<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
conservative	B-Operating_System
two-phase	I-Operating_System
locking	I-Operating_System
(	O
C2PL	O
)	O
is	O
a	O
locking	O
method	O
used	O
in	O
DBMS	B-General_Concept
and	O
relational	B-Application
databases	I-Application
.	O
</s>
<s>
Conservative	O
2PL	B-Operating_System
prevents	O
deadlocks	B-Operating_System
.	O
</s>
<s>
The	O
difference	O
between	O
2PL	B-Operating_System
and	O
C2PL	O
is	O
that	O
C2PL	O
's	O
transactions	O
obtain	O
all	O
the	O
locks	O
they	O
need	O
before	O
the	O
transactions	O
begin	O
.	O
</s>
<s>
In	O
heavy	O
lock	O
contention	O
,	O
C2PL	O
reduces	O
the	O
time	O
locks	O
are	O
held	O
on	O
average	O
,	O
relative	O
to	O
2PL	B-Operating_System
and	O
Strict	B-Operating_System
2PL	I-Operating_System
,	O
because	O
transactions	O
that	O
hold	O
locks	O
are	O
never	O
blocked	O
.	O
</s>
