When I run:
git bisect start <bad_commit> <good_commit>
I get:
Bisecting: 9727 revisions left to test after this (roughly 13 steps)
But the bad_commit and good_commit I specified are clearly only around 50 commits back in history. I did a "git log" and saw both of the commits there. I also verified the bad commit is more recent than the good commit.
What's going on here?
If you merged in a long-lived branch bisect by default will hunt through the whole branch. Easy way to wall off the side histories is to add --first-parent, that'll tell you the merge that brought the bug.