Re: Re: Re: Enabling checksums on a streaming replica

Michael Paquier <michael(at)paquier(dot)xyz> wrote on 06/27/2019 11:17:10 PM:

> From: Michael Paquier <michael(at)paquier(dot)xyz>
> To: Brad Nicholson <bradn(at)ca(dot)ibm(dot)com>
> Cc: Grigory Smolkin <g(dot)smolkin(at)postgrespro(dot)ru>, pgsql-
> general(at)lists(dot)postgresql(dot)org
> Date: 06/27/2019 11:17 PM
> Subject: [EXTERNAL] Re: Re: Enabling checksums on a streaming replica
>
> On Wed, Jun 26, 2019 at 02:08:19PM -0400, Brad Nicholson wrote:
> > In testing, it doesn't appear to matter. I've ensured that I've
generated
> > some full page writes (confirmed via pg_waldump), and those apply
> > fine.
>
> Full pages writes are first written from shared buffers to WAL, where
> their checksums does not actually apply. When the WAL records are
> read an applied, a full page image is recovered in shared buffers.
> The checksum of the page would get updated once the shared buffer page
> used is evicted and written back to disk.
>

So if all the checksums are being recalculated on the replica, this
approach should be relatively safe, should it not?

Assuming pg_checksums is doing the right thing (and it looks to me like it
should be).

Brad.