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Transcript of mo and Rodrigues 1 Distributed Systems Foundationshauser/CS564/lectures/2004-08-26.pdf · mo and...
Cpt
S 4
64/5
64 F
all 2
004
Dis
trib
uted
Sys
tem
s F
ound
atio
ns:
© 2
001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 11
Distr
ibut
ed S
yst
ems
Fou
ndation
sP
rof.
Car
l Hau
ser
Cpt
. S 4
64/5
64 L
ectu
reC
hapt
er 1
from
Tex
tA
ugus
t 26
& 3
1 20
04
Cpt
S 4
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004
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trib
uted
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tem
s F
ound
atio
ns:
© 2
001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 22
Hou
sekeeping
Ite
ms
Intr
oduc
tions
–N
ame,
cla
ss (
juni
or, s
enio
r, g
rad,
etc
.), e
mpl
oym
ent
(cur
rent
or
form
er)
•R
oll c
all
Cpt
S 4
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004
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trib
uted
Sys
tem
s F
ound
atio
ns:
© 2
001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 33
Age
nda
•In
trod
uce
som
e te
rms
and
the
big
pict
ure
–W
hat i
s a
dist
ribut
ed s
yste
m?
–W
hen
are
DS
war
rant
ed?
–H
ow d
id D
S e
volv
e?–
Wha
t are
som
e ar
chite
ctur
es fo
r D
S?
•R
evie
w s
ome
conc
epts
from
oth
er c
ours
es a
long
the
way
•P
urpo
se: p
rovi
de th
e fo
unda
tion
for
the
inqu
iry a
nd
inve
stig
atio
n th
at g
oes
on th
roug
hout
this
cla
ss
Cpt
S 4
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004
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trib
uted
Sys
tem
s F
ound
atio
ns:
© 2
001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 44
What
is a
Distr
ibut
ed S
yst
em? (1.1
)•
Man
y di
ffere
nt k
inds
of D
S,
so o
ne d
efin
ition
is n
ot
adeq
uate
!•
Muc
h ea
sier
to ta
lk a
bout
ch
arac
teris
tics/
attr
ibut
es•
Pre
senc
e of
a n
etw
ork
is
nece
ssar
y•
DS
has
mor
e th
an ju
st a
ne
twor
k: s
et o
f dis
trib
uted
p
roto
cols
to a
ssis
t the
di
strib
uted
app
licat
ions
and
se
rvic
es–
Wha
t is
a pr
otoc
ol?
“An
agre
emen
t tha
t spe
cifie
s th
e fo
rmat
[, ti
min
g] a
nd m
eani
ng
of m
essa
ges
[that
] com
pute
rs
exch
ange
” [C
omer
2001
]–
Wha
t tim
e is
it p
roto
col?
Hi?
Yea
h, it
’s 4
:45
You
’re
wel
com
e
Hi
Got
the
time?
Tha
nks
Cpt
S 4
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64 F
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004
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trib
uted
Sys
tem
s F
ound
atio
ns:
© 2
001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 55
DS A
ttribut
es
(con
t.)
•D
S h
as p
roce
sses
that
coo
pera
te to
ach
ieve
som
e co
mm
on g
oal
•Is
the
Inte
rnet
a d
istr
ibut
ed s
yste
m: m
any
com
pute
rs
act a
lone
or
inte
ract
onl
y tr
ivia
lly–
No:
Inte
rnet
con
tain
s pr
otoc
ols
and
serv
ices
that
are
ne
eded
for
build
ing
DS
s, b
ut is
not
, its
elf,
a D
S; a
ttach
ing
a co
mpu
ter
to th
e In
tern
et d
oes
not a
utom
atic
ally
mak
e it
part
of a
dis
trib
uted
sys
tem
–Y
es: t
he In
tern
et c
onta
ins
proc
esse
s su
ch a
s ro
uter
s an
d na
me
serv
ers
that
use
dis
trib
uted
pro
toco
ls to
ach
ieve
a
com
mon
pur
pose
(al
beit
a lo
w-le
vel o
ne)
Cpt
S 4
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004
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trib
uted
Sys
tem
s F
ound
atio
ns:
© 2
001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 66
DS A
ttribut
es
(con
t.)
