Re: Proposal: Limitations of palloc inside checkpointer

Hi, Tom!

Thanks for catching this.

On Thu, Aug 7, 2025 at 2:58 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Alexander Korotkov <aekorotkov(at)gmail(dot)com> writes:
> > I'm going to push this if no objections.
>
> I looked at these patches while preparing release notes, and
> found an oversight. CheckpointerShmemInit does
>
> CheckpointerShmem->max_requests = Min(NBuffers, MAX_CHECKPOINT_REQUESTS);
>
> but CheckpointerShmemSize still does
>
> size = add_size(size, mul_size(NBuffers, sizeof(CheckpointerRequest)));
>
> So if NBuffers is more than MAX_CHECKPOINT_REQUESTS, we will allocate
> extra CheckpointerRequest array entries that we will never use,
> wasting shared memory. Admittedly the amount is small relative to the
> shared buffers themselves, but at the very least this is confusing.
>
> The comment in CheckpointerShmemSize needs adjustment, too.

I attached a patch to fix it.

Best,
Xuneng