Re: Changing the state of data checksums in a running cluster

On 8/29/25 16:26, Tomas Vondra wrote:
> ...
>
> I've seen these failures after changing checksums in both directions,
> both after enabling and disabling. But I've only ever saw this after
> immediate shutdown, never after fast shutdown. (It's interesting the
> pg_checksums failed only after fast shutdowns ...).
>

Of course, right after I send a message, it fails after a fast shutdown,
contradicting my observation ...

> Could it be that the redo happens to start from an older position, but
> using the new checksum version?
>

... but it also provided more data supporting this hypothesis. I added
logging of pg_current_wal_lsn() before / after changing checksums on the
primary, and I see this:

1) LSN before: 14/2B0F26A8
2) enable checksums
3) LSN after: 14/EE335D60
4) standby waits for 14/F4E786E8 (higher, likely thanks to pgbench)
5) standby restarts with -m fast
6) redo starts at 14/230043B0, which is *before* enabling checksums

I guess this is the root cause. A bit more detailed log attached.

regards

--
Tomas Vondra