Tieu luan LTMNC HT

8/7/2019 Tieu luan LTMNC HT

1/26

Tiu lun Lp trnh mng nng cao

MC LC

LI NI U...................................................................................................................2A.PHN L THUYT......................................................................................................4

I. CC KHI NIM C BN VKIN THC CHUNG V H TIN HOC PHN TN..............................................4I.1. Khi nim.........................................................................................................4I.2. u im v hn ch ca h phn......................................................................4I.3. Vn v tr thng tin.....................................................................................5I.4. Vn h thng nhiu bn sao.........................................................................6

II. S GN B THNG TIN TRONG C S D LIU PHN TN...................6II.1 Cc iu kin gi nh v thc t.....................................................................6II.2 Tc ng v giao dch.......................................................................................7

II.3 Trin khai giao dch tn trng s gn b..........................................................8II.4 Qun l gn b cc giao dch............................................................................9III. CC THUT TON M BO S GN B D LIU

TRONG CC C S D LIU PHN TN......................................................10III.1 Thut ton cung cp.......................................................................................10III.2 Kiu sp xp ng du...................................................................................10

III.2.1 Nguyn l..............................................................................................11III.2.2 Trin khai h s n nh........................................................................11III.2.3. Cc hnh vi ngoi ch bnh thng.................................................11

III.3. Thut ton m bo s gn b yu nh b tun t tun hon.......................11III.3.1 Nguyn l..............................................................................................11III.3.2 Trin khai h s n nh........................................................................12III.3.3. Cc hnh vi ngoi ch bnh thng.................................................12

III.4. Thut ton m bo s gn b mnh............................................................12III.4.1 Nguyn l..............................................................................................12III.4.2 Trin khai h s n nh........................................................................13III.4.3 Cc hnh vi ngoi ch bnh thng..................................................13III.4 4 Phn tn biu hin trng thi v chc nng cung cp............................14

B.PHN BI TP............................................................................................................16

I. T VN.16

I.1 Gii thiu bi ton...16I.2 C s l thuyt gii quyt bi ton....16

II. GII QUYT VN ....19II.1 Cc trng thi khc nhau cn xem st cho mi bn sao.....19II.2 S hot ng ca thut ton......20II.3 nh gi hm ca s lng bn sao, s lng thng ip

cn thit thc hin mt cp nht.21

II.4 X l s c trn mt trm..22C. KT LUN...24

GVHD: PGS.TS L Vn Sn Trang 1


2/26


TI LIU THAM KHO.................................................................................................25



3/26


LI NI U

--- ---

Hin nay, vic nghin cu pht trin cc gii php k thut c s cho ccng dng phn tn t c nhng thnh cng nht nh v th hin trong cccng b mi nht. Tuy nhin, c c mt gii php hu hiu p ng cc yucu t ra ca vic gn b d liu trong mi trng phn tn nh

Internet/Intranet, th i hi phi tip tc nghin cu hon thin cc gii phphin hnh.

Vn gn b d liu trong cc h thng phn tn ni chung v cc hthng thng tin ng k trn mng ni ring nh vic ng k cc tua du lch, mua

bn trong cc giao dch thng mi in t, ng k gi ch trong giao thng vnti, ng k d thi trong cc h thng thng tin o to,... tr thnh mt lnhvc thu ht nhiu s quan tm ca cc nh nghin cu l thuyt ln cc nh sn

xut phn mm nhm tm ra cc gii php hu hiu m bo tnh gn b thng tintrong cc c s d liu truy cp ngu nhin vi s lng truy cp ln.

Vic nghin cu, pht trin cc phng php m bo gn b d liutrong mi trng phn tn n nay c mt s thnh cng ng k. Trcht, phi ni n s tch hp hng lot cc hm vo cc h iu hnh, hqun tr c s d liu, ngn ng lp trnh vi phng thc ring r ca tngh cho php m bo phn c bn ca vic gn b thng tin ni chung trongqu trnh a truy cp thng qua h thng vin thng. Vic trin khai phng

php cho php gn b d liu trong mi trng phn tn trong iu kin ltng (khng c bt k s c no) c p dng v mang li nhng hiuqu nht nh cho cc h thng ng k. Tuy nhin, trong qu trnh trinkhai lp trnh v vn hnh cc h thng ng k, vn gn b d liu trongcc c s d liu khi h thng b s c ang t ra nh l vn quan trngv c ngha sng cn trong vic pht trin ton h ni chung. Vi nhng l

do nn trong phm vi tiu lun ca mnh, ti trnh by c nhng vn sau:

Phn L Thuyt

Trnh by cc khi nim c bn v kin thc chung ca h tin hc phn

tn.

S gn b thng tin trong c s d liu phn tn

Thut ton m bo gn b mnh gia cc CSDL phn tn



4/26


Phn Bi Tp

p dng thut ton Mullery m bo gn b d liu trong cc CSDLphn tn.

Xin chn thnh cm n Thy L Vn Sn v Thy ng Hng V trang

b nhng kin thc v thng tin v mn hc v gii thiu nhng ti liu thit thc

ti c th hon thnh tiu lun ny.

Vi kin thc c hn nn tiu lun ny khng trnh khi nhng sai st. Rt

mong nhn c s gp ca Thy v cc anh ch trong lp.

Hc vin thc hin

Nguyn Cao Ti



5/26


A. LY THUYT

I. CC KHI NIM C BN V KIN THC CHUNG V H TIN HOCPHN TN

I.1 Khi nim

H tin hc phn tn hay ni ngn gn l h phn tn l h thng x l thngtin bao gm nhiu b x l hoc b vi x l nm ti cc v tr khc nhau v clin kt vi nhau thng qua h thng vin thng di s iu hnh thng nht camt h iu hnh.

