<s>
Bisection	B-Protocol
is	O
a	O
method	O
used	O
in	O
software	O
development	O
to	O
identify	O
change	O
sets	O
that	O
result	O
in	O
a	O
specific	O
behavior	O
change	O
.	O
</s>
<s>
It	O
is	O
mostly	O
employed	O
for	O
finding	O
the	O
patch	O
that	O
introduced	O
a	O
bug	B-Error_Name
.	O
</s>
<s>
Another	O
application	O
area	O
is	O
finding	O
the	O
patch	O
that	O
indirectly	O
fixed	O
a	O
bug	B-Error_Name
.	O
</s>
<s>
The	O
process	O
of	O
locating	O
the	O
changeset	B-Protocol
that	O
introduced	O
a	O
specific	O
regression	B-Error_Name
was	O
described	O
as	O
"	O
source	B-Protocol
change	I-Protocol
isolation	I-Protocol
"	O
in	O
1997	O
by	O
Brian	O
Ness	O
and	O
Viet	O
Ngo	O
of	O
Cray	O
Research	O
.	O
</s>
<s>
Regression	B-Error_Name
testing	O
was	O
performed	O
on	O
Cray	O
's	O
compilers	B-Language
in	O
editions	O
comprising	O
one	O
or	O
more	O
changesets	B-Protocol
.	O
</s>
<s>
Source	B-Protocol
change	I-Protocol
isolation	I-Protocol
narrowed	O
the	O
cause	O
to	O
a	O
single	O
changeset	B-Protocol
that	O
could	O
then	O
be	O
excluded	O
from	O
editions	O
,	O
unblocking	O
them	O
with	O
respect	O
to	O
this	O
problem	O
,	O
while	O
the	O
author	O
of	O
the	O
change	O
worked	O
on	O
a	O
fix	O
.	O
</s>
<s>
Ness	O
and	O
Ngo	O
outlined	O
linear	B-Algorithm
search	I-Algorithm
and	O
binary	O
search	O
methods	O
of	O
performing	O
this	O
isolation	O
.	O
</s>
<s>
Code	B-Protocol
bisection	I-Protocol
has	O
the	O
goal	O
of	O
minimizing	O
the	O
effort	O
to	O
find	O
a	O
specific	O
change	O
set	O
.	O
</s>
<s>
revision	B-Architecture
control	I-Architecture
in	O
a	O
code	B-General_Concept
repository	I-General_Concept
.	O
</s>
<s>
Code	O
history	O
has	O
the	O
structure	O
of	O
a	O
directed	O
acyclic	O
graph	O
which	O
can	O
be	O
topologically	B-Algorithm
sorted	I-Algorithm
.	O
</s>
<s>
This	O
makes	O
it	O
possible	O
to	O
use	O
a	O
divide	B-Algorithm
and	I-Algorithm
conquer	I-Algorithm
search	O
algorithm	O
which	O
:	O
</s>
<s>
Bisection	B-Protocol
is	O
in	O
LSPACE	O
having	O
an	O
algorithmic	B-General_Concept
complexity	I-General_Concept
of	O
with	O
denoting	O
the	O
number	O
of	O
revisions	O
in	O
the	O
search	O
space	O
,	O
and	O
is	O
similar	O
to	O
a	O
binary	O
search	O
.	O
</s>
<s>
For	O
code	B-Protocol
bisection	I-Protocol
it	O
is	O
desirable	O
that	O
each	O
revision	O
in	O
the	O
search	O
space	O
can	O
be	O
built	O
and	O
tested	O
independently	O
.	O
</s>
<s>
For	O
the	O
bisection	B-Protocol
algorithm	O
to	O
identify	O
a	O
single	O
changeset	B-Protocol
which	O
caused	O
the	O
behavior	O
being	O
tested	O
to	O
change	O
,	O
the	O
behavior	O
must	O
change	O
monotonically	O
across	O
the	O
search	O
space	O
.	O
</s>
<s>
For	O
a	O
Boolean	O
function	O
such	O
as	O
a	O
pass/fail	O
test	O
,	O
this	O
means	O
that	O
it	O
only	O
changes	O