•S
choe
der’s
defin
ition
of a
DS
–M
ultip
le c
ompu
ters
–In
terc
onne
cted
by
a ne
twor
k–
Sha
ring
som
e st
ate
•W
hat i
s st
ate?
•S
harin
g ac
com
plis
hed
acro
ss ti
me
and
spac
e
•La
mpo
rt’s
defin
ition
–A
DS
is th
e on
e th
at p
reve
nts
you
from
wor
king
be
caus
e of
the
failu
re o
f a m
achi
ne th
at y
ou n
ever
he
ard
of
Cpt
S 4
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004
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trib
uted
Sys
tem
s F
ound
atio
ns:
© 2
001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 77
DS A
ttribut
es
(con
t.)
•T
anen
baum
and
van
Ste
en’s
def
initi
on–
A c
olle
ctio
n of
inde
pend
ent c
ompu
ters
that
app
ears
to it
s us
ers
as a
sin
gle
cohe
rent
sys
tem
Cpt
S 4
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004
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trib
uted
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tem
s F
ound
atio
ns:
© 2
001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 88
DS A
ttribut
es
(con
t.):
•C
ompu
ters
/CP
Us
fail
inde
pend
ently
•C
omm
unic
atio
n –
Is u
nrel
iabl
e–
Unr
elia
ble
how
?–
Has
mod
erat
e la
tenc
y–
Wha
t is
late
ncy?
Wha
t is
mod
erat
e?–
Has
var
iabl
e la
tenc
y–
Has
mod
erat
e ba
ndw
idth
–W
hat i
s ba
ndw
idth
? W
hat i
s m
oder
ate?
•H
ard
to d
eter
min
e th
e re
lativ
e or
derin
g of
eve
nts
–C
lock
s no
t syn
chro
nize
d pe
rfec
tly -
exam
ple
–C
omm
unic
atio
n la
tenc
y–
Res
ult:
only
par
tial o
rder
ing
on e
vent
s is
kno
wn
•V
ery
hard
to a
sses
s th
e gl
obal
sta
te a
t any
one
tim
e–
Mes
sage
s ca
n be
in tr
ansi
t–
Clo
cks
are
not s
ynch
roni
zed
perf
ectly
Cpt
S 4
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004
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trib
uted
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tem
s F
ound
atio
ns:
© 2
001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 99
Tra
nspare
ncy?
•H
ide
diffe
renc
es in
dat
a re
pres
enta
tion
(Acc
ess
Tra
nspa
renc
y)•
Hid
e w
here
a r
esou
rce
is lo
cate
d (L
ocat
ion
T.)
•H
ide
that
a r
esou
rce
may
mov
e (M
igra
tion
T.)
•H
ide
that
a r
esou
rce
may
mov
e w
hile
in u
se
(Rel
ocat
ion
T.)
•H
ide
that
a r
esou
rce
is r
eplic
ated
(R
eloc
atio
n T
.)•
Hid
e th
at a
res
ourc
e is
sha
red
(Con
curr
ency
T.)
•H
ide
failu
re a
nd r
ecov
ery
of a
res
ourc
e (F
ailu
re T
.)•
Hid
e w
heth
er a
res
ourc
e is
in m
emor
y or
on
disk
(P
ersi
sten
ce T
.)
Cpt
S 4
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004
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trib
uted
Sys
tem
s F
ound
atio
ns:
© 2
001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 1
010
How
muc
h t
rans
pare
ncy is
pos
sible?
•Lo
catio
n –
dist
ance
mat
ters
•F
ailu
re –
can
affe
ct ti
me
take
n•
Rep
licat
ion
–ca
n af
fect
tim
e ta
ken
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004
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trib
uted
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tem
s F
ound
atio
ns:
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001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 1
111
Cent
ralized v
s. D
istr
ibut
ed S
ys.
