Re: Online enabling of checksums

Hi,

On 2018-08-01 21:03:22 +0300, Sergei Kornilov wrote:
> > They fail over to a secondary to do maintenance on a primary.
> But this is not problem even in current patch state. We can restart replica before failover and it works. I tested
thisbehavior during my review.
 
> We can:
> - call pg_enable_data_checksums() on master
> - wait change data_checksums to inprogress on replica

That's *precisely* the problem. What if your replicas are delayed
(e.g. recovery_min_apply_delay)? How would you schedule that restart
properly?  What if you later need to do PITR?


> - restart replica - we can restart replica before promote, right?
> - promote this replica
> - checksum helper is launched now and working on this promoted cluster

This doesn't test the consequences of the restart being skipped, nor
does it review on a code level the correctness.

Greetings,

Andres Freund