<s>
Checkpointing	B-General_Concept
is	O
a	O
technique	O
that	O
provides	O
fault	B-General_Concept
tolerance	I-General_Concept
for	O
computing	O
systems	O
.	O
</s>
<s>
It	O
basically	O
consists	O
of	O
saving	O
a	O
snapshot	B-Application
of	O
the	O
application	B-Application
's	O
state	O
,	O
so	O
that	O
applications	O
can	O
restart	O
from	O
that	O
point	O
in	O
case	O
of	O
failure	O
.	O
</s>
<s>
In	O
the	O
distributed	B-Architecture
computing	I-Architecture
environment	O
,	O
checkpointing	B-General_Concept
is	O
a	O
technique	O
that	O
helps	O
tolerate	O
failures	O
that	O
otherwise	O
would	O
force	O
long-running	O
application	B-Application
to	O
restart	O
from	O
the	O
beginning	O
.	O
</s>
<s>
The	O
most	O
basic	O
way	O
to	O
implement	O
checkpointing	B-General_Concept
,	O
is	O
to	O
stop	O
the	O
application	B-Application
,	O
copy	O
all	O
the	O
required	O
data	O
from	O
the	O
memory	O
to	O
reliable	O
storage	O
(	O
e.g.	O
,	O
parallel	B-Application
file	I-Application
system	I-Application
)	O
and	O
then	O
continue	O
with	O
the	O
execution	O
.	O
</s>
<s>
In	O
case	O
of	O
failure	O
,	O
when	O
the	O
application	B-Application
restarts	O
,	O
it	O
does	O
not	O
need	O
to	O
start	O
from	O
scratch	O
.	O
</s>
<s>
While	O
there	O
is	O
ongoing	O
debate	O
on	O
whether	O
checkpointing	B-General_Concept
is	O
the	O
dominating	O
I/O	O
workload	O
on	O
distributed	B-Architecture
computing	I-Architecture
systems	O
,	O
there	O
is	O
general	O
consensus	O
that	O
checkpointing	B-General_Concept
is	O
one	O
of	O
the	O
major	O
I/O	O
workloads	O
.	O
</s>
<s>
There	O
are	O
two	O
main	O
approaches	O
for	O
checkpointing	B-General_Concept
in	O
the	O
distributed	B-Architecture
computing	I-Architecture
systems	O
:	O
coordinated	O
checkpointing	B-General_Concept
and	O
uncoordinated	O
checkpointing	B-General_Concept
.	O
</s>
<s>
In	O
the	O
coordinated	O
checkpointing	B-General_Concept
approach	O
,	O
processes	O
must	O
ensure	O
that	O
their	O
checkpoints	O
are	O
consistent	O
.	O
</s>
<s>
This	O
is	O
usually	O
achieved	O
by	O
some	O
kind	O
of	O
two-phase	B-General_Concept
commit	I-General_Concept
protocol	I-General_Concept
algorithm	O
.	O
</s>
<s>
In	O
the	O
uncoordinated	O
checkpointing	B-General_Concept
,	O
each	O
process	O
checkpoints	O
its	O
own	O
state	O
independently	O
.	O
</s>
<s>
One	O
of	O
the	O
original	O
and	O
now	O
most	O
common	O
means	O
of	O
application	B-General_Concept
checkpointing	I-General_Concept
was	O
a	O
"	O
save	O
state	O
"	O
feature	O
in	O
interactive	O
applications	O
,	O
in	O
which	O
the	O
user	O
of	O
the	O
application	B-Application
could	O
save	O
the	O
state	O
of	O
all	O
variables	O
and	O
other	O
data	O
to	O
a	O
storage	O
medium	O
at	O
the	O
time	O
they	O
were	O
using	O
it	O
and	O
either	O
continue	O
working	O
,	O
or	O
exit	O
the	O
application	B-Application
and	O
at	O
a	O
later	O
time	O
,	O
restart	O
the	O
application	B-Application
and	O
restore	O
the	O
saved	O
state	O
.	O
</s>
<s>
This	O
was	O
implemented	O
through	O
a	O
"	O
save	O
"	O
command	O
or	O
menu	O
option	O
in	O
the	O
application	B-Application
.	O
</s>
<s>
In	O
many	O
cases	O
it	O
became	O
standard	O
practice	O
to	O
ask	O
the	O
user	O
if	O
they	O
had	O
unsaved	O
work	O
when	O
exiting	O
the	O
application	B-Application