Sec
urity
-pe
rmea
ting
Sec
urity
-bo
unda
ry
Gra
cefu
l deg
rada
tion/
Par
tial f
ailu
reA
ll or
non
e
Sha
ring
Con
sist
ency
Sca
labi
lity
Mod
ular
ityM
anag
eabi
lity
Het
erog
enei
tyH
omog
enei
ty
Geo
grap
hic
scop
e/re
sour
ces
Loca
l sco
pe a
nd
reso
urce
s
Dis
trib
ute
d S
yste
ms
Cen
tral
ized
Sys
tem
s
Cpt
S 4
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all 2
004
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trib
uted
Sys
tem
s F
ound
atio
ns:
© 2
001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 1
212
When
to D
istr
ibut
e?
•If
you
don’
t nee
d a
DS
, the
n do
n’t d
istr
ibut
e!!!
•B
e ab
le to
ans
wer
“W
hy d
o w
e ne
ed a
dis
trib
uted
sy
stem
to s
olve
this
pro
blem
?”•
Mai
n re
ason
s: d
istr
ibut
e w
hen
1.P
robl
em h
as a
dec
entr
aliz
ed n
atur
e2.
Dis
trib
utio
n te
chni
ques
pro
vide
use
ful s
ervi
ces
even
if
prob
lem
isn’
t nat
ural
ly d
ecen
tral
ized
3.P
robl
em r
equi
res
adap
ting
to c
hang
es a
nd e
volu
tion
in
the
activ
ity a
nd lo
catio
n of
org
aniz
atio
ns
Cpt
S 4
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all 2
004
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trib
uted
Sys
tem
s F
ound
atio
ns:
© 2
001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 1
313
When
to D
istr
ibut
e? (co
nt.)
•#1
: Pro
blem
has
a d
ecen
tral
ized
nat
ure
•M
any
loca
tions
col
labo
ratin
g on
a p
robl
em (
ex?)
–In
vent
ory/
orde
ring
for
a la
rge
reta
iler
–F
inan
cial
rep
ortin
g–
Dis
trib
uted
ast
rono
my
(coo
rdin
ated
use
of r
adio
te
lesc
opes
)–
Fed
erat
ed c
ompu
tatio
nal r
esou
rces
SE
TI@
hom
e, …
Cpt
S 4
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64 F
all 2
004
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trib
uted
Sys
tem
s F
ound
atio
ns:
© 2
001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 1
414
When
to D
istr
ibut
e (co
nt.)
•#2
: DS
tech
niqu
es c
an p
rovi
de u
sefu
l ser
vice
s–
Som
etim
es n
atur
ally
cen
tral
ized
: e.g
. ban
k da
taba
se–
Som
etim
es c
entr
aliz
ed b
usin
ess
mod
el–
But
eve
n so
, som
etim
es d
istr
ibut
ion
can
help
…
•B
ank
acco
unt d
atab
ase
(DB
) ex
ampl
e–
Nat
ural
ly c
entr
aliz
ed: e
asy
cons
iste
ncy
and
perf
orm
ance
–F
ragm
ent D
B a
mon
g re
gion
s: e
xplo
it lo
calit
y of
ref
eren
ce,
red
uce
rel
ian
ce o
n n
etw
ork
fo
r re
mo
te a
cces
s–
Rep
licat
e ea
ch fr
agm
ent f
or f
ault
to
lera
nce
•N
ow n
eed
DS
tech
niqu
es–
Rou
te r
eque
st to
rig
ht fr
agm
ent
–M
aint
ain
cons
iste
ncy
of fr
agm
ents
as
a w
hole
dat
abas
e–
Mai
ntai
n co
nsis
tenc
y of
eac
h fr
agm
ent’s
rep
licas
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S 4
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uted
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tem
s F
ound
atio
ns:
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001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 1
515
When
to D
istr
ibut
e (co
nt.)
