On Wed, Mar 13, 2019 at 11:54 AM Sergei Kornilov <sk@zsrv.org> wrote:
Hi
One new question from me: how about replication? Case: primary+replica, we shut down primary and enable checksum, and "started streaming WAL from primary" without any issue. I have master with checksums, but replica without. Or cluster with checksums, then disable checksums on primary, but standby think we have checksums.
Enabling or disabling the checksums offline on the master quite clearly requires a rebuild of the standby, there is no other way (this is one of the reasons for the online enabling in that patch, so I still hope we can get that done -- but not for this version).
You would have the same with PITR backups for example. And especially if you have some tool that does block or segment level differential.
Of course, we have to make sure that this actually fails.
I wonder if we should bring out the big hammer and actually change the system id in pg_control when checksums are enabled/disabled by this tool? That should make it clear to any tool that it's changed.
Also we support ./configure --with-blocksize=(not equals 8)? make check on HEAD fails for me. If we support this - i think we need recheck BLCKSZ between compiled pg_checksum and used in PGDATA
You mean if the backend and pg_checksums is built with different blocksize? Yeah, that sounds like something which is a cheap check and should be done.