T nh ngha ny, ngi ta c th xem h phn tn nh l mt tp hp baogm cc b x l hoc b vi x l vi b nh v ng h nhp c lp. iu nyng ngha vi vic cc b x l khng s dng chung b nh v ng h. Nh

vy, mi mt h x l thng tin thnh phn ca h phn tn bao gm mt haynhiu b x l v b nh cc b. H x l thng tin thnh phn phi c thit ksao cho v cu trc, s lng v dung lng c th cho php thc hin mt cchtrn vn cc chc nng m n m nhn.

H phn tn c xy dng nhm mc ch phn tn ho cc qu trnh x lthng tin v thc hin cng vic trn cc trm xa nhau. l nhng c s cn

bn cho vic xy dng cc ng dng ln nh thng mi in t, gio dc in t,th vin in t s, xy dng cc c s d liu tm kim

Ta c th ni h phn tn bao gm 4 thc th nh hnh v.

I.2 u v nhc im ca h phn tn

1) u im

Chia x ti nguyn: Chia x ti nguyn trong h thng phn tn cung cp

mt c ch chia x tp tin v tr xa, x l thng tin trong mt c s

d liu phn tn, in n ti mt v tr xa, s dng nhng thit b xa

thc hin cc thao tc


H thngphnmm

H thngd liu

T p hpphncng

H thngtruyn

thng


6/26


Tng tc tnh ton: H thng phn tn cho php phn chia vic tnh

ton trn nhiu v tr khc nhau tnh ton song song.

An ton: Nu mt v tr trong h thng phn tn b hng, cc v tr khc

vn tip tc lm vic m khng nh hng n ton b h thng.

Thng tin lin lc vi nhau: C nhiu lc, chng trnh cn chuyn i

d liu t v tr ny sang v tr khc. Khi cc v tr c ni kt vi nhau

trong mt h thng mng, vic trao i d liu din ra rt d.

2) Hn ch

Gi pht trin phn mm cao: Do cc kh khn khi ci t mt h thng

phn tn, gi thnh s tng ln.

D mc li hn: V cc trm trong h phn tn lm vic song song, khc th m bo thut ton c thc hin ng trn tt c cc trm. Do

vy m s li s tng ln.

Khi lng cc x l tng: H thng phn tn cn truyn nhiu thng

bo, nhiu tnh ton ph. Do vy khi lng x l tng ln so vi h

thng tp trung.

I.3 Vn tr thng tin

Trong h phn tn, thi hn truyn mt thng ip l hiu s gia thi imnhn v thi im truyn. Ta gi s rng, thi hn ln so snh vi h tptrung, l a lng bin thin v cp my ny khc vi cp my khc. T tac hai h qu sau y:

1) mt thi im cho trc, mt b x l ang thc hin trn mt my chc th bit c trng thi gn ng ca cc my khc.

2) Trt t nhn cc thng ip trn cc my nhn c th khng ging trt tpht ca chnh cc thng ip .

Cc my trn mng c th b s c v cc thng ip c th b mt. Giiphp cho vn ny l my pht nh s th t tt c cc gi thng tin gi i kmtheo cc s cho my nhn. Nu my pht khng nh s th my nhn s khngxc inh c th t cc gi tin. Ta c h qu ba l:

3) Hai my ging nhau cha thng tin hon ton ging nhau li khng baogi ging nhau v mt trng thi.

T nhng vn nu trn, ta rt ra cc c tnh tng qut ca h phn tn:

i) Thi gian truyn thng ip l mt bin vi gi tr khc nhau, gi tr ny

c th rt ln.ii) Tn sut xut hin cc s c trong khi vn hnh mng ln.



7/26


iii) Vic truy cp ti nguyn, kch hot cc tin trnh trong mng khng ththc hin bi mt thit b duy nht, m chc nng ny phi c phn tn trnnhiu my trn mng.

I.4 Vn h thng nhiu bn sao

Trong h phn tn, qu trnh t chc, vn hnh cc h thng cho php ng kt xa, tng h thng cc b u c lu tr mt bn sao ca tt c cc thng tin linquan ang c tt c cc h thng cc b.

u im ni bt ca kiu t chc ny l:

i) D dng thc hin vic truy cp thng tin cn thit cho cc yu cu ngay tih thng cc b ca mnh

ii) Cho kt qu truy cp mt cch nhanh chng.

Tuy nhin, ch cho kt qa tng i chnh xc v ph thuc rt nhiu vo phngphp v thi hn cp nht thng tin trong cc CSDL cc b.

S tn ti nhiu bn sao trong mt h phn tn trn nhiu h thng cc bkhc nhau c th dn n cc h qu sau y:

i) Cp nht thng tin din ra do ng k gn hay t xa hoc s thay i thngtin cc b trn mt h cc b no cn phi c tin hnh cho tt c cc hthng cc b v khng c php b st h thng no c. trong khon thi gianlm ti, thng tin phi m bo sao cho vic truy vn d liu cho kt qu kp thihay t truy vn trong trng thi treo.

ii) Cn phi trnh trng hp cc thao tc trn hai bn sao khc nhau nhngcha cng mt thng tin c truy cp bi hai hay nhiu yu cu dn n khnggn b.

Hai vn va nu trn xc nh v cc rng buc i vi vn gn b dliu. m bo s gn b ny iu kin l phi bt buc tun th trnh t no cho cc bn sao, cc cp nht thng tin.

