Re: pg_upgrade and rsync

On 1/27/15 9:32 PM, Bruce Momjian wrote
> Now, this isn't actually a problem for the first time that file is
> backed up- the issue is if that file isn't changed again. rsync won't
> re-copy it, but that change that rsync missed won't be in the WAL
> history for the *second* backup that's done (only the first), leading to
> a case where that file would end up corrupted.
> Interesting problem, but doesn't rsync use sub-second accuracy?
>
According to my empirical testing on Linux and OSX the answer is no:
rsync does not use sub-second accuracy. This seems to be true even on
file systems like ext4 that support millisecond mod times, at least it
was true on Ubuntu 12.04 running ext4.

Even on my laptop there is a full half-second of vulnerability for
rsync. Faster systems may have a larger window.

--
- David Steele
david(at)pgmasters(dot)net