Re: Changing shared_buffers without restart

Dmitry Dolgov <9erthalion6@gmail.com>

From: Dmitry Dolgov <9erthalion6@gmail.com>

To: Andres Freund <andres@anarazel.de>

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: 2025-07-14T13:20:03Z

Lists: pgsql-hackers

> On Mon, Jul 14, 2025 at 09:14:26AM -0400, Andres Freund wrote:
> > > Clock sweep can find any buffer, independent of whether it's on the freelist.
> >
> > It does the search based on nextVictimBuffer, where the actual buffer
> > will be a modulo of NBuffers, right? If that's correct and I get
> > everything else right, that would mean as long as NBuffers stays the
> > same (which is the case for the purposes of the current discussion) new
> > buffers, allocated on top of NBuffers after shared memory increase, will
> > not be picked by the clock sweep.
>
> Are you tell me that you'd put "new" buffers onto the freelist, before you
> increase NBuffers? That doesn't make sense.

Why?

> Orthogonaly - there's discussion about simply removing the freelist.

Good to know, will take a look at that thread, thanks.