Re: pgsql: Allow on-line enabling and disabling of data checksums

On Fri, Apr 6, 2018 at 5:35 AM, Magnus Hagander <magnus@hagander.net> wrote:
> Allow on-line enabling and disabling of data checksums
>
> This makes it possible to turn checksums on in a live cluster, without
> the previous need for dump/reload or logical replication (and to turn it
> off).
>
> Enabling checkusm starts a background process in the form of a
> launcher/worker combination that goes through the entire database and
> recalculates checksums on each and every page. Only when all pages have
> been checksummed are they fully enabled in the cluster. Any failure of
> the process will revert to checksums off and the process has to be
> started.
>
> This adds a new WAL record that indicates the state of checksums, so
> the process works across replicated clusters.
>


This has broken the buildfarm's cross-version upgrade testing (yes, we
do it for same-version upgrade as well as previous version upgrade).

For now I have fixed crake by adding code to disable checksums in the
saved cluster. That at least will send crake green. Not sure if it's
the fix we want, though. Maybe we should test if checksums are enabled
on the upgraded cluster and if so enable them on the new cluster via
initdb. When we decide on the best fix I will put out a new release.