On Fri, Jul 24, 2026 at 1:40 AM Xuneng Zhou <[email protected]> wrote: > > On Thu, Jul 23, 2026 at 11:08 PM Melanie Plageman > <[email protected]> wrote: > > > > > I wonder if in 20, we should move toward Andres' suggested formula > > Max(1, (num_temp_buffers − NLocalPinnedBuffers) / 4) > > instead of the existing > > num_temp_buffers / 4 − NLocalPinnedBuffers > > > > Which would mean we got a quarter of available buffers instead of a > > hard cap of a quarter of total buffers. > > This wouldn't have been any better at solving the issue in this > > thread, but I'm wondering if it is just a better formula in general > > going forward (not for backpatching). > > I am not sure about that. In the existing formula, we set a hard-cap > for the read streams at backend level. For the suggested one, the cap > is removed so multiple successive streams could push the water level > of pins toward the ceiling of temp buffers. I am unsure of the > consequences of this. Adjusting the cap limit alone seems not resolve > the competing nature between read stream and other needs. Reclaiming > some pinned buffers might help, but it is a more complex mechanism > which might not be a good fit in the bigger picture.
I think the right approach is to drive out a change like this with specific use cases or after seeing bottlenecks/problems in workloads. Since we're not encountering those now, I think investigating how to change this falls far down the priority list. - Melanie
