Horton

Re: Changing shared_buffers without restart

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Dmitry Dolgov <9erthalion6@gmail.com>
Cc: Thom Brown <thom@linux.com>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, Tomas Vondra <tomas@vondra.me>, Thomas Munro <thomas.munro@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Jack Ng <Jack.Ng@huawei.com>, Ni Ku <jakkuniku@gmail.com>
Date: 2025-07-14T14:23:23Z
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 →

  1. Remove PG_MMAP_FLAGS from mem.h

  2. Improve runtime and output of tests for replication slots checkpointing.

  3. Revert support for improved tracking of nested queries

  4. Use exported symbols list on macOS for loadable modules as well

  5. Add support for basic NUMA awareness

  6. Avoid unnecessary copying of a string in pg_restore.c

  7. aio: Infrastructure for io_method=worker

  8. Improve InitShmemAccess() prototype

Hi,

On 2025-07-14 16:01:50 +0200, Dmitry Dolgov wrote:
> > On Mon, Jul 14, 2025 at 09:42:46AM -0400, Andres Freund wrote:
> > What on earth would be the point of putting a buffer on the freelist but not
> > make it reachable by the clock sweep? To me that's just nonsensical.
> 
> To clarify, we're not talking about this scenario as "that's how it
> would work after the resize". The point is that to expand shared buffers
> they need to be initialized, included into the whole buffer machinery
> (freelist, clock sweep, etc.) and NBuffers has to be updated.

It seems pretty obvious to that the order has to be

1) initialize buffer headers
2) update NBuffers
3) put them onto the freelist

(with 3) hopefully becoming obsolete)


> Those steps are separated in time, and I'm currently trying to understand
> what are the consequences of performing them in different order and whether
> there are possible concurrency issues under various scenarios. Does this
> make more sense, or still not?

I still don't understand why it'd ever make sense to put a buffer onto the
freelist before updating NBuffers first.

Greetings,

Andres Freund