Re: Version control? You're soaking in it!

On Wed, May 04, 2005 at 03:09:42PM +0200, Dirk Schenkewitz wrote:
> Well. Normally I make comments like "improved handling of the
> Z-data, speeds up things a lot" and not "Changed handling of
> Z-data to speed things up, introduces a bug that will format all
> your filesystems if you delete a file between midnight and 0:30" -

But you should! As Andrew Morton wrote recently on the Linux Kernel
Development list:

    It's nice that patches are called "fix the frobnozzle gadget", but
    this analysis would be a lot easier if people would also label their
    patches "break the frobnozzle gadget" when that's what they do.

> Just HOW can you fall back to a known good state? As long as you
> don't know the cause of a certain problem? (After you found out, you
> don't need any version management at all - fix the problem and it's
> gone. :-)) Seriously - is/are there any method(s) that make it easier
> to find an *unknown* bug or rather find the *cause* for a certain
> problem, using some advantage of svn?

Develop a test case that shows the bug. Find an older version that
doesn't trigger the test failure. Now:

A. If you've got some idea of where the bug is, look at the modified
files for each changeset between "works" and HEAD. For those that touch
files under suspicion, look at the diffs. For suspicious changes, run
the test.

OR

B. If you're at a complete loss, it's binary search time. Pick a
revision between "works" and HEAD, call it T. Test it. If it passes,
then pick another between "T" and HEAD; if it fails, pick between
"works" and "T". Repeat.

(Not, I admit, a particular Subversion capability, just a nice property
of doing VC at all.)

Steve

-- 
"Outlook not so good." That magic 8-ball knows everything! I'll ask
about Exchange Server next.
                           -- (Stolen from the net)
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