Re: introduce dynamic shared memory registry

Hi, all

I see most xxxShmemInit functions have the logic to handle IsUnderPostmaster env.
Do we need to consider it in DSMRegistryShmemInit() too? For example, add some assertions.
Others LGTM.

Zhang Mingli
www.hashdata.xyz
On Dec 5, 2023 at 11:47 +0800, Nathan Bossart <nathandbossart(at)gmail(dot)com>, wrote:
> Every once in a while, I find myself wanting to use shared memory in a
> loadable module without requiring it to be loaded at server start via
> shared_preload_libraries. The DSM API offers a nice way to create and
> manage dynamic shared memory segments, so creating a segment after server
> start is easy enough. However, AFAICT there's no easy way to teach other
> backends about the segment without storing the handles in shared memory,
> which puts us right back at square one.
>
> The attached 0001 introduces a "DSM registry" to solve this problem. The
> API provides an easy way to allocate/initialize a segment or to attach to
> an existing one. The registry itself is just a dshash table that stores
> the handles keyed by a module-specified string. 0002 adds a test for the
> registry that demonstrates basic usage.
>
> I don't presently have any concrete plans to use this for anything, but I
> thought it might be useful for extensions for caching, etc. and wanted to
> see whether there was any interest in the feature.
>
> --
> Nathan Bossart
> Amazon Web Services: https://aws.amazon.com