Re: Using base backup exclusion filters to reduce data transferred with pg_rewind

Greetings,

* Michael Paquier (michael@paquier.xyz) wrote:
> On Sat, Mar 24, 2018 at 11:14:34PM -0400, Tom Lane wrote:
> > Stephen Frost <sfrost@snowman.net> writes:
> >> I don't completely buy off on the argument that having these #define's
> >> would make it easier for forks (we've had quite a few folks fork PG, but
> >> how many of them have actually changed "base"?) and I'm on the fence
> >> about if these will make our lives simpler down the road when it comes
> >> to changing the directory names
> > 
> > I am distressed that nobody, apparently, is putting any weight on the
> > back-patching pain that will result from widespread replacement of path
> > names with macros.  I don't buy that either we or anyone else will need
> > to change these names in future, so I see pain and effectively no
> > gain.

While I agree that some consideration should be given to the impact a
change has on back-patching, I continue to be of the opinion that this
would be a good change, for the reasons which I outlined up-thread.
That said, I don't hold that position very strongly.

> That's actually something I worry about as well (as the author!), which
> is why I qualify the changes as intrusive.  At the end, I think that I
> would be tempted to just do #3, aka to keep a copy of the filter list in
> pg_rewind code while hardcoding a minimum of names and mention in both
> basebackup.c and pg_rewind code to not forget to update the filter list
> if necessary.  New paths in the data folder are not added on a monthly
> basis either, and not all of them can be filtered out so that's easy to
> maintain.

Intrusive, at least from my viewpoint, is more about how the code is
changed around and/or refactored than about the impact it has on
back-patching.  These are pretty mechanical changes, after all.

I'm not particularly thrilled with the idea of having two independent
lists of hard-coded paths to maintain, even with comments in both places
saying to update the other list.

Thanks!

Stephen