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: 2025-07-14T12:56:56Z
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 11:32:25 +0200, Dmitry Dolgov wrote:
> > On Mon, Jul 14, 2025 at 10:24:50AM +0100, Thom Brown wrote:
> > On Mon, 14 Jul 2025, 09:54 Dmitry Dolgov, <9erthalion6@gmail.com> wrote:
> >
> > > > On Mon, Jul 14, 2025 at 01:55:39PM +0530, Ashutosh Bapat wrote:
> > > > > You're right of course, a buffer id could be returned from the
> > > > > ClockSweep and from the custom strategy buffer ring. Buf from what I
> > > see
> > > > > those are picking a buffer from the set of already utilized buffers,
> > > > > meaning that for a buffer to land there it first has to go through
> > > > > StrategyControl->firstFreeBuffer, and hence the idea above will be a
> > > > > requirement for those as well.
> > > >
> > > > That isn't true. A buffer which was never in the free list can still
> > > > be picked up by clock sweep.
> > >
> > > How's that?
> > >
> >
> > Isn't it its job to find usable buffers from the used buffer list when no
> > free ones are available? The next victim buffer can be selected (and
> > cleaned if dirty) and then immediately used without touching the free list.
> 
> Ah, I see what you mean folks. But I'm talking here only about buffers
> which will be allocated after extending shared memory -- they  must go
> through the freelist first (I don't see why not, any other options?),
> and clock sweep will have a chance to pick them up only afterwards. That
> makes the freelist sort of an entry point for those buffers.

Clock sweep can find any buffer, independent of whether it's on the freelist.