•#3
: Ada
ptab
ility
to q
uick
ly c
hang
ing
busi
ness
sc
enar
io–
Allo
w a
uton
omy
in m
anag
ing
serv
ices
and
res
ourc
es
acro
ss d
omai
ns–
Allo
w in
crem
enta
l and
loca
lly-d
riven
exp
anda
bilit
y–
Muc
h ea
sier
to a
dd a
new
bra
nch
offic
e (c
reat
e an
othe
r re
plic
a, e
tc)
if al
read
y di
strib
uted
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S 4
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trib
uted
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tem
s F
ound
atio
ns:
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001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 1
616
Serv
ices
of D
istr
ibut
ed S
yst
ems
(1.2
)•
DS
sha
ve a
set
of b
asic
ser
vice
s (T
able
1.3
)–
Ofte
n au
gmen
ted
with
oth
er s
peci
fic s
ervi
ces
usef
ul fo
r pa
rtic
ular
app
licat
ions
•N
ame
serv
ice
•R
egis
trat
ion,
Aut
hent
icat
ion,
and
Aut
horiz
atio
n S
ervi
ces
•F
ile S
ervi
ce•
Net
wor
king
Ser
vice
•R
emot
e In
voca
tion
Ser
vice
•B
roke
rage
Ser
vice
(fa
ncy
nam
e se
rvic
e)•
Tim
e S
ervi
ce•
Adm
inis
trat
ion
Ser
vice
s: m
anag
emen
t tas
ks
Cpt
S 4
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004
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trib
uted
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tem
s F
ound
atio
ns:
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001-
2003
Car
l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 1
717
Evo
lution
of
Distr
ibut
ed C
ompu
ting
•E
volv
ing
fast
sin
ce e
arly
197
0s–
Mile
ston
e ev
ent:
AR
PA
NE
T (
BB
N, 1
969)
, firs
t int
erne
t
–N
ot a
lwa
ys c
lear
wha
t sho
uld
and
wou
ld b
e di
strib
uted
(w
hich
re
sour
ces)
: app
s, fi
les,
mem
ory,
pro
cess
ing
–K
ey
enab
lers
: lo
cala
ndw
ide-
area
netw
orki
ng
•F
irst s
tage
–S
harin
g fil
es: f
tp
–R
emot
e ac
cess
to C
PU
s: te
lnet
•F
tp is
a p
ain,
erg
o di
strib
uted
file
sys
tem
s–
Sam
e sy
stem
cal
l (fo
pen)
wor
ks lo
cal a
nd r
emot
e
•D
istr
ibut
ed c
oncu
rren
t pro
cess
ing:
div
ide
and
conq
uer
acro
ss
mac
hine
s•
Rem
ote
exec
utio
n: c
all n
on-lo
cal p
roce
dure
/met
hod
–G
ave
birt
h to
clie
nt-s
erve
r pa
radi
gm–
Rem
ote
proc
edur
e ca
ll: R
PC
…. t
hen
rem
ote
obje
cts
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uted
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tem
s F
ound
atio
ns:
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l Hau
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& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 1
818
Distr
ibut
ed S
yst
em A
rchitect
ures
(1.3
)•
Q: w
hat i
s an
arc
hite
ctur
e?
•A
rchi
tect
ure
vs. f
ram
ewor
k•
DS
arc
hite
ctur
es h
ave
evol
ved
as h
ardw
are
and
softw
are
avai
labl
e be
cam
e m
ore
soph
istic
ated
•P
rese
nted
now
in r
ough
ord
er o
f evo
lutio
n•
Hig
h-le
vel a
rchi
tect
ures
giv
en, m
any
way
s to
im
plem
ent (
we
will
stu
dy s
ome…
.)
