Re: like pg_shmem_allocations, but fine-grained for DSM registry ? - Mailing list pgsql-hackers

On Fri, Mar 14, 2025 at 4:16 PM Nathan Bossart <nathandbossart@gmail.com> wrote:

On Thu, Mar 13, 2025 at 06:54:09PM +0200, Florents Tselai wrote:
> I扉e been working with the DSM registry API.
> I was wondering if it is possible (it doesn愒 look like it) or if it has been discussed:
> can we expose a view like pg_shmem_allocations, but fine-grained for every named segment (i.e. created by GetNamedDSMSegment )?
>
> Currently, there is a "DSM Registry Data" entry in that view,
> but iiuc, it愀 only about the top-level hash table the registry uses.

This seems like a generally reasonable idea to me.  In theory, it should be
easy enough to build something that walks through the DSM registry hash
table.

 Here's a first attempt towards a view pg_dsm_registry(name, size) that does just that

So, using the test_dsm_registry module as a test bed, 

it would look like this. 

CREATE EXTENSION test_dsm_registry;
SELECT set_val_in_shmem(1236);
 set_val_in_shmem
------------------
 
(1 row)

-- 20 bytes = int (4 bytes) + LWLock (16bytes)
SELECT * FROM pg_dsm_registry;
       name        | size
-------------------+------
 test_dsm_registry |   20
(1 row)

I'll create a cf entry to keep track of this