Bin php hng u nhm thc hin vic loi tr tng h tng qut trn tphp cc bn sao khi ng k v thc hin vic ng k trc khi tr li bnh

thng. Bin php ny c mt hn ch l khng cho php cc chng trnh ngk thc hin song song. Tt c cc bn sao u c kho cht trong lc ng k.

II. S GN B THNG TIN TRONG C S D LIU PHN TNII.1 Cc iu kin gi nh v thc t

Ta c mt tp thng tin no c th c truy cp bi mt tp cc tin trnh.

S lng cc thng tin c th truy cp c v cc tin trnh c nhu cu thng tin

l con s c nh. H ny pht trin ri rc theo thi gian gia cc im quan st,

ta c th nhn bit c trng thi thc ca chng, c ngha l cc i tng v



8/26


ng cnh thc hin cc tin trnh, h kiu nh vy hot ng vi n nh tuyt

vi.

Cc iu kin gi nh ny so vi h thc t c nhng im khc nhau c bn

sau y:STT So snh

1

- Cc i tng v cc tin trnh c th

- c to lp v hu b c tnh cht ng trong sut qu trnh tn

ti ca h.

2

- Cc i tng v cc tin trnh c th c phn tn trn cc trm

khc nhau lin h vi nhau qua h thng vin thng. Do vy, ta

khng th xc nh trng thi thi im ca h v l do tr ng

truyn gia cc trm v tnh khng tng thch gia cc im quan

st trong trm .

3- H thng vin thng v cc tin trnh l cc i tng c th xy ra

s c k thut.

II.2 Tc ng v giao dch

Cc i tng khc nhau ca h khng phi l cc i tng c lp nhau,chng quan h vi nhau bi tp hp cc quan h gi l cc rng buc ton vn.

Cc rng buc ny th hin su sc cc c tnh ring bit ca h.

Trng thi ca h tho mn mt tp cc rng buc ton vn gi l trng thi

gn b.

Cc nh thit k v vn hnh h mong mun rng vic thc hin cc tin trnh

phi duy tr cho c h trong trng thi gn b. chnh xc ho c tnh ny,

cn phi lu l trng thi ca h ch c xc nh mc quan st cho trc.

Ta quan tm n hai mc quan st:

STT Mc Gii thch

1 NSD

- Tin trnh l mt dy thc hin cc giao dch Giaodch l chng trnh duy nht c thc hin t mttrng thi gn b dn h n mt trng thi gn bkhc.

2 H thng - Mi giao dch c cu to t nt dy cc tc ng



9/26


c th hin nh sau. Nu 2 tc ng A v B thuchai giao dch khc nhau c thc hin bi hai tintrnh th hiu ng tng qut ca chng s l hiu ngca dy (A;B) hoc l (B;A)

Cho mt tp hp giao dch M={T1,T2,Tn} ln lt c thc hin bi cctin trnh c lp p1,p2,pn. vic thc hin tun t c ngha l thc hin tt c cc

giao dch ca M theo kiu ni ui nhau v tun th mt trt t no . S gn b

ca h c bo ton.

mc h thng, ta c th ni rng cc tc ng l phn t nh nht khng th

chia ct c na. Nu v l do hiu qu, nhiu giao dch c thc hin song

song th s gn b khng cn m bo c na. Mt yu cu khc na rt quan

trng l trong qu trnh thc hin h phi m bo cho cc tc ng khng bngt qung.

II.3 Trin khai giao dch tn trng s gn b

Cho mt tp hp giao dch M={T1,T2,Tn}. Mt trt t ha ca tp hp cc

tc ng thnh phn s tng ng vi vic thc hin hon ton cc giao dch. Vic

thu c mt trt t ha gn b ch c th thnh cng khi p dng cc rng buc

trn trt t thc hin cc tc ng. Nguyn l ca phng php l ch lm chm

mt tc ng no cho n thi im m s thc hin ca n khng cn c nguyc ph hy s gn b ca trt t ha.

m bo cc giao dch trn tn trng s gn b thng tin th ngi ta a

ra cc phng php, c ch m bo khi giao dch vn c s gn b thng tin

ton vn d liu trn c s d liu phn tn l:

C ch then ci.

Then ci loi tr tng h. Then ci la chn i tng.

Giao dch hai pha.

By gi ta tng tng rng cc i tng c phn tn trn nhiu trm

khc nhau v c ni vi nhau thng qua h thng vin thng v cc tin trnh

din ra trn cc trm khc nhau. H thng vin thng cho php cc tin trnh trn

cc trm khc nhau c th trao i cc thng ip vi nhau. Ta gi nh rng cc



10/26


tin trnh v cc phng tin truyn thng l cc i tng c th ri vo s c.

Mt h qun l tp hp thng tin phn tn bao gm:

STT C ch

1 - C ch cho php sp xp mt cch tng qut cc tcng ca cng mt giao dch, ngay c khi cc tc ngny din ra trn cc trm khc nhau.

2- C ch iu khin cc tranh chp truy cp cc b vocc i tng m bo tn trng tnh ton vn ca cci tng truy cp cc b ny.

3- C ch c kh nng x l cc b tc v thiu thn vhn, hu qu ca vic hy b cc giao dch.

4 - C ch phc hi cc giao dch hy b hay x l ccs c.

C ch x l s c

STT Phi thc hin

1 Giao dch T bt buc phi thc hin mt cch trn vn

2 Nu c s c xy ra th phi quay li im xut pht.

Mun thc hin nhng iu va nu trn, ngi ta i hi giao dch phi

c cc c tnh ton vn nh sau:

STT Phi thc hin

1

- Nu mt tin trnh b s c trc khi kt thc T nhng

li sau cc thao tc thay i cn thit ca T, trng thi

ca h l gn b.

