[PATCH 4/5] cli: add global option "--uuid"

[Daniel Schoepe]

On Sun, 09 Aug 2015 11:24+0200, David Bremner wrote:
> +    ``--uuid=HEX``
> +       Enforce that the database UUID (a unique identifier which
> +       persists until e.g. the database is compacted)
> +       is HEX; exit with an error if it is not. This is useful to
> +       detect rollover in modification counts on messages. You can
> +       find this UUID in the first column of output from
> +       ``notmuch count --output=modifications``

I think it's not entirely clear what the connection between the UUID and
the revisions on messages is. For example, compacting a database
shouldn't make a difference "extensionally", so the naive assumption
might be that the UUID, or, maybe more importantly, the revision counts
don't change.

For example, if lastmod queries are used to incrementally back up or
synchronize tags, then it doesn't matter if the database got compacted,
all one cares about are the changes to messages' tags since an earlier
point.

Based on quick experiments, it seems that the revisions don't change
when compacting the database; is this something that the patches
guarantee or a coincidence?

Best regards,
Daniel