Re: Enable data checksums by default

On 5/23/25 11:25, Daniel Gustafsson wrote:
>> On 23 May 2025, at 10:10, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
>
>> Aside from just documenting it, I see two things we could do:
>>
>> 1. Have pg_upgrade run initdb for you. It's always felt silly that you need to run initdb with the new version yourself, when there's really only one correct way to do it. pg_upgrade has all the checks to verify that you did it right, so why doesn't it just do it itself? I think that'd be a good long-term solution. Might be too late for 18, but I'm not sure. If someone wrote the patch we could evaluate it. To use that mode, the scripts calling pg_upgrade would need to be changed, though, so we'd perhaps want to do #2 or something else in addition to this.
>
> I can see this being desired longer term, but as you mention there is likely to
> be many moving parts outside of our immediate control making it much harder
> than just adding the call to initdb. It doesn't seem like a post-beta patch to
> me given the implications for packagers and others in the ecosystem.
>
>> 2. If the new cluster has checksums enabled, but the old one has them disabled, have pg_upgrade disable checksums in the new cluster.
>
> IF we do this it should be Very visible, since a user otherwise might think
> that their upgraded cluster will have checksums since they added them in
> initdb.
>

What counts as "very visible"? Would it be fine if the pg_upgrade docs
say this clearly, and pg_upgrade prints a warning? To me that seems
sufficient.

TBH I can't quite imagine people expecting checksums to just magically
appear after upgrade.

> I think we should document how to deal with checksums in upgrades, and perhaps
> even tweak the errormessage in the pg_upgrade check with explanatory comments
> if needed, and leave the functionality as is today.
>

Isn't that just an unnecessary breakage of existing tooling? I mean,
there's pretty much just one thing the user can do to make it work, and
that's disabling checksums. Sure, they might also enable checksums on
the old cluster, but that makes the upgrade much longer, and presumably
they use pg_upgrade to upgrade quickly.

That being said, I don't feel very strongly about this, so if the
consensus is to just error-out, so be it.

regards

--
Tomas Vondra