2- Nu mt tin trnh b s c trc khi din ra cc thay

i ca T, trng thi ca h l gn b.

3- Nu mt tin trnh b s c gia cc thay i ca T,

trng thi ca h l khng gn b.

Nu d liu c phn tn trn nhiu server, bo m d liu s c ghi

ln ng n ln mi c s d liu, i hi phi c cc c ch bo v d liu. V

d nh vic c p nht bng cn i ti khon khch hng ba c s d liu khc

nhau. Nu c s c kt ni xy ra trong thi gian ghi giao dch, c s d liu s

mt tnh ng b. X l giao dch khc phc tnh trng ny bng cch gim st



11/26


nhng thay i tc ng ln cc c s d liu lin quan nhm bo m ton vn d

liu mt khi c s c.

II.4 Qun l gn b cc giao dch

By gi ta hy xem xt mt h, trong cc i tng c phn tn trn

nhiu trm, khng c bn sao mi i tng ch tn ti c mt bn duy nht. Mt

giao dch Tj c th tham chiu n cc i tng nm trn cc trm khc nhau v

do vy gm nhiu tc ng thc hin trn nhiu trm. Nh vy ta phi xc nh

trn mt trm Si mt tin trnh Pji vi nhim v thc hin cc tc ng giao dch Tj

trn Si, cc tc ng c thc hin trn cc trm khc nhau c th tin hnh theo

kiu song song.

Cc phng php qun l gn b cc giao dch nh: Phng php d phng chng b tc, phng php da vo vic hn ch cc kh nng din ra bng cch

pht hin b tc c tnh cht ng, iu dn n hy b cc giao dch.

III. CC THUT TON M BO S GN B D LIU TRONG CC

C S D LIU PHN TN

III.1 Thut ton cung cp:

V s n nh v hiu qu m ta phi phn tn chc nng cung cp trn nhiutrm khc nhau. S hot ng gng b vi nhau gia cc chng trnh cung cp lrt cn thit bo m cho hot ng cung cp c hon ton chnh xc.

Mt s hot ng gn b d liu ca cc chng trnh cung cp phn tn qunl trn cng mt tp hp cc ti nguyn ch t c nu tun th cc nguyn tcsau:

i) Cc b cung cp bt buc phi thc hin cng mt gii thut

ii) Cc b cung cp u nhn tt c cc thng ip pht i t cc tin trnh

iii) Cc thng ip phi c x l cng mt trt t nh nhau trong ccchng trnh cung cp. Trt t duy nht trn tp hp cc thng ip ca h, v trtt c thc hin thng qua vit hp lc gia cc tin trnh cung cp hay tin trnh

pht thng ip

III.2 Sp xp kiu ng du

Trm pht c gn mt gi tr gi l du. Gi tr ny c tnh cht thi imcho trm pht thng tin v da vo ng h Logc cc b ca chnh trm.

III.2.1 Nguyn l:



12/26


Tp hp tt c cc yu cu cp nht c sp xp theo cng mt kiu trntt c cc trm nh c ch du. Theo mi mt yu cu c pht i cho tp hpcc trm, trn mi trm tn ti mt tin trnh server m nhn nhim v tip nhncc yu cu theo mt trt t v du. iu cho php c mt s gn b yu giacc bn sao.

III.2.2. Trin khi h s n nh:

Cc giao dch cn xt y l cc kh nng c, ghi hay cp nht. Cp nhtc xc nh nh mt dy cc thao tc c ri ghi, thao tc kim tra - c tc thtrng thi hin hnh ca bn sao.

Mi mt server tip nhn cc yu cu ghi n cc trm cc b thi imcho trc. n tip nhn cc yu cu v tnh ton trn c s du theo tiu ch lunht. iu dn n chng ta cn phi ch hai trng hp:

Trng hp 1: Tp hp cc yu cu ghi khi ch cha cc yu cu t tt ccc trm khc. Trong trng hp ny cc yu cu i qua, nu chng tn ti, l mihn so vi cc yu cu i qua. Ni cch khc, yu cu lu nht chnh l yu cuang ch.

Trng hp 2: Tn ti cc trm m khng c bt k yu cu no ctruyn n. Ta gii quyt bng cch truyn cho tt c cc trm mt thng ip yucu v bt buc phi xc nhn. Do vy, sau mt khong thi gian theo gi thit v n nh ta s xc nhn: hoc l cc yu cu i qua, hoc l tr li cc thng ipyu cu. Lc ny, ta ni c cc thng ip n t tt c cc trm.

III.2.3. Cc hnh vi bn ngoi ch bnh thng:C hai vn m rng hn i vi thut ton ny l cho php rt ra hay chn

vo tu mt trm no . iu , dn n hai vn sau chng ta cn phi tntrng:

Vn 1: Vic t nhin bin mt mt trm no pah c cc trm khcnhn bit mt cch t ng.

Vn 2: Vic pht i mt thng ip l php ton khng th chia ct ic na. l mt thng ip hoc l tt c cc trm u phi nhn c hoc l

khng mt trm no nhn c c.V vy, nu iu kin u tin c khng ch th iu kin th hai mi c

m bo.

III.3. Thut ton m bo s gn b yu nh b tun t tun hon:

III.3.1. Nguyn l:Trc khi pht mt yu cu mt trm no cn phi kt hp vi n mt s

th t c cp t b tun t tun hon. Cc yu cu c tip nhn ti m trm

theo cng mt trt t thng nht. iu gip ta c c mt s gn b yu. iu



13/26


chng ta cn quan tm y l c ch phn phi cc s da trn nn tng t chccc trm theo kiu vng trn o.

