Re: Changing shared_buffers without restart

Robert Haas <robertmhaas@gmail.com>

From: Robert Haas <robertmhaas@gmail.com>

To: Andres Freund <andres@anarazel.de>

Cc: Dmitry Dolgov <9erthalion6@gmail.com>, pgsql-hackers@postgresql.org

Date: 2024-11-28T01:28:59Z

Lists: pgsql-hackers

Commits

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

Remove PG_MMAP_FLAGS from mem.h
- c100340729b6 19 (unreleased) landed
Improve runtime and output of tests for replication slots checkpointing.
- 4464fddf7b50 18.0 cited
Revert support for improved tracking of nested queries
- f85f6ab051b7 18.0 cited
Use exported symbols list on macOS for loadable modules as well
- 3feff3916ee1 18.0 cited
Add support for basic NUMA awareness
- 65c298f61fc7 18.0 cited
Avoid unnecessary copying of a string in pg_restore.c
- 5e1915439085 18.0 cited
aio: Infrastructure for io_method=worker
- 55b454d0e140 18.0 cited
Improve InitShmemAccess() prototype
- 2a7b2d97171d 18.0 landed

On Wed, Nov 27, 2024 at 4:41 PM Andres Freund <andres@anarazel.de> wrote:
> Strictly speaking we don't actually need to map shared buffers to the same
> location in each process... We do need that for most other uses of shared
> memory, including the buffer mapping table, but not for the buffer data
> itself.

Well, if it can move, then you have to make sure it doesn't move while
someone's holding onto a pointer into it. I'm not exactly sure how
hard it is to guarantee that, but we certainly do construct pointers
into shared_buffers and use them at least for short periods of time,
so it's not a purely academic concern.

-- 
Robert Haas
EDB: http://www.enterprisedb.com