Re: Online verification of checksums

On Mon, Mar 18, 2019 at 2:06 AM Michael Paquier <michael(at)paquier(dot)xyz> wrote:
> The mentions on this thread that the server has all the facility in
> place to properly lock a buffer and make sure that a partial read
> *never* happens and that we *never* have any kind of false positives,
> directly preventing the set of issues we are trying to implement
> workarounds for in a frontend tool are rather good arguments in my
> opinion (you can grep for BufferDescriptorGetIOLock() on this thread
> for example).

Yeah, exactly. It may be that there is a good way to avoid those
issues without interacting with the server and that would be nice, but
... as far as I can see, nobody's figured out a way that's reliable
yet, and all of the solutions proposed so far basically amount to
"let's ignore things that might be serious problems because they might
be transient" and/or "let's retry and see if the problem goes away."
I'm more sanguine about a retry-based solution than an
ignore-possible-problems solution, but what's been proposed so far
seems quite prone to retrying so fast that it makes no difference, and
it's not clear how much code complexity we'd have to add to do better
or how reliable it would be even then.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company