<s>
Distributed	B-Operating_System
concurrency	I-Operating_System
control	I-Operating_System
is	O
the	O
concurrency	B-Operating_System
control	I-Operating_System
of	O
a	O
system	O
distributed	B-Architecture
over	O
a	O
computer	B-Architecture
network	I-Architecture
(	O
Bernstein	O
et	O
al	O
.	O
</s>
<s>
In	O
database	B-Application
systems	I-Application
and	O
transaction	B-General_Concept
processing	I-General_Concept
(	O
transaction	O
management	O
)	O
distributed	B-Operating_System
concurrency	I-Operating_System
control	I-Operating_System
refers	O
primarily	O
to	O
the	O
concurrency	B-Operating_System
control	I-Operating_System
of	O
a	O
distributed	B-Operating_System
database	I-Operating_System
.	O
</s>
<s>
It	O
also	O
refers	O
to	O
the	O
concurrency	B-Operating_System
control	I-Operating_System
in	O
a	O
multidatabase	O
(	O
and	O
other	O
multi-transactional	O
object	O
)	O
environment	O
(	O
e.g.	O
,	O
federated	B-General_Concept
database	I-General_Concept
,	O
grid	B-Architecture
computing	I-Architecture
,	O
and	O
cloud	B-Architecture
computing	I-Architecture
environments	O
.	O
</s>
<s>
A	O
major	O
goal	O
for	O
distributed	B-Operating_System
concurrency	I-Operating_System
control	I-Operating_System
is	O
distributed	B-Operating_System
serializability	I-Operating_System
(	O
or	O
global	B-Operating_System
serializability	I-Operating_System
for	O
multidatabase	O
systems	O
)	O
.	O
</s>
<s>
Distributed	B-Operating_System
concurrency	I-Operating_System
control	I-Operating_System
poses	O
special	O
challenges	O
beyond	O
centralized	O
one	O
,	O
primarily	O
due	O
to	O
communication	O
and	O
computer	O
latency	O
.	O
</s>
<s>
It	O
often	O
requires	O
special	O
techniques	O
,	O
like	O
distributed	B-Operating_System
lock	I-Operating_System
manager	I-Operating_System
over	O
fast	O
computer	B-Architecture
networks	I-Architecture
with	O
low	O
latency	O
,	O
like	O
switched	B-Architecture
fabric	I-Architecture
(	O
e.g.	O
,	O
InfiniBand	B-Architecture
)	O
.	O
</s>
<s>
Commitment	B-Architecture
ordering	I-Architecture
(	O
or	O
commit	B-Architecture
ordering	I-Architecture
)	O
is	O
a	O
general	O
serializability	B-Operating_System
technique	O
that	O
achieves	O
distributed	B-Operating_System
serializability	I-Operating_System
(	O
and	O
global	B-Operating_System
serializability	I-Operating_System
in	O
particular	O
)	O
effectively	O
on	O
a	O
large	O
scale	O
,	O
without	O
concurrency	B-Operating_System
control	I-Operating_System
information	O
distribution	O
(	O
e.g.	O
,	O
local	O
precedence	O
relations	O
,	O
locks	O
,	O
timestamps	O
,	O
or	O
tickets	O
)	O
,	O
and	O
thus	O
without	O
performance	O
penalties	O
that	O
are	O
typical	O
to	O
other	O
serializability	B-Operating_System
techniques	O
(	O
Raz	O
1992	O
)	O
.	O
</s>
<s>
The	O
most	O
common	O
distributed	B-Operating_System
concurrency	I-Operating_System
control	I-Operating_System
technique	O
is	O
strong	O
strict	O
two-phase	O
locking	O
(	O
SS2PL	O
,	O
also	O
named	O
rigorousness	O
)	O
,	O
which	O
is	O
also	O
a	O
common	O
centralized	O
concurrency	B-Operating_System
control	I-Operating_System
technique	O
.	O
</s>
<s>
SS2PL	O
provides	O
both	O
the	O
serializability	B-Operating_System
,	O
strictness	O
,	O
and	O
commitment	B-Architecture
ordering	I-Architecture
properties	O
.	O
</s>
<s>
Strictness	O
,	O
a	O
special	O
case	O
of	O
recoverability	O
,	O
is	O
utilized	O
for	O
effective	O
recovery	O
from	O
failure	O
,	O
and	O
commitment	B-Architecture
ordering	I-Architecture
allows	O
participating	O
in	O
a	O
general	O
solution	O
for	O
global	B-Operating_System
serializability	I-Operating_System
.	O
</s>
<s>
For	O
large-scale	O
distribution	O
and	O
complex	O
transactions	O
,	O
distributed	B-Architecture
locking	O
's	O
typical	O
heavy	O
performance	O
penalty	O
(	O
due	O
to	O
delays	O
,	O
latency	O
)	O
can	O
be	O
saved	O
by	O
using	O
the	O
atomic	O
commitment	O
protocol	O
,	O
which	O
is	O
needed	O
in	O
a	O
distributed	B-Operating_System
database	I-Operating_System
for	O
(	O
distributed	B-Architecture
)	O
transactions	O
 '	O
atomicity	B-General_Concept
(	O
e.g.	O
,	O
two-phase	B-General_Concept
commit	I-General_Concept
,	O
or	O
a	O
simpler	O
one	O
in	O
a	O
reliable	O
system	O
)	O
,	O
together	O
with	O
some	O
local	O
commitment	B-Architecture
ordering	I-Architecture
variant	O
(	O
e.g.	O
,	O
local	O
SS2PL	O
)	O
instead	O
of	O
distributed	B-Architecture
locking	O
,	O
to	O
achieve	O
global	B-Operating_System
serializability	I-Operating_System
in	O
the	O
entire	O
system	O
.	O
</s>
<s>
All	O
the	O
commitment	B-Architecture
ordering	I-Architecture
theoretical	O
results	O
are	O
applicable	O
whenever	O
atomic	O
commitment	O
is	O
utilized	O
over	O
partitioned	O
,	O
distributed	B-Architecture
recoverable	O
(	O
transactional	O
)	O
data	O
,	O
including	O
automatic	O
distributed	B-Architecture
deadlock	O
resolution	O
.	O
</s>
<s>
Such	O
technique	O
can	O
be	O
utilized	O
also	O
for	O
a	O
large-scale	O
parallel	O
database	O
,	O
where	O
a	O
single	O
large	O
database	O
,	O
residing	O
on	O
many	O
nodes	O
and	O
using	O
a	O
distributed	B-Operating_System
lock	I-Operating_System
manager	I-Operating_System
,	O
is	O
replaced	O
with	O
a	O
(	O
homogeneous	O
)	O
multidatabase	O
,	O
comprising	O
many	O
relatively	O
small	O
databases	B-Application
(	O
loosely	O
defined	O
;	O
any	O
process	O
that	O
supports	O
transactions	O
over	O
partitioned	O
data	O
and	O
participates	O
in	O
atomic	O
commitment	O
complies	O
)	O
,	O
fitting	O
each	O
into	O
a	O
single	O
node	O
,	O
and	O
using	O
commitment	B-Architecture
ordering	I-Architecture
(	O
e.g.	O
,	O
SS2PL	O
,	O
strict	O
CO	O
)	O
together	O
with	O
some	O
appropriate	O
atomic	O
commitment	O
protocol	O
(	O
without	O
using	O
a	O
distributed	B-Operating_System
lock	I-Operating_System
manager	I-Operating_System
)	O
.	O
</s>
