Thomas Kellerer <> writes:
> for some reason pg_upgrade failed on Windows 10 for me, with an error message 
> that one specifc _vm file couldn't be copied.

Hmm ... a _vm file would go through rewriteVisibilityMap(), which is new
code for 9.6 and hasn't really gotten that much testing.  Its error
reporting is shamefully bad --- you can't tell which step failed, and
I wouldn't even put a lot of faith in the errno being meaningful,
considering that it does close() calls before capturing the errno.

But what gets my attention in this connection is that it doesn't
seem to be taking the trouble to open the files in binary mode.
Could that lead to the reported failure?  Not sure, but it seems
like at the least it could result in corrupted VM files.

Has anyone tested vismap upgrades on Windows, and made an effort
to validate that the output wasn't garbage?

                        regards, tom lane

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