On 06.04.2010, at 10:06, Adam Barth wrote:
4) It's harder to isolate regressions if these appear and disappear
several times (aforementioned confusion doesn't help either).
Screening bugs about regressions also becomes more error-prone.
This arguments goes both ways though - it's even harder to isolate
regressions if the platform in question had broken build at the time.
Concretely, supposed we hadn't cleaned up the Tiger bot to be green
recently. I strongly suspect the regression caused by r57081 would
have been lost in the thought process that "the Tiger bot is always
red." Even though the regression was real and affected every
platform. Had we noticed the problem (say) a month later, we would
have had a devil of a time tracking down the issue as evidenced by the
effort required to fix the previous ancient Tiger-only failures.
I was talking about regressions not covered by regression tests. When
there is a bug about something that works in Safari 4, but not in ToT,
you often need to find out when exactly it broke - and if there were
several breakage points, it gets harder. Usually not by much, but
sometimes this can lead you astray, and then it costs a lot.
Again, this is not to say that we should never roll out patches, but
it's another cost to consider.
- WBR, Alexey Proskuryakov
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