Re: better page-level checksums

On Tue, Jun 14, 2022 at 10:21:16PM -0400, Robert Haas wrote:
> On Tue, Jun 14, 2022 at 9:56 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
>> Technically we don't already do that today, with the 16-bit checksums
>> that are stored in PageHeaderData.pd_checksum. But we do something
>> equivalent: low-level tools can still infer that checksums must not be
>> enabled on the page (really the cluster) indirectly in the event of a
>> 0 checksum. A 0 value can reasonably be interpreted as a page from a
>> cluster without checksums (barring page corruption). This is basically
>> reasonable because our implementation of checksums is guaranteed to
>> not generate 0 as a valid checksum value.
>
> I don't think that 'pg_checksums -d' zeroes the checksum values on the
> pages in the cluster.

Saving the suspense.. pg_checksums --disable only updates the control
file to keep the operation cheap.
--
Michael