commit message would understand the value of pages having
checksums. But I can't immediately think of what the value of tracking
the page LSN as if it were a standard page might be, so that probably
needs more explanation. Similarly, at least one or two of the future
page enhancements that might be eased should be spelled out, and/or
the ways in which they would be made easier should be articulated.

--
Robert Haas
EDB: http://www.enterprisedb.com