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

Hi,

On Tue, 5 May 2026 at 19:16, Daniel Gustafsson <daniel(at)yesql(dot)se> wrote:

> > While further testing this feature, I realized that
> ProcessSingleRelationFork()
> > unconditionally called log_newpage_buffer() for every page of every
> relation
> > during pg_enable_data_checksums(). This included unlogged relations,
> > which by definition never generate WAL for data changes and are reset to
> their
> > init fork on any recovery.
>
>
> I've tested your patch, and also expanded the test you wrote a little with
> a
> persistence change.
>
>
I tested the patches, it mostly looks good.

I've a small concern in 0001. The new guard uses only
RelationNeedsWAL(reln),
but ProcessSingleRelationByOid() iterates all forks. For unlogged
relations,
the init fork is special, there are several existing call sites that
preserve
WAL for INIT_FORKNUM, for example using

RelationNeedsWAL(rel) || forknum == INIT_FORKNUM

and catalog/storage.c notes that unlogged init forks need WAL and sync.

So I think the condition in ProcessSingleRelationFork() should preserve the
init-fork case, e.g.

if (RelationNeedsWAL(reln) || forkNum == INIT_FORKNUM)
log_newpage_buffer(buf, false);

It would also be good to extend the new test so it exercises a non-empty
init
fork, perhaps with an unlogged table that has an index, and then verifies
the
standby/recovery behavior.

0002 and 0003 look good to me.

Regards,
Ayush