[Kde-scm-interest] Re: Usage of pull rebasing and merges

[Thiago Macieira]

On Wednesday, 9 de February de 2011 14:35:34 Johannes Sixt wrote:
> Take your example above. Name the '*' in the upper line between A and B z1
> to z9, and in the lower line y1 to y5. When you know A is good and B is
> bad, you only have to list the commits in any linearized order, for example,
> 
>   y1 z1 z2 y2 z3 z4 Z Y X z5 y3 z6 z7 y4 z8 z9 y5
> 
> and test the one in the middle. That happens to be X. It is a bad commit.
> At this point, you know that the regression was introduzed by one of z1,
> z2, z3, z4, Z, or X. Or if you picked Y, you would strike y1, y2, and Y
> from the list and repeat. See? You never have to know on "which branch"
> you are.

Hmm... Let me see if I understand:

Let's instead list the commits by their state: good and bad. Remember that all 
the y commits are good.

y1 z1 z2 y2 z3 z4 Z Y X z5 y3 z6 z7 y4 z8 z9 y5
G  G  G  G  G  G  G G B B  G  B  B  G  B  B  G

If I choose one of the z commits to the left of X (let's say, Z), they'll test 
Good, which means I can exclude the A-Z commits from my list. If I choose one 
of the z commits to the right of X, they'll test bad and I should exclude from 
there to B. If I choose a commit from the AYB branch (say, Y), and it tests 
good, I can only exclude A-Y, whe the remainder commits still left (y3 to y5).

So this is a bisection, but a weird one because you're still excluding less 
than half of the remaining commits, as you're jumping from branch to branch. 

Anyway, the point is made: since you are excluding less than half at each 
iteration, the number of iterations to find the culprit is actually bigger than 
a linear history.

-- 
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
  Senior Product Manager - Nokia, Qt Development Frameworks
      PGP/GPG: 0x6EF45358; fingerprint:
      E067 918B B660 DBD1 105C  966C 33F5 F005 6EF4 5358
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