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Re: Better shared data structure management and resizable shared data structures

Heikki Linnakangas <hlinnaka@iki.fi>

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From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Andres Freund <andres@anarazel.de>, pgsql-hackers <pgsql-hackers@postgresql.org>, chaturvedipalak1911@gmail.com
Date: 2026-04-05T15:39:37Z
Lists: pgsql-hackers 
On 04/04/2026 19:32, Ashutosh Bapat wrote:
> test_shmem declares MODULE_big and OBJS which seems to be old
> fashioned, newer modules seem to be using MODULES. 

I don't think it's a matter of old or new. MODULE_big is used when you 
have multiple .o that are linked together into one .so file, while 
MODULES is used if each .o file is linked into a separate .so file. If 
there's only one .o file and .so file, then it doesn't really matter 
which you use, and I think we have examples of both.

> Also it should use NO_INSTALLCHECK.
> 
> /*
> * Alignment of the starting address. If not set, defaults to cacheline
> * boundary. Must be a power of two.
> */
> size_t alignment;
> 
> We don't seem to enforce the "must be a power of two" rule anywhere.
> We should at least validate it.

Will add.

- Heikki

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Tidy up #ifdef USE_INJECTION_POINTS guards

  2. Convert all remaining subsystems to use the new shmem allocation API

  3. Convert buffer manager to use the new shmem allocation functions

  4. Add alignment option to ShmemRequestStruct()

  5. Convert AIO to use the new shmem allocation functions

  6. Convert SLRUs to use the new shmem allocation functions

  7. Refactor shmem initialization code in predicate.c

  8. Use the new shmem allocation functions in a few core subsystems

  9. Convert lwlock.c to use the new shmem allocation functions

  10. Introduce a registry of built-in shmem subsystems

  11. Convert pg_stat_statements to use the new shmem allocation functions

  12. Add a test module to test after-startup shmem allocations

  13. Introduce a new mechanism for registering shared memory areas

  14. Move some code from shmem.c and shmem.h

  15. Improve test_lwlock_tranches

  16. Test pg_stat_statements across crash restart

  17. Refactor PredicateLockShmemInit to not reuse var for different things

  18. Refactor ShmemIndex initialization

  19. Add a new shmem_request_hook hook.