I wrote:
> Interestingly, pg_verifybackup's t/003_corruption.pl test also fails
> with the same issue, so apparently this platform is even more
> aggressive about sparse-ifying files than Thomas' FreeBSD box.
> I wonder how come we managed to pass that test case before on
> these machines.
The answer to that seems to be that the test scripts for
pg_verifybackup simply fail to detect when it's mishandling
sparse tar entries. We only check failing cases not successful
cases, and in each case the error checked for is independent of
whether we would have extracted WAL data correctly. Grumble.
regards, tom lane