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tem
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& D
avid
E. B
akke
n. S
ome
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es ©
200
1 V
eris
sím
o an
d R
odrig
ues 1
919
Remot
e A
ccess
•T
he m
ost b
asic
form
of d
istr
ibut
ion
•G
oal:
prov
ide
dist
ribut
ed a
cces
s to
cen
tral
ized
fa
cilit
ies
(a)
term
inal
acc
ess
over
PO
TS
: mos
t prim
orda
l(b
) re
mot
e se
ssio
ns o
ver
data
net
wor
k: fi
les,
em
ail,
…
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uted
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tem
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ound
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l Hau
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& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 2
020
File a
nd M
emor
y D
istr
ibut
ion
•C
omin
g of
wor
ksta
tions
allo
wed
com
putin
g po
wer
to
be s
prea
d ou
t–
Add
ed u
p to
a lo
t of r
esou
rces
–F
ile a
nd m
emor
y di
strib
utio
n sh
are
on a
pee
r ba
sis
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uted
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tem
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ound
atio
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l Hau
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& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 2
121
Remot
e A
ccess
II
•O
ops:
DS
sno
t so
easy
to a
dmin
iste
r &
sha
re
perf
ectly
….
•B
ackl
ash:
re-
cent
raliz
e so
me
reso
urce
s(a
)D
iskl
ess
wor
ksta
tions
(b)
X-T
erm
inal
s
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trib
uted
Sys
tem
s F
ound
atio
ns:
© 2
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l Hau
ser
& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 2
222
Client
-Serv
er
Arc
hitect
ures
•O
ops:
X-t
erm
inal
s an
d di
skle
ss W
Ss
unsa
tisfa
ctor
y•
Clie
nt-s
erve
r ar
chite
ctur
es: b
reak
up
appl
icat
ion
into
two
rem
ote
piec
es–
Mos
t wid
ely-
depl
oyed
arc
hite
ctur
e to
day
(a)
Clie
nt-S
erve
r A
rchi
tect
ure
(b)
Fat
clie
nts:
clie
nt m
achi
nes
have
cod
e fo
r ea
ch a
pp.
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trib
uted
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tem
s F
ound
atio
ns:
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l Hau
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& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 2
323
3-Tier
Client
-Serv
er
Arc
hitect
ures
•O
ops,
fat c
lient
s a
big
pain
(co
de, f
iles,
con
fig)
•O
ops,
too
muc
h di
strib
utio
n at
ser
ver
leve
l•
Thi
n cl
ient
s: r
educ
ed fu
nctio
nalit
y (b
ut m
ore
than
X
-Ter
min
als)
•3-
Tie
r ar
chite
ctur
e1.
Hum
an-c
lient
inte
rfac
e (G
UI m
achi
ne)
2.A
pplic
atio
n se
rver
3.D
atab
ase
or s
econ
dary
ser
vers
“be
hind
” ap
p se
rver
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tem
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E. B
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n. S
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es ©
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1 V
eris
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o an
d R
odrig
ues 2
424
3-Tier
Client
-Serv
er
Arc
hitect
ures
(con
t.)
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uted
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tem
s F
ound
atio
ns:
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l Hau
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& D
avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 2
525
Mob
ile C
ode a
nd S
ite A
rchitect
ures
•O
ops:
–
thin
clie
nts
too
limite
d–
non-
dedi
cate
d cy
cles
•M
obile
cod
e: s
hip
code
whe
n ne
eded
to c
lient
(a)
Por
tabl
e an
d m
obile
cod
e(b
)M
obile
Site
Arc
hite
ctur
es: c
lient
s an
d se
rver
s ca
n m
ove
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uted
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tem
s F
ound
atio
ns:
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l Hau
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& D
avid
E. B
akke
n. S
ome
figur
es ©
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1 V
eris
sím
o an
d R
odrig
ues 2
626
Mob
ile S
ite A
rchitect
ures
(con
t.)
