Re: Changing shared_buffers without restart

Hi,

On 2025-07-14 15:08:28 +0200, Dmitry Dolgov wrote:
> > On Mon, Jul 14, 2025 at 08:56:56AM -0400, Andres Freund wrote:
> > > 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.
>
> 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.

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

Greetings,

Andres Freund