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.

> The one thing I'm not sure of, when verifying checksums via pg_checksums I
> see blocks being skipped. I'm not sure what or why it is skipping blocks,
> and if that indicates a problem or not.

Some files can get skipped entirely, but all the blocks of a file
are basically checked. Well, except for new pages of course which
have no checksums to look at yet.
--
Michael