if	O
they	O
wanted	O
to	O
save	O
their	O
work	O
before	O
doing	O
so	O
.	O
</s>
<s>
As	O
batch	O
applications	O
began	O
to	O
handle	O
tens	O
to	O
hundreds	O
of	O
thousands	O
of	O
transactions	O
,	O
where	O
each	O
transaction	O
might	O
process	O
one	O
record	O
from	O
one	O
file	O
against	O
several	O
different	O
files	O
,	O
the	O
need	O
for	O
the	O
application	B-Application
to	O
be	O
restartable	O
at	O
some	O
point	O
without	O
the	O
need	O
to	O
rerun	O
the	O
entire	O
job	O
from	O
scratch	O
became	O
imperative	O
.	O
</s>
<s>
Thus	O
the	O
"	O
checkpoint/restart	O
"	O
capability	O
was	O
born	O
,	O
in	O
which	O
after	O
a	O
number	O
of	O
transactions	O
had	O
been	O
processed	O
,	O
a	O
"	O
snapshot	B-Application
"	O
or	O
"	O
checkpoint	O
"	O
of	O
the	O
state	O
of	O
the	O
application	B-Application
could	O
be	O
taken	O
.	O
</s>
<s>
If	O
the	O
application	B-Application
failed	O
before	O
the	O
next	O
checkpoint	O
,	O
it	O
could	O
be	O
restarted	O
by	O
giving	O
it	O
the	O
checkpoint	O
information	O
and	O
the	O
last	O
place	O
in	O
the	O
transaction	O
file	O
where	O
a	O
transaction	O
had	O
successfully	O
completed	O
.	O
</s>
<s>
The	O
application	B-Application
could	O
then	O
restart	O
at	O
that	O
point	O
.	O
</s>
<s>
Checkpointing	B-General_Concept
tends	O
to	O
be	O
expensive	O
,	O
so	O
it	O
was	O
generally	O
not	O
done	O
with	O
every	O
record	O
,	O
but	O
at	O
some	O
reasonable	O
compromise	O
between	O
the	O
cost	O
of	O
a	O
checkpoint	O
vs.	O
the	O
value	O
of	O
the	O
computer	O
time	O
needed	O
to	O
reprocess	O
a	O
batch	O
of	O
records	O
.	O
</s>
<s>
Thus	O
the	O
number	O
of	O
records	O
processed	O
for	O
each	O
checkpoint	O
might	O
range	O
from	O
25	O
to	O
200	O
,	O
depending	O
on	O
cost	O
factors	O
,	O
the	O
relative	O
complexity	O
of	O
the	O
application	B-Application
and	O
the	O
resources	O
needed	O
to	O
successfully	O
restart	O
the	O
application	B-Application
.	O
</s>
<s>
FTI	O
provides	O
application-level	O
checkpointing	B-General_Concept
that	O
allows	O
users	O
to	O
select	O
which	O
data	O
needs	O
to	O
be	O
protected	O
,	O
in	O
order	O
to	O
improve	O
efficiency	O
and	O
avoid	O
space	O
,	O
time	O
and	O
energy	O
waste	O
.	O
</s>
<s>
If	O
desired	O
,	O
users	O
can	O
dedicate	O
one	O
process	O
per	O
node	O
to	O
overlap	O
fault	B-General_Concept
tolerance	I-General_Concept
workload	O
and	O
scientific	O
computation	O
,	O
so	O
that	O
post-checkpoint	O
tasks	O
are	O
executed	O
asynchronously	O
.	O
</s>
<s>
Their	O
goal	O
is	O
to	O
provide	O
a	O
robust	O
,	O
production	O
quality	O
implementation	O
that	O
checkpoints	O
a	O
wide	O
range	O
of	O
applications	O
,	O
without	O
requiring	O
changes	O
to	O
be	O
made	O
to	O
application	B-Application
code	O
.	O
</s>
<s>
BLCR	O
focuses	O
on	O
checkpointing	B-General_Concept
parallel	O
applications	O
that	O
communicate	O
through	O
MPI	O
,	O
and	O
on	O
compatibility	O
with	O
the	O
software	O
suite	O
produced	O
by	O
the	O
SciDAC	O
Scalable	O
Systems	O
Software	O
ISIC	O
.	O
</s>
<s>
DMTCP	O
(	O
Distributed	O
MultiThreaded	O
Checkpointing	B-General_Concept
)	O
is	O
a	O
tool	O
for	O
transparently	O
checkpointing	B-General_Concept
the	O
state	O
of	O
an	O
arbitrary	O
group	O
of	O
programs	O
spread	O
across	O
many	O
machines	O
and	O
connected	O
by	O
