On Thu, 5 Mar 2026 at 20:56, Melanie Plageman <[email protected]> wrote: > > Today Andres and I noticed that heap_{update,insert,delete}() don't > register the VM buffer when they are clearing the VM. I was under the > impression that any buffers modified needed to be registered in the > WAL record. Without which, you'll never do an FPI. It seems like this > could cause checksum failures. What are we missing?
Might it be, because zeroing a VM page (which you would do when you encounter checksum failures) is an MVCC-safe operation? I agree with you that we probably _should_ register the VM (and possibly FSM) buffer, but that's a bit of a different story. Right now, the VM does not use the standard page format (nor does the FSM), and therefore every FPI would be the full 8KB, even when just a few bits of the VM page are in use; which would be a rather large waste of space. On Thu, 5 Mar 2026 at 21:16, Andres Freund <[email protected]> wrote: > > But it does seem like it could be a problem for incremental backup / > walsummarizer? I don't think it is, because that doesn't do calculations for non-main forks, it considers those forks always changed and includes them in full. Or at least, that was the response I got when I raised concerns about the FSM back when the incremental backup feature was being developed [0]. Kind regards, Matthias van de Meent Databricks (https://databricks.com) [0] https://postgr.es/m/CA%2BTgmoaR8o%2BPBeWc_2Ge0XVgoM7xWKNyDmqXoTov%3DS6_J1gecQ%40mail.gmail.com