once	O
across	O
all	O
changesets	B-Protocol
between	O
the	O
start	O
and	O
end	O
of	O
the	O
search	O
space	O
.	O
</s>
<s>
If	O
there	O
are	O
multiple	O
changesets	B-Protocol
across	O
the	O
search	O
space	O
where	O
the	O
behavior	O
being	O
tested	O
changes	O
between	O
false	O
and	O
true	O
,	O
then	O
the	O
bisection	B-Protocol
algorithm	O
will	O
find	O
one	O
of	O
them	O
,	O
but	O
it	O
will	O
not	O
necessarily	O
be	O
the	O
root	O
cause	O
of	O
the	O
change	O
in	O
behavior	O
between	O
the	O
start	O
and	O
the	O
end	O
of	O
the	O
search	O
space	O
.	O
</s>
<s>
The	O
root	O
cause	O
could	O
be	O
a	O
different	O
changeset	B-Protocol
,	O
or	O
a	O
combination	O
of	O
two	O
or	O
more	O
changesets	B-Protocol
across	O
the	O
search	O
space	O
.	O
</s>
<s>
To	O
help	O
deal	O
with	O
this	O
problem	O
,	O
automated	O
tools	O
allow	O
specific	O
changesets	B-Protocol
to	O
be	O
ignored	O
during	O
a	O
bisection	B-Protocol
search	O
.	O
</s>
<s>
Although	O
the	O
bisection	B-Protocol
method	O
can	O
be	O
completed	O
manually	O
,	O
one	O
of	O
its	O
main	O
advantages	O
is	O
that	O
it	O
can	O
be	O
easily	O
automated	O
.	O
</s>
<s>
It	O
can	O
thus	O
fit	O
into	O
existing	O
test	B-Application
automation	I-Application
processes	O
:	O
failures	O
in	O
exhaustive	O
automated	O
regression	B-Error_Name
tests	O
can	O
trigger	O
automated	O
bisection	B-Protocol
to	O
localize	O
faults	O
.	O
</s>
<s>
Ness	O
and	O
Ngo	O
focused	O
on	O
its	O
potential	O
in	O
Cray	O
's	O
continuous	O
delivery-style	O
environment	O
in	O
which	O
the	O
automatically	O
isolated	O
bad	O
changeset	B-Protocol
could	O
be	O
automatically	O
excluded	O
from	O
builds	O
.	O
</s>
<s>
The	O
revision	B-Architecture
control	I-Architecture
systems	I-Architecture
Fossil	B-Protocol
,	O
Git	B-Application
and	O
Mercurial	B-Protocol
have	O
built-in	O
functionality	O
for	O
code	B-Protocol
bisection	I-Protocol
.	O
</s>
<s>
The	O
user	O
can	O
start	O
a	O
bisection	B-Protocol
session	O
with	O
a	O
specified	O
range	O
of	O
revisions	O
from	O
which	O
the	O
revision	B-Architecture
control	I-Architecture
system	I-Architecture
proposes	O
a	O
revision	O
to	O
test	O
,	O
the	O
user	O
tells	O
the	O
system	O
whether	O
the	O
revision	O
tested	O
as	O
"	O
good	O
"	O
or	O
"	O
bad	O
"	O
,	O
and	O
the	O
process	O
repeats	O
until	O
the	O
specific	O
"	O
bad	O
"	O
revision	O
has	O
been	O
identified	O
.	O
</s>
<s>
Other	O
revision	B-Architecture
control	I-Architecture
systems	I-Architecture
,	O
such	O
as	O
Bazaar	B-Protocol
or	O
Subversion	B-Application
,	O
support	O
bisection	B-Protocol
through	O
plugins	O
or	O
external	O
scripts	O
.	O
</s>
<s>
Phoronix	B-Application
Test	I-Application
Suite	I-Application
can	O
do	O
bisection	B-Protocol
automatically	O
to	O
find	O
performance	O
regressions	O
.	O
</s>
