Re: Comments on Custom RMGRs

On Fri, 2022-05-13 at 13:31 +0100, Simon Riggs wrote:
> The first was a discussion about a data structure needed by BDR about
> 4 years ago. In the absence of a pluggable checkpoint, the solution
> was forced to use a normal table, which wasn't very satisfactory.

I'm interested to hear more about this case. Are you developing it into
a full table AM? In my experience with columnar, there's still a long
tail of things I wish I had in the backend to better support complete
table AMs.

> The second was a more recent conversation with Mike Stonebraker, at
> the end of 2021.. He was very keen to remove the buffer manager
> entirely, which requires that we have a new smgr, which then needs
> new
> code to allow it to be written to disk at checkpoint time, which then
> requires some kind of pluggable code at checkpoint time. (Mike was
> also keen to remove WAL, but that's another story entirely!).

I'm guessing that would be more of an experimental/ambitious project,
and based on modified postgres anyway.

> The last use case was unlogged indexes, which need to be read from
> disk at startup or rebuilt after crash, which requires RmgrStartup to
> work both with and without InRedo=true.

That sounds like a core feature, in which case we can just refactor
that for v16. It might be a nice cleanup for unlogged tables, too. I
don't think your 002-v2 patch is particularly risky, but any reluctance
at all probably pushes it to v16 given that it's so late in the cycle.

Regards,
Jeff Davis