Re: Including a sample Table Access Method with core code

On Mon, Jul 03, 2023 at 08:33:32PM +0200, Hannu Krosing wrote:
> One thing that was briefly mentioned (but is missing from the notes)
> is need to have a sample API client in contrib/ , both for having a
> 2nd user for API to make it more likely that non-heap AMs are doable
> and also to serve as an easy starting point for someone interested in
> developing a new AM.

That sounds like a fair thing to have, though templates may live
better under src/test/modules.

> There are a few candidates which could be lightweight enough for this
>
> * in-memory temp tables, especially if you specify max table size at
> creation and/or limit data types which can be used.
>
> * "overlay tables" - tables which "overlay" another - possibly
> read-only - table and store only changed rows and tombstones for
> deletions. (this likely would make more sense as a FDW itself as Table
> AM currently knows nothing about Primary Keys and these are likely
> needed for overlays)
>
> * Table AM as a (pl/)Python Class - this is inspired by the amazing
> Multicorn [2] FDW-in-Python tool which made it ridiculously easy to
> expose anything (mailbox, twitter feed, git commit history,
> you-name-it) as a Foreign Table

I cannot say how simple that is without seeing the code, but limiting
the use of an AM to be linked to a single session sounds like a
concept simple enough, limiting its relpersistence on the way. One
thing that may be also interesting is something that does not go
through the Postgres buffer pool.

> Included Mark Dilger directly to this mail as he mentioned he has a
> Perl script that makes a functional copy of heap AM that can be
> compiled as installed as custom AM.

Similar discussion has happened in 640c198 related to the creation of
dummy_index_am, where the argument is that such a module needs to
provide value in testing some of the core internals. dummy_index_am
did so for reloptions on indexes because there was not much coverage
for that part of the system.

> @mark - maybe you can create 3 boilerplate Table AMs for the above
> named `mem_am`, `overlay_am` and `py3_am` and we could put them
> somewhere for interested parties to play with ?

Not sure if that's worth counting, but I also have a table AM template
stored in my plugin repo:
https://github.com/michaelpq/pg_plugins/tree/main/blackhole_am

It does as much as its name states, being able to eat all the data fed
to it.
--
Michael