Re: [Monotone-devel] Re: results of mercurial user survey

[Richard Levitte - VMS Whacker]

In message <address@hidden> on Fri, 28 Apr 2006 08:29:44 +0200, Jon Bright 
<address@hidden> said:

jon> I'll avoid quoting your whole mail, since I'm not replying to
jon> anything specific.  I see your point about the safety.  Safety is
jon> good, and I like it.  But:
jon> 
jon>   - The load of checking the validity of the database being
jon>     shifted to new users doing pulls seems to be the wrong place
jon>     to do it.  Couldn't we instead throw warnings at people on
jon>     start "Your database hasn't been checked for X days!  Run 'db
jon>     check'!"?

How long will it take before people start simply ignoring it?

jon>   - Doing the detection on the user side, we're detecting two
jon>     classes of problems: first, semantic problems in the DB on
jon>     the remote side and second, transmission problems (at
jon>     whichever layer) between remote and user.
jon> 
jon>   - The semantic problems aren't under the user's control - if
jon>     you're lucky, he writes a mail about them.  But you're
jon>     relying on something that seems like a pretty poor
jon>     communication path to discover your problems with old data.

The positive thing with having it done as it is done currently is that
it's more instantaneous.  Even if some users do not complain, I'm sure
a sufficiently large (basically, more than 0) percentage will, and
that should be enough to put responsible people on alert.

The alternative, and this is especially important on servers, is that
someone will have to spend time reading the logs, or reading some
report done with "db check".  While that sounds fine and doable,
experience from a number of sysadmin jobs show that logs are often
only checked when a problem has been discovered, or read more and more
carelessly because it looks like the same damn pattern all the time.
So we basically get back to discovery.

The thing with a distributed system is exactly that, that it's
distributed.  If an error occurs somewhere and remains undetected, it
will be trasmitted to everyone involved.  In monotone's case, it would
be everyone that does a pull.  At that point, it will be very
difficult to change it, since it might be pushed around, so any
correction that you do locally might be "corrected" back to the
erroneous state.

>From that point of view, it's probably a lot better for any monotone
instance to detect problems and refuse to store them locally.  That
makes the problem contained in the database where it resides instead
of having it propagate all over the place.

jon>   - The transmission problems seem like they should be detectable
jon>     with some simple SHAing.

I haven't really looked, but I was under the impression that there is
some kind of HMAC authentication in place.  No?

Cheers,
Richard

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Richard Levitte                         address@hidden
                                        http://richard.levitte.org/

"When I became a man I put away childish things, including
 the fear of childishness and the desire to be very grown up."
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