Re: Changing shared_buffers without restart

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.