III.3.2. Trin khai h s n nh:B tun t cung cp cho mi yu cu s sp ti cn cha dng, gi s d l

T. Khi n phin ca trm nhn b tun t, n yu cu mt s lng n s ngbng s lng cc yu cu cp nht ang ch trn trm ny. Cc s ny l:

T, T + 1, T + 2, .T + n 1N tip tc chuyn b tun t cho trm k tip lin sau n v s sp ti cha

dng n T + n.Khi mt trm c s c, n pht yu cu cp nht cng vi s ny. Trn

mi trm, cc cp nht c thc hin bng cch tip nhn cc yu cu cng ccs lin tip nhau( theo mt trt t). xc nh yu cu sp n cn phi x l ,mi mt trm duy tr mt bin s V c phi hp vi yu cu x l cui cng.Cc yu cu mang cc s ln hn V + 1 c lu tr trong khi ch x l yu cu

V + 1.III.3.3. Cc hnh vi ngoi ch bnh thng:Hin ti. ngi ta ch to thnh cng v a vo s dng mt cch n

nh trong mng mt s giao thc cho php ti sinh b tun t khi b ny b mtv t cu hnh vng trn o tr li theo kiu t ng.

Cc giao thc hot ng trong iu kin gi nh l mng vin thng chophp pht hin cc s c ca mt trm v cn phi c b khuyt mt cch y nhm duy tr trt t ton phn cn thit cho vic gn b:

Vn 1: Vic ti sinh b tun t cn phi tin hnh song song vi vic tnh

ton s sp c dng.Vn 2: Khi pht hin c mt trm b s c, ta cn phi xc nh cc s mtrm ny ly v cc s cn cha s dng, ri gi cc yu cu c mang cc sny

Vn 3: Vic cho mt trm hi nhp vo li trong vng trn cn phi tinhnh song song vi vic cp nht li cc bn sao ca n.

S dng cc s lin tc cho php trnh c hin tng mt vi cp nht bmt v cc ln mt m khng c pht hin. Vic trin khai b tun t tun honcng lm cho ta gp phi mt s kh khn khc.

III.3.4. Thut ton m bo s gn b mnh:

III.3.4.1. Nguyn l:

Tp hp bao gm cc trm c t chc theo kiu vng trn o. cc cpnht c thc hin theo hai th:

1. Thng nht gia cc trm.

2. Thc hin cp nht.

Do vy, thut ton ny m bo s gn b mnh. Nu c nhiu yu cu cpnht din ra ng thi th ta phi c quy tc quyt nh yu cu no c tip



14/26


nhn v tha mn. Nhm phc v cho tng , ta thng hay s dng du phihp cho mi cp nht v ta x l yu cu c thi gian lu nht.

III.3.4.2. Trin khai h s n nh:

Trng thi c th cu mi trm l:

STT Trng thi Gii thch

1 Ngh ngi Trm khng thc hin cp nht no c

2 Hot ng Trm nhn mt yu cu cp nht cc b m yu cuny c truyn cho trm khc kim tra.

3 Th ng Trm ng cho mt cp nht v ch trt t tngng.

4 Cp nht Trng ang trong tnh trng chuyn ca cp nht ,trong khi tt c cc yu cu khc truyn n uc lu tr. Chng s c x l khi quay v mttrong cc trng thi khc.

Lc khi s, tt c cc trm u trong trng thi ngh ngi.

Trm khi s vic cp nht , u tin cn phi gi mt yu cu cho php cpnht, n ch lm c vic trong trng thi ngh ngi. Lc ny n c nhn

du v c gi vo vng trn trm khi s chuyn t trng thi ngh ngi sangtrng thi hot ng.

Nu ch c mt yu cu duy nht c a vo vng trn, n i qua tt ccc trm chuyn cc trm t ngh ngi sang th ng. khi , n tr v ni khis th vic thng nht coi nh hon tt. vic cp nht ni ring lc ny c gi iv mi trm sau khi thc hin tr v trng thi ngh ngi.

Nu c nhiu yu cu a ra ng thi trong vng trn, th tnh hnh ddng din ra xung t. lc ny, ta phi chn mt yu cu c thi gian du lu nht. tin hnh cng vic , ta nu bt vai tr ca b chn ng cho cc trm khi

s. Mt trm no trong trng thi ngh ngi hay th ng phi chuyn ton byu cu n n, mt trm trong trng thi hot ng ch phi chuyn cc yucu c thi gian lu hn cc yu cu m chnh n pht i, cc yu cu khc u bdng li v c lu tr.

Cc yu cu b lu tr li s c gi tip vo vng trn, khi trm lu trchng hon thnh cng vic cp nht ring ca mnh.

III.3.4.3. Hnh vi ngoi ch bnh thng:

Cc giao thc t li cu hnh vng trn theo kiu t ng c s dng

nhm rt ra hay cho vo ty mt s trm nht nh. Cc s c k thut l rt kh



15/26


khn pht hin cc chin lc m d cc yu cu khng c ghi li khp nitrong mng.

III.4 Phn tn biu hin trng thi v chc nng cung cp

Phn tn biu hin trng thi v chc nng cung cp, c cc gii php c th:

i) Duy tr ti mi trm mt bn sao trng thi ti nguyn tng qut

ii) Phn tn biu hin trang thi trn cc trm, mi mt trm ch c trng thicc ti nguyn cc b ca mnh. Cc quyt nh c a ra trn cc trm khcnhau cn phi c phi hp theo kiu sao cho d liu ca vic cung cp phic gn b vi nhau

iii) Nhm sp xp nhm bo m cho tt c cc yu cu ti nguyn xut phtt cc tin trnh n c cc b cung cp khc nhau theo mt trt t duy nhtc c nh t trc.

