Re: pg_upgrade --copy-file-range

On Fri, Mar 22, 2024 at 8:26 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> Hmm, this discussion seems to assume that we only use
> copy_file_range() to copy/clone whole segment files, right? That's
> great and may even get most of the available benefit given typical
> databases with many segments of old data that never changes, but... I
> think copy_write_range() allows us to go further than the other
> whole-file clone techniques: we can stitch together parts of an old
> backup segment file and an incremental backup to create a new file.
> If you're interested in minimising disk use while also removing
> dependencies on the preceding chain of backups, then it might make
> sense to do that even if you *also* have to read the data to compute
> the checksums, I think? That's why I mentioned it: if
> copy_file_range() (ie sub-file-level block sharing) is a solution in
> search of a problem, has the world ever seen a better problem than
> pg_combinebackup?

That makes sense; it's just a different part of the code than I
thought we were talking about.

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