Re: PostgreSQL 18.6/17.11: standby PANIC on restart after VM truncation

Hi Jacky and Kirill,

Melanie's v2-0002 in the VM clear thread [1] is the same change as
candidate (a), and it fixes this report too. On master the attached test
fails without it and passes with it. The same change also passes on 17,
18 and 19.

This does not need a switchover. With full_page_writes = off, a plain
standby restart hits it if the restartpoint is before a DELETE or UPDATE
that cleared VM bits and a later VACUUM truncated the VM. So it would be
good to get v2-0002 in before the next minor release.

I asked Fable to create a test for me.

The attached clears VM bits by delete, HOT update
and cross-page update, and fails if any one of the three reads still uses
RBM_NORMAL.

Candidate (b) would also work, but once the read no longer uses
RBM_NORMAL, no invalid page is logged for the VM, so it is not needed.

Until the fix ships, ignore_invalid_pages = on lets the standby start. It
can be turned off after the next restartpoint.

[1]
https://postgr.es/m/CAAKRu_bApoksLDb-HX0GYciU3uLWqA1JagntaV8GP0%3D%2BidehHw%40mail.gmail.com

Thanks,
Shihao