sockets	O
.	O
</s>
<s>
Among	O
the	O
applications	O
supported	O
by	O
DMTCP	O
are	O
Open	B-Library
MPI	I-Library
,	O
Python	B-Language
,	O
Perl	B-Language
,	O
and	O
many	O
programming	O
languages	O
and	O
shell	O
scripting	O
languages	O
.	O
</s>
<s>
Among	O
the	O
Linux	O
features	O
supported	O
by	O
DMTCP	O
are	O
open	O
file	B-Application
descriptors	I-Application
,	O
pipes	O
,	O
sockets	O
,	O
signal	O
handlers	O
,	O
process	O
id	O
and	O
thread	O
id	O
virtualization	O
(	O
ensure	O
old	O
pids	O
and	O
tids	O
continue	O
to	O
work	O
upon	O
restart	O
)	O
,	O
ptys	O
,	O
fifos	O
,	O
process	O
group	O
ids	O
,	O
session	O
ids	O
,	O
terminal	O
attributes	O
,	O
and	O
mmap/mprotect	O
(	O
including	O
mmap-based	O
shared	O
memory	O
)	O
.	O
</s>
<s>
Some	O
recent	O
protocols	O
perform	O
collaborative	O
checkpointing	B-General_Concept
by	O
storing	O
fragments	O
of	O
the	O
checkpoint	O
in	O
nearby	O
nodes	O
.	O
</s>
<s>
This	O
is	O
helpful	O
because	O
it	O
avoids	O
the	O
cost	O
of	O
storing	O
to	O
a	O
parallel	B-Application
file	I-Application
system	I-Application
(	O
which	O
often	O
becomes	O
a	O
bottleneck	O
for	O
large-scale	O
systems	O
)	O
and	O
it	O
uses	O
storage	O
that	O
is	O
closer	O
.	O
</s>
<s>
Docker	B-Language
and	O
the	O
underlying	O
technology	O
contain	O
a	O
checkpoint	O
and	O
restore	O
mechanism	O
.	O
</s>
<s>
CRIU	B-Application
is	O
a	O
user	O
space	O
checkpoint	O
library	O
.	O
</s>
<s>
It	O
was	O
designed	O
for	O
batteryless	O
embedded	O
devices	O
such	O
as	O
RFID	B-Application
tags	I-Application
and	O
smart	O
cards	O
which	O
rely	O
on	O
harvesting	O
energy	O
from	O
ambient	O
background	O
sources	O
.	O
</s>
<s>
If	O
checkpointing	B-General_Concept
,	O
data	O
will	O
be	O
stored	O
in	O
a	O
non-volatile	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
When	O
the	O
energy	O
becomes	O
sufficient	O
for	O
reboot	B-Device
,	O
the	O
data	O
is	O
retrieved	O
from	O
non-volatile	B-General_Concept
memory	I-General_Concept
and	O
the	O
program	O
continues	O
from	O
the	O
stored	O
state	O
.	O
</s>
<s>
Mementos	O
has	O
been	O
implemented	O
on	O
the	O
MSP430	B-Architecture
family	O
of	O
microcontrollers	B-Architecture
.	O
</s>
<s>
Idetic	O
is	O
a	O
set	O
of	O
automatic	O
tools	O
which	O
helps	O
application-specific	O
integrated	O
circuit	O
(	O
ASIC	O
)	O
developers	O
to	O
automatically	O
embed	O
checkpoints	O
in	O
their	O
designs	O
.	O
</s>
<s>
It	O
targets	O
high-level	B-General_Concept
synthesis	I-General_Concept
tools	O
and	O
adds	O
the	O
checkpoints	O
at	O
the	O
register-transfer	O
level	O
(	O
Verilog	B-Language
code	O
)	O
.	O
</s>
<s>
It	O
uses	O
a	O
dynamic	B-Algorithm
programming	I-Algorithm
approach	O
to	O
locate	O
low	O
overhead	O
points	O
in	O
the	O
state	B-Architecture
machine	I-Architecture
of	O
the	O
design	O
.	O
</s>
<s>
Since	O
the	O
checkpointing	B-General_Concept
in	O
hardware	O
level	O
involves	O
sending	O
the	O
data	O
of	O
dependent	O
registers	O
to	O
a	O
non-volatile	B-General_Concept
memory	I-General_Concept
,	O
the	O
optimum	O
points	O
are	O
required	O
to	O
have	O
minimum	O
number	O
of	O
registers	O
to	O
store	O
.	O
</s>
<s>
Idetic	O
is	O
deployed	O
and	O
evaluated	O
on	O
energy	O
harvesting	O
RFID	B-Application
tag	I-Application
device	O
.	O
</s>