•Lo
ts o
f pos
sibl
e ap
plic
atio
ns–
mili
tary
–em
erge
ncy
netw
orks
–
•V
aria
tions
–O
nly
allo
w c
lient
to m
ove
(mob
ile c
ell p
hone
net
wor
ks)
–O
nly
allo
w s
ites
to m
ove
whi
le o
fflin
e, th
en r
eapp
ear
(“no
mad
ic c
ompu
ting”
)… v
ery
popu
lar
toda
y, g
row
ing
wild
ly fa
st…
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E. B
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n. S
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es ©
200
1 V
eris
sím
o an
d R
odrig
ues 2
727
Eve
nt-Base
d A
rchitect
ures
•O
ops:
clie
nt-s
erve
r pa
radi
gm d
oes
not r
epre
sent
all
kind
s of
use
ful d
istr
ibut
ed a
pplic
atio
ns•
Som
e ar
e m
ore
peer
-pee
r•
Som
e re
quire
han
dlin
g un
solic
ited
even
ts•
Exa
mpl
e: c
lient
ser
ver
–cl
ient
: ini
tiate
s re
ques
t, ge
ts r
eply
–se
rver
: mai
ntai
ns s
tate
, get
s re
ques
t, se
nds
repl
y ba
sed
on
stat
e
•E
vent
-bas
ed (
AK
A m
essa
ge-b
ased
) ar
chite
ctur
es–
Ser
ver
gene
rally
mai
ntai
ns s
tate
, but
can
initi
ate
even
ts /
mes
sage
s / i
nvoc
atio
ns–
E.g
., w
hen
its s
tate
cro
sses
a th
resh
old
–E
xam
ples
?
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tem
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atio
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avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 2
828
Eve
nt-Base
d A
rchitect
ures
(con
t.)
•E
vent
-bas
ed c
omm
unic
atio
n of
ten
mul
ticas
t/gro
up•
Can
run
mul
tipee
rco
nver
satio
ns: d
irect
ly s
endi
ng
mes
sage
s to
ano
ther
•A
sym
met
ric e
xam
ple:
pro
duce
r-co
nsum
er•
Exa
mpl
e ap
ps: e
mai
l, U
SE
NE
T n
ews
•“P
ush”
tech
nolo
gies
are
pro
duce
r-co
nsum
er•
Enh
ance
men
t: le
t pro
duce
rs a
nd c
onsu
mer
s no
t ha
ve b
e on
line
at s
ame
time:
mes
sage
que
ues
•E
nhan
cem
ent:
let c
onsu
mer
s sp
ecify
(su
bscr
ibe)
on
ly w
hat
(typ
e,va
lue)
of m
essa
ges
they
rec
eive
: “p
ublis
h-su
bscr
ibe”
(A
KA
“m
essa
ge b
us”)
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atio
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E. B
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n. S
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es ©
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1 V
eris
sím
o an
d R
odrig
ues 2
929
Eve
nt-Base
d A
rchitect
ures
(con
t.)
•F
igur
es(a
)M
ultip
eer
(b)
Pub
lish-
subs
crib
e
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tem
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E. B
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ome
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es ©
200
1 V
eris
sím
o an
d R
odrig
ues 3
030
For
mal Not
ions
for
DSs
(1.4
): D
S M
odels
•W
arni
ng: h
eavy
not
atio
n ah
ead
–O
nly
a sm
all p
art o
f the
cla
ss!
•D
Ss
mod
eled
as
set o
f Npr
oces
ses
or p
artic
ipan
ts p
re
sidi
ng o
n M
proc
esso
rs o
r si
tes
deno
ted
s.•
Site
s in
terc
onne
cted
by
som
e ne
twor
k, to
polo
gies
va
ry•
Evo
lutio
n of
a s
yste
m m
odel
ed b
y ev
ents
ei p
–ith
even
t of t
imel
ine
of e
ach
proc
ess
p–
Om
it su
bscr
ipt o
r su
pers
crip
ts w
hen
not a
mbi
guou
s
•W
hen
need
ed: a
ssoc
iate
phy
sica
l tim
esta
mps
with
ev
ents
: t(e
)is
the
real
tim
e in
stan
t whe
n e
took
pla
ce–
Alte
rnat
ely,
t 0, t
a, t b
, …
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n. S
ome
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es ©
200
1 V
eris
sím
o an
d R
odrig
ues 3
131
DS M
odels (co
nt.)