Ni dung ca cc bn sao trn cc trm ca h c th phn nh nh sau:

- Tp hp tt c cc ti nguyn cn cha c cung cp- Tp hp cc ti nguyn cung cp- i tng ang chim gi ti nguyn- Kiu s dng- Tp hp cc yu cu khng c tha mn- Tp hp cc thng ip dnh cho trng hp c s dng- Tp hp cc thng ip dnh cho trng hp tht bi

Ngy nay, trong cc ng dng ln nh thng mi in t, gio dc in t,,bn sao d liu c s dng tng tnh sn sng ca d liu. Tuy nhin, li chsn sng ca d liu ny ch c c khi phi tr gi bng nhng thut ton phctp n i tnh phc tp trong vic bo tr nhiu bn sao ca i tng. S khkhn nm vic phi m bo gn b cho cc bn sao ca i tng trnh btc khi vn hnh h thng.

Cc thut ton gii quyt nhng vn ny c gi l cc thut ton iu khinbn sao.

Vic qun l nhiu bn sao ca cng mt i tng thng tin ang c ccnh chuyn mn tin hc quan tm nghin cu ngay trong giai on phn tch, thitk v xy dng h iu hnh. Ngoi ra, y cn l mt trong nhng vn c tnhcht c s cho cc ng dng phc tp.

Qun l nhiu bn sao l gii php k thut bao gm tp hp cc thng tin cnhn bn t mt i tng thng tin v cc chng trnh qun l chng trong mitrng phn tn.

Vn truy cp v x l thng tin phn tn ni chung, qun l nhiu bn saoni ring c nghin cu trong hng lot cc cng trnh ca Herman, Ellis,

Wilms v Le Lann.



16/26


Ni dung qun l nhiu bn sao l cc gii php cho php t ng ha cc cngvic:

Kim tra tnh hp l ca vic truy cp thng tinKhi phc thng tinCp nht thng tinAn ton d liu cho cc bn saoS dng cc b nh, aChuyn cc bn loi b vo vng c th khi phc

Trong cc ni dung nu trn, vn quan trng nht l cp nht t ng thngtin vo cc bn sao./.



17/26


B. BI TP

I. T VN

I.1 Gii thiu bi tonTrong mt h thng phn tn gi nh c n nh tuyt vi, ta mun duy tr

mt s gn b mnh gia cc bn sao ca mt i tng c nh v trn cc

trm khc nhau.

Thut ton da trn cc nguyn l sau y:

Trc khi thc hin cp nht, mt trm no cn phi yu cu v

thng nht vi cc trm khc. Khi c c s thng nht, th trm ny tin hnh cng vic cp

nht; iu ny phi tin hnh trn tt c cc bn sao; i tng khng th

truy cp chng no cc bn sao cn cha cp nht ht.

Cc xung t gia cc trm c gii quyt bng mt trt t c h s

u tin gia cc trm, c c nh mt ln lc khi s cho ton b.

1.

Hi c bao nhiu trng thi khc nhau cn xem xt cho mi bn sao.2. Hy trnh by s hot ng ca thut ton ( th pht trin).

3. Hy nh gi bng hm ca s lng bn sao, s lng cc thng ip cn

thit thc hin mt thng ip.

4. Ta phi sa i thut ton nh th no chu ng c s c trn mt

trm (gi s h vin thng hot ng tt).

I.2 C s l thuyt gii quyt bi tonKhi nghin cu v h phn tn chng ta thy rng, thi gian truy cp trung

bnh vo thng tin trong h phn tn c th c rt ngn, trong mt s trng

hp, nh vo phng php nhn nhiu bn v c gi l nhiu bn sao ca mt

i tng thng tin.

Ta cn phn bit hai trng hp khc nhau c th hin sau y:

- Trng hp 1:



18/26


a) a x l vi b nh chung:

Hnh 6.a x l vi b nh chung

Mi mt b x l u c b nh cc b ca mnh, hay cn gi l cache, c

dng sao chp li cc vng ang lm vic ca b nh chung. Mt chng trnh

th hin thut ton thay th m nhn nhim v lm mi cc b nh cc b.

Trng hp c nhiu b x l mun truy cp vo cng mt i tng, ta s dng

nh l s tham chiu n phin bn ca i tng tm thy trong b nh chung.

b) H truy cp t xa thng qua mt my server duy nht:


L

Bch

BcbBcb

LB x l

B nh cc b

B nh chung

(e)

(e)

B x l

B nh cc b(e)

B nh chung(e)

L

Bch

BcbBcb

L B x l

B nh cc b

B nh chung

(e)

(e)L

My client

My server

B x l

B nh cc b (e)

B nh chung (e)

H thng vin thng

My client

My server


19/26


Hnh 7. H truy cp t xa thng qua my server

Trong trng hp ny, mt i tng c a vo trn mt trm xc nh v

c qun l bi mt server cc b trn trm ny. Khi mt tin trnh xa mun sdng i tng, n phi bt u bng yu cu server cho mt bn sao thng qua h

thng vin thng. Sau khi s dng xong, tin trnh phi gi li cho server mt

phin bn c sa i ca i tng.

Cc trng hp th hin trong hnh 2.1 v 2.2 xt theo chc nng l ging

nhau. l trng hp mt bn duy nht ca i tng l mt c quyn.

- Trng hp 2:Tnh cn i gia cc ngi s dng ti nguyn thng tin ca mng.

Hnh 8. H thng i xng

Ti y, tt c cc bn ng vai tr i xng. Cng vic c tin hnh theo

kiu ny cho php rt ngn thi gian truy cp, nu s ln truy cp c ln hn


L

ee

L

e

L

e

LL

e

L

e

. . . . . .

. . . . . .

H thng vin thng


20/26


s ln truy cp cp nht v v l do thun li s dng theo ngha c sn dng.

Tnh hnh nu trn t ra cho chng ta nhiu vn cn phi gii quyt.

chnh l cc ln cp nht thng tin hay ni mt cch tng qut l cp nht cc bn

sao. T , ta rt ra cc c im quan trng sau y :1) Khi ch tn ti mt bn tp trung c quyn, ta c th t ra rng vic thay

i i tng thc hin trn mt trong cc bn sao s c sao li ngay lp tc vo

bn chnh. chnh l trng hp ghi tc thi v cc cp nhp u gn b. Vi

cc phng php ghi khc, ngc li, cc thay i tng ng ca mt bn sao i

tng cc b ch c sao li trn bn chnh khi thut ton thay th c thc hin

nhm cung cp li cc bn ghi b chim bi bn sao cc b .2) Khi khng tn ti bn c quyn, ta c th gp cc trng hp khng gn

b thng tin.

Trng hp th hai lm pht sinh hai yu cu mi:

a. Ton b giao dch thay i bn sao ca i tng cn phi chp li cng

sm cng tt thay i trn tt c cc bn sao khc. Trong khi thc hin giao

dch, khng c bt k sao chp no khc c thc hin. Sau khi thc hin xong,

tt c cc bn sao hon ton ging nhau.

b. Vic cp nht tc thi (theo h tp trung) ca tt c cc bn sao l khng

cn thit.

Trong tt c cc trng hp, mt giao dch tham chiu trng thi mt i

tng thc hin xut pht t mt trm trn bn cc b cn phi cung cp:

- Hoc l mt gi tr cp nht ca tt c cc thay i din ra trc tham chiu.

- Hoc l mt gi tr c, nhng li l gi tr c cp nht thi im

trc .

S tham chiu khng bao gi phi cung cp mt gi tr xut pht t vic thc

hin tng phn ca mt giao dch.

II. GII QUYT VN

II.1 Cc trng thi khc nhau cn xem xt cho mi bn sao

Cc trng thi c th xy ra trn mi bn sao nh sau:



21/26


Stt Trng thi Gii thch

1 Ngh ngi Trm khng thc hin cp nht no c

2 Hot ng Trm nhn mt yu cu cp nht cc b m yu cu ny

c truyn cho cc trm khc kim tra3 Th ng Trm ng cho mt cp nht v ch trt t tng ng

4 Cp nht Trm ang trong tnh trng chuyn ca cp nht, trong khi

tt c cc yu cu khc truyn n u c lu tr. Chng

s c x l khi quay v mt trong cc trng thi khc.

II.2 S hot ng ca thut ton

Cc trm c t chc theo kiu vng trn o. Trc khi thc hin cp nht,

mt trm no cn phi yu cu v thng nht vi cc trm khc. Sau khi c

c s thng nht, th trm ny tin hnh cng vic cp nht.

S hot ng ca thut ton:

Hnh 10. S hot ng ca thut ton

Lc khi s, tt c cc trm u trong trng thi ngh ngi.

Trm khi s vic cp nht, u tin cn phi gi mt yu cu cho php cp

nht, n ch lm c vic trong trng thi ngh ngi. Lc ny n c nhn

du v c gi vo vng trn trm khi s chuyn t trng thi ngh ngi sang

trng thi hot ng.


1

Ngh

ngi

2

Nghngi

3

Nghn

gi

4

Ng

hngi

Yu cu

La chn yu cu c thi gian du dinht nu c nhiu yu cu c a ra

Ngh ngi

Hot ng

Th ng

Cp nht


22/26


Nu ch c mt yu cu duy nht c a vo vng trn, n i qua tt c cc

trm chuyn cc trm t ngh ngi sang th ng. khi , n tr v ni khi s

th vic thng nht coi nh hon tt. vic cp nht ni ring lc ny c gi i v

mi trm sau khi thc hin tr v trng thi ngh ngi.Nu c nhiu yu cu a ra ng thi trong vng trn, th tnh hnh d

dng din ra xung t. lc ny, ta phi chn mt yu cu c thi gian du lu nht.

tin hnh cng vic , ta nu bt vai tr ca b chn ng cho cc trm khi

s. Mt trm no trong trng thi ngh ngi hay th ng phi chuyn ton b

yu cu n n, mt trm trong trng thi hot ng ch phi chuyn cc yu

cu c thi gian lu hn cc yu cu m chnh n pht i, cc yu cu khc u bdng li v c lu tr.

Cc yu cu b lu tr li s c gi tip vo vng trn, khi trm lu tr

chng hon thnh cng vic cp nht ring ca mnh.

Hnh vi ngoi ch bnh thng:Cc giao thc t li cu hnh vng trn

theo kiu t ng c s dng nhm rt ra hay cho vo ty mt s trm nht

nh. Cc s c k thut l rt kh khn pht hin cc chin lc m d cc yu

cu khng c ghi li khp ni trong mng.

II.3 nh gi hm s lng cc bn sao, s lng thng ip cn thit thc

hin mt cp nht

S m t c cu t chc ca h thng nhiu bn sao v vic cp nht cc

bn sao c th hin trong hnh 12 sau y:


t1 t2 tq

b1m

b12

b11

b21 b22 b2m

H thng vin thngS1

S2

Sn

bn1

bn2

bnm

...

...

... ...

Hnh 11. S m t h thng nhiu bn

sao


23/26


bij vi i = 1..n, j = 1..m,trong i ch server, j ch bn sao, n l s lng server c mc ni trong

mng, m l s lng cc i tng d liu

tk vi k = 1..q, trong k l trm, q l s trm c mc ni

Cc rng buc trn cc bn sao:

Trn bn sao ca mt i tng:

Nu ta c n bn sao b1, b2,, bn ca i tng b, mt trong cc rng bucton vn l:

b1 = b2 = ... = bn

Trn cc bn sao ca ton b cc i tng:

b11= b21 =... = bn1

b12 = b22 = ... = bn2

...

b1m = b2m = ... = bnm

Gi M l cc i ca cc cp nht c th din ra ng thi, th M c th tnh

theo cng thc M = n x m.

II.4 X l s c trn mt trm

Nu d liu c phn tn trn nhiu server, bo m d liu s c ghi

ln ng n ln mi c s d liu, i hi phi c cc c ch bo v d liu. Vd nh vic c p nht bng cn i ti khon khch hng ba c s d liu khc

nhau. Nu c s c kt ni xy ra trong thi gian ghi giao dch, c s d liu s

mt tnh ng b. X l giao dch khc phc tnh trng ny bng cch gim st

nhng thay i tc ng ln cc c s d liu lin quan nhm bo m ton vn d

liu mt khi c s c.

Nu mt tin trnh p b s c trong lc thc hin mt giao dch T th trng thi

ca h xut pht t vic thc hin tng phn chc chc s khng cn gn b.



24/26


Mt c ch cho php duy tr gn b trong mi trng phn tn c s c phi

l:

1) Giao dch T bt buc phi c thc hin mt cch trn vn

2) Nu c s c din ra th bt buc n phi quay tr li im xut pht.Mun th i hi giao dch phi c c tnh ton vn nh sau:

- Nu mt tin trnh b s c trc khi kt thc T nhng li sau cc thao tc

thay i cn thit ca T, trng thi ca h l gn b

Hnh 12.Ba giai on ca mt giao dch

- Nu mt tin trnh b s c trc khi din ra cc thay i ca T, trng thi

ca h l gn b.

- Nu mt tin trnh b s c gia cc thay i T, trng thi ca h l khng

gn b.

Cc m hnh v gii thut nghin cu phi m bo cc c tnh ton vn d

liu ca h v tun th theo cc giai on th hin trong hnh v 12.

Cn c vo ni dung thng tin cn phi m bo s gn b m ta c th chn

cc thut ton nhm m bo tnh ton vn d liu.


Sau khi cpnht(thay i)

Trc khi cpnht(thay i)

Gn b

Khng Gn b

1

2

3


25/26


C. KT LUN

Trong qu trnh xy dng cc phn mm cho h phn tn h tr cc ng dng

ln nh thng mi in t, chnh ph in t,... vn cp nht thng tin dngchung trong cc bn sao ca cng mt i tng l mt trong nhng vn quan

trng. N khng ch m bo h thng hot ng vi tc bnh qun chp nhn

c, n nh, tin cy m quan trng hn c l phi m bo tnh gn b ca d

liu trong cc bn sao.

M hnh h thng qun l nhiu bn sao ging nhau trn mi trng phn tn

v cc gii thut c nghin cu p ng cc yu cu ca mt h thng phctp vi lng thng tin ln cn phi x l v th hin cc mt sau y:

T ng ha cp nht cc bn sao

Pht trin gii thut nhiu bn sao trong mi trng phn tn hin i

Lm phong ph kh nng ng dng cc tc t di ng.

Trin khai k thut nh du bn iu khin trong qun l nhiu bn sao

B sung l thuyt cp nht nhiu bn sao

Bi tiu lun th hin c ng bng nhng s gii thut v m hnh.



26/26


TI LIU THAM KHO

1. H phn tn TS. L Vn Sn, Nh xut bn i hc quc gia TP. H ChMinh.

2. Nguyn l cc h c s d liu Sch dch Jeffery Ullman Nh xut bnthng k.

3. Distributed Systems (Concepts and Design) George Coulouris, JeanDollimore & Tim Kindberg.

4. http://hoclieumo.com/course/info.php?id=68

5. Tng kt cc cng c xy dng HPT:

http://itp.hut.edu.vn/bkel/course/info.php?id=84

6. Distributed systems engineering: http://www.iop.org/EJ/journal/DSE

7. Introduction for distributed systems: http://code.google.com/edu/parallel/dsd-

tutorial.html

8. Thut ton wait-die system: http://data.uta.edu/~ramesh/cse5306/DC2.html

9. Nhng example v distributed systems: http://portal.acm.org/citation.cfm?

doid=320251.320260
http://hoclieumo.com/course/info.php?id=68http://itp.hut.edu.vn/bkel/course/info.php?id=84http://www.iop.org/EJ/journal/DSEhttp://code.google.com/edu/parallel/dsd-tutorial.htmlhttp://code.google.com/edu/parallel/dsd-tutorial.htmlhttp://data.uta.edu/~ramesh/cse5306/DC2.htmlhttp://portal.acm.org/citation.cfm?doid=320251.320260http://portal.acm.org/citation.cfm?doid=320251.320260http://hoclieumo.com/course/info.php?id=68http://itp.hut.edu.vn/bkel/course/info.php?id=84http://www.iop.org/EJ/journal/DSEhttp://code.google.com/edu/parallel/dsd-tutorial.htmlhttp://code.google.com/edu/parallel/dsd-tutorial.htmlhttp://data.uta.edu/~ramesh/cse5306/DC2.htmlhttp://portal.acm.org/citation.cfm?doid=320251.320260http://portal.acm.org/citation.cfm?doid=320251.320260

Tieu luan LTMNC HT

Documents