Re: pg_upgrade --copy-file-range

On Fri, Mar 22, 2024 at 10:40 AM Tomas Vondra
<tomas.vondra@enterprisedb.com> wrote:
> There's one question, though. As it stands, there's a bit of asymmetry
> between handling CopyFile() on WIN32 and the clone/copy_file_range on
> other platforms). On WIN32, we simply automatically switch to CopyFile
> automatically, if we don't need to calculate checksum. But with the
> other methods, error out if the user requests those and we need to
> calculate the checksum.

That seems completely broken. copy_file() needs to have the ability to
calculate a checksum if one is required; when one isn't required, it
can do whatever it likes. So we should always fall back to the
block-by-block method if we need a checksum. Whatever option the user
specified should only be applied when we don't need a checksum.

Consider, for example:

pg_basebackup -D sunday -c fast --manifest-checksums=CRC32C
pg_basebackup -D monday -c fast --manifest-checksums=SHA224
--incremental sunday/backup_manifest
pg_combinebackup sunday monday -o tuesday --manifest-checksums=CRC32C --clone

Any files that are copied in their entirety from Sunday's backup can
be cloned, if we have support for cloning. But any files copied from
Monday's backup will need to be re-checksummed, since the checksum
algorithms don't match. With what you're describing, it sounds like
pg_combinebackup would just fail in this case; I don't think that's
the behavior that the user is going to want.

--
Robert Haas
EDB: http://www.enterprisedb.com