•S
tate
of a
pro
cess
, S, i
s m
odifi
ed u
pon
the
occc
uren
ceof
eac
h ev
ent
•E
volu
tion
of s
tate
of S
is it
s hi
stor
y, H
•H
is a
n or
dere
d se
t of t
uple
s: <
even
t, ev
ent s
tate
>•
A r
unis
an
orde
red
set o
f eve
nts
in a
pro
cess
ex
ecut
ion,
des
crib
ed b
y a
hist
ory
•A
dis
trib
uted
run
is a
par
tially
ord
ered
set
of e
vent
s in
the
exec
utio
n of
sev
eral
pro
cess
es
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es ©
200
1 V
eris
sím
o an
d R
odrig
ues 3
232
Repr
ese
nting
Distr
ibut
ed C
omput
ation
s•
Eve
nts
at a
pro
cess
can
be
–ex
ecut
ion
even
ts: i
nter
nal c
ompu
tatio
ns–
send
eve
nts:
sen
ding
a m
essa
ge to
ano
ther
pro
cess
–re
ceiv
e ev
ents
: rec
eivi
ng a
mes
sage
from
ano
ther
pro
cess
•M
essa
ge e
xcha
nges
dep
icte
d w
ith ti
mel
ines
: e.g
.
p 1 p 2 p 3m
ab
c
de
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avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 3
333
Global Sta
tes
•S
omet
imes
ver
y us
eful
to g
et a
glo
bal “
pict
ure”
of a
di
strib
uted
sys
tem
•G
loba
l sta
te(G
S)
of a
DS
at a
ny p
oint
is a
vec
tor
of
its in
divi
dual
pro
cess
sta
tes:
S =
{S
1, S
2, …
, SM}
•T
wo
view
poin
ts o
f sys
tem
evo
lutio
n:–
Inte
rleav
ing
view
: sys
tem
goe
s th
roug
h a
succ
essi
on o
f st
ates
–S
pace
-tim
e vi
ew: s
yste
m g
oes
thro
ugh
a pa
rtia
lly o
rder
ed
set o
f eve
nts
occu
ring
in s
ever
al p
roce
sses
in th
e sy
stem
•A
cut
(in s
pace
-tim
e vi
ew)
is a
seg
men
t int
erse
ctin
g th
e tim
elin
es o
f all
proc
esse
s.
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n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 3
434
Global Sta
tes
(con
t.)
•S
tron
gly
cons
iste
nt c
ut (
SC
C):
faith
fully
rep
rese
nts
GS
of t
he s
yste
m
p 1 p 2 p 3 p 4
m3
m1
m2
m4
•In
cons
iste
nt c
ut (
IC):
giv
es in
valid
pic
ture
of G
S•
Con
sist
ent c
ut (
CC
): g
ives
val
id b
ut p
ossi
bly
inco
mpl
ete
pict
ure
of th
e G
S o
f the
sys
tem
SC
CIC
CC
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l Hau
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avid
E. B
akke
n. S
ome
figur
es ©
200
1 V
eris
sím
o an
d R
odrig
ues 3
535
DS P
ropert
ies
•G
oal:
spec
ify a
sys
tem
with
hig
h-le
vel p
rope
rtie
s•
Saf
ety
prop
ertie
s : s
omet
hing
bad
(w
rong
eve
nts)
ne
ver
take
s pl
ace
–S
peci
ficat
ion:
pre
dica
te P
will
nev
er b
e tr
ue in
the
DS
•Li
vene
sspr
oper
ties:
som
ethi
ng g
ood
(pos
itive
eve
nt)
even
tual
lyta
kes
plac
e–
Spe
cific
atio
n: p
redi
cate
Pw
ill e
vent
ually
be
true
in th
e D
S
•“a
ny d
eliv
ered
mes
sage
is d
eliv
ered
to a
ll co
rrec
t pa
rtic
ipan
ts”:
saf
ety
prop
erty
•“a
ny m
essa
ge s
ent i
s de
liver
ed to
at l
east
one
pa
rtic
ipan
t”: l
iven
ess
prop
erty
•T
imel
ines
s pr
oper
ties
rela
te th
e tim
es a
t whi
ch
even
ts o
ccur
–e.
g. e
vent
a o
ccur
s <
.1 s
econ
d af
ter
even
t b.