{"id":30878,"date":"2019-10-31T21:37:56","date_gmt":"2019-10-31T18:37:56","guid":{"rendered":"https:\/\/prohoster.info\/blog\/tranzaktsii-i-mehanizmy-ih-kontrolya\/"},"modified":"2019-10-31T21:37:56","modified_gmt":"2019-10-31T18:37:56","slug":"tranzaktsii-i-mehanizmy-ih-kontrolya","status":"publish","type":"post","link":"https:\/\/prohoster.info\/sq\/blog\/administrirovanie\/tranzaktsii-i-mehanizmy-ih-kontrolya","title":{"rendered":"Transaksionet dhe mekanizmat e kontrollit t\u00eb tyre","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Transaksionet<\/h2>\n

<\/p>\n

Transaksioni \u00ebsht\u00eb nj\u00eb sekuenc\u00eb e operacioneve mbi t\u00eb dh\u00ebna q\u00eb ka fillim dhe fund.<\/h4>\n

\nTransaksioni \u00ebsht\u00eb ekzekutimi sequential i operacioneve t\u00eb leximit dhe shkruajtjes. Fundi i nj\u00eb transaksioni mund t\u00eb jet\u00eb ose shp\u00ebtimi i ndryshimeve (konfirmimi, commit) ose anullimi i ndryshimeve (rrezimi, rollback). Nd\u00ebrsa i referohemi bazave t\u00eb t\u00eb dh\u00ebnave, nj\u00eb transaksion p\u00ebrb\u00ebhet nga disa k\u00ebrkesa q\u00eb interpretohen si nj\u00eb k\u00ebrkes\u00eb e vetme.<\/p>\n

Transaksionet duhet t\u00eb p\u00ebrmbushin pronat ACID.<\/h4>\n

\nAto m\u00eb t\u00eb thella. Transaksioni ose realizohet plot\u00ebsisht ose nuk realizohet fare.<\/p>\n

Konsistenca. N\u00eb p\u00ebrfundim t\u00eb transaksionit, kufizimet e vendosura mbi t\u00eb dh\u00ebnat nuk duhet t\u00eb shkelet (p\u00ebr shembull, constraints n\u00eb bazat e t\u00eb dh\u00ebnave). Konsistenca n\u00ebnkupton q\u00eb sistemi do t\u00eb kaloj\u00eb nga nj\u00eb gjendje e sakt\u00eb n\u00eb nj\u00eb tjet\u00ebr gjendje t\u00eb sakt\u00eb.<\/p>\n

Izolimi. Transaksionet q\u00eb ekzekutohen paralelisht nuk duhet t\u00eb ndikojn\u00eb tek nj\u00ebra-tjetra, p\u00ebr shembull, t\u00eb ndryshojn\u00eb t\u00eb dh\u00ebnat q\u00eb p\u00ebrdor nj\u00eb transaksion tjet\u00ebr. Rezultati i ekzekutimit t\u00eb transaksioneve paralel duhet t\u00eb jet\u00eb i till\u00eb si\u00e7 do t\u00eb ishte n\u00ebse transaksionet do t\u00eb ishin ekzekutuar nj\u00ebra pas tjetr\u00ebs.<\/p>\n

Q\u00ebndrueshm\u00ebria. Pas konfirmimit, ndryshimet nuk duhet t\u00eb humbasin.
\n<\/a><\/noindex><\/p>\n

Dita e transaksioneve<\/h2>\n

<\/p>\n

Dita ruan ndryshimet e b\u00ebra nga transaksionet, siguron thell\u00ebsin\u00eb dhe q\u00ebndrueshm\u00ebrin\u00eb e t\u00eb dh\u00ebnave n\u00eb rast t\u00eb nj\u00eb d\u00ebshtimi t\u00eb sistemit.<\/h4>\n

\nDita p\u00ebrmban vlerat q\u00eb t\u00eb dh\u00ebnat kishin para dhe pas ndryshimit nga transaksioni. Strategjia e shkrimit p\u00ebrpara obligon shtimin n\u00eb dit\u00eb t\u00eb sh\u00ebnimeve mbi vlerat e m\u00ebparshme p\u00ebrpara fillimit dhe mbi vlerat p\u00ebrfundimtare pas p\u00ebrfundimit t\u00eb transaksionit. N\u00eb rast t\u00eb ndalimit t\u00eb papritur t\u00eb sistemit, baza e t\u00eb dh\u00ebnave lexon dit\u00ebn n\u00eb rend t\u00eb kund\u00ebrt dhe anullon ndryshimet e b\u00ebra nga transaksionet. Kur has nj\u00eb transaksion t\u00eb nd\u00ebrprer\u00eb, baza e t\u00eb dh\u00ebnave e ekzekuton at\u00eb dhe b\u00ebn ndryshime n\u00eb dit\u00eb. Ndodhur n\u00eb gjendjen n\u00eb momentin e d\u00ebshtimit, baza e t\u00eb dh\u00ebnave lexon dit\u00ebn n\u00eb rend t\u00eb drejtp\u00ebrdrejt\u00eb dhe rikthen ndryshimet e b\u00ebra nga transaksionet. K\u00ebshtu ruhet q\u00ebndrueshm\u00ebria e transaksioneve q\u00eb tashm\u00eb jan\u00eb konfirmuar dhe thell\u00ebsia e transaksionit t\u00eb nd\u00ebrprer\u00eb.<\/p>\n

Thjesht ekzekutimi i p\u00ebrs\u00ebritur i transaksioneve t\u00eb pasakta nuk \u00ebsht\u00eb i mjaftuesh\u00ebm p\u00ebr rikuperimin. <\/p>\n

Shembull. N\u00eb llogarin\u00eb e p\u00ebrdoruesit ka 500$ dhe p\u00ebrdoruesi vendos t\u00eb t\u00ebrheq\u00eb ato p\u00ebrmes bankomati. Kryhen dy transaksione. E para lexon vler\u00ebn e balan\u00ebs dhe n\u00ebse ka mjete t\u00eb mjaftueshme n\u00eb llogari, i jep parat\u00eb p\u00ebrdoruesit. E dyta heq nga bilanci shum\u00ebn p\u00ebrkat\u00ebse. Supozoni se ndodhi nj\u00eb d\u00ebshtim n\u00eb sistem dhe operacioni i par\u00eb nuk u realizua, nd\u00ebrsa i dyti u realizua. N\u00eb k\u00ebt\u00eb rast ne nuk mund t\u00eb japim p\u00ebrs\u00ebri parat\u00eb p\u00ebrdoruesit pa rikthyer sistemin n\u00eb gjendjen e tij fillestare me nj\u00eb bilanc pozitiv.<\/i><\/p>\n

Nivelet e izolimit<\/h2>\n

<\/p>\n

Leximi i t\u00eb dh\u00ebnave t\u00eb fiksuara (Read Committed)<\/h4>\n

\nProblemi i leximit t\u00eb papast\u00ebrt (Dirty Read) q\u00ebndron n\u00eb faktin se transaksioni mund t\u00eb lexoj\u00eb nj\u00eb rezultat t\u00eb p\u00ebrkohsh\u00ebm t\u00eb nj\u00eb transaksioni tjet\u00ebr.<\/p>\n

Shembull. Vlera fillestare e balansit \u00ebsht\u00eb 0$. T1 shton 50$ n\u00eb bilanc. T2 lexon vler\u00ebn e balansit (50$). T1 anullon ndryshimet dhe p\u00ebrfundon. T2 vazhdon ekzekutimin me t\u00eb dh\u00ebna t\u00eb gabuara p\u00ebr bilancin.<\/i><\/p>\n

Zgjidhja \u00ebsht\u00eb leximi i t\u00eb dh\u00ebnave t\u00eb fiksuara (Read Committed) q\u00eb ndalon leximin e t\u00eb dh\u00ebnave t\u00eb modifikuara nga nj\u00eb transaksion. N\u00ebse transaksioni A ndryshon nj\u00eb grup t\u00eb dh\u00ebnash, at\u00ebher\u00eb transaksioni B kur k\u00ebrkon k\u00ebto t\u00eb dh\u00ebna, detyrohet t\u00eb pres\u00eb p\u00ebrfundimin e transaksionit A.<\/p>\n

Leximi i p\u00ebrs\u00ebritur (Repeatable Read)<\/h4>\n

\nProblemi i humbjes s\u00eb ndryshimeve (Lost Updates). T1 ruan ndryshimet mbi ndryshimet e T2.<\/p>\n

Shembull. Vlera fillestare e balansit \u00ebsht\u00eb 0$ dhe dy transaksione e mbushin bilancin nj\u00ebkoh\u00ebsisht. T1 dhe T2 lexojn\u00eb bilancin q\u00eb \u00ebsht\u00eb 0$. M\u00eb pas T2 shton 200$ n\u00eb 0$ dhe ruan rezultatin. T1 shton 100$ n\u00eb 0$ dhe ruan rezultatin. Rezultati p\u00ebrfundimtar \u00ebsht\u00eb 100$ n\u00eb vend t\u00eb 300$.<\/i><\/p>\n

Problemi i leximit t\u00eb pa p\u00ebrs\u00ebritur (Unrepeatable read). Leximi p\u00ebrs\u00ebrit\u00ebs i t\u00eb dh\u00ebnave t\u00eb nj\u00ebjta kthen vlera t\u00eb ndryshme.<\/p>\n

Shembull. T1 lexon vler\u00ebn e balansit q\u00eb \u00ebsht\u00eb 0$. M\u00eb pas T2 shton 50$ n\u00eb bilanc dhe p\u00ebrfundon. T1 p\u00ebrs\u00ebri lexon t\u00eb dh\u00ebnat dhe zbulon nj\u00eb mosmarr\u00ebveshje me rezultatin e m\u00ebparsh\u00ebm.<\/i><\/p>\n

Leximi i p\u00ebrs\u00ebritur (Repeatable Read) garanton q\u00eb leximi p\u00ebrs\u00ebrit\u00ebs do t\u00eb kthej\u00eb t\u00eb nj\u00ebjtin rezultat. T\u00eb dh\u00ebnat e lexuara nga nj\u00eb transaksion nuk mund t\u00eb ndryshojn\u00eb n\u00eb t\u00eb tjerat deri n\u00eb p\u00ebrfundimin e transaksionit. N\u00ebse transaksioni A lexon nj\u00eb grup t\u00eb dh\u00ebnash, at\u00ebher\u00eb transaksioni B kur k\u00ebrkon k\u00ebto t\u00eb dh\u00ebna, detyrohet t\u00eb pres\u00eb p\u00ebrfundimin e transaksionit A.<\/p>\n

Leximi i renditur (Serializable)<\/h4>\n

\nProblemi i leximit fantom (Phantom Reads). Dy k\u00ebrkesa q\u00eb zgjedhin t\u00eb dh\u00ebna sipas nj\u00eb kushti kthejn\u00eb vlera t\u00eb ndryshme.<\/p>\n

Shembull. T1 k\u00ebrkon numrin e t\u00eb gjith\u00eb p\u00ebrdoruesve me nj\u00eb bilanc q\u00eb \u00ebsht\u00eb m\u00eb shum\u00eb se 0$ por m\u00eb pak se 100$. T2 heq 1$ nga p\u00ebrdoruesi me nj\u00eb bilanc prej 101$. T1 ekzekuton p\u00ebrs\u00ebri k\u00ebrkes\u00ebn.<\/i><\/p>\n

Leximi i renditur (Serializable). Transaksionet kryhen si plot\u00ebsisht t\u00eb renditura. Ndalohet t\u00eb p\u00ebrdit\u00ebsohen dhe t\u00eb shtohen t\u00eb dh\u00ebna q\u00eb bien n\u00ebn kushtet e k\u00ebrkes\u00ebs. N\u00ebse transaksioni A ka k\u00ebrkuar t\u00eb dh\u00ebnat e t\u00ebr\u00eb tabel\u00ebs, at\u00ebher\u00eb tabela e t\u00ebr\u00eb bllokohet p\u00ebr transaksionet e tjera deri n\u00eb p\u00ebrfundimin e transaksionit A.<\/p>\n

Planifikuesi (Scheduler)<\/h2>\n

<\/p>\n

P\u00ebrcakton rendin n\u00eb t\u00eb cilin duhet t\u00eb kryhen operacionet gjat\u00eb transaksioneve q\u00eb zhvillohen paralelisht.<\/h4>\n

\nSiguron nj\u00eb nivel t\u00eb caktuar izolimi. N\u00ebse rezultati i ekzekutimit t\u00eb operacioneve nuk varet nga rendi i tyre, at\u00ebher\u00eb k\u00ebto operacione jan\u00eb komutative (Permutable). Operacionet e leximit dhe operacionet mbi t\u00eb dh\u00ebna t\u00eb ndryshme jan\u00eb komutative. Operacionet e leximit-shkrimit dhe shkrimit-shkrimit nuk jan\u00eb komutative. Detyra e planifikuesit \u00ebsht\u00eb t\u00eb nd\u00ebrthuret operacionet q\u00eb kryhen nga transaksionet paralel, n\u00eb m\u00ebnyr\u00eb q\u00eb rezultati t\u00eb jet\u00eb ekuivalent me ekzekutimin sekondar t\u00eb transaksioneve.<\/p>\n

Mekanizmat e kontrollit t\u00eb detyrave paralel (Concurrency Control)<\/h2>\n

<\/p>\n

Optimisti bazohet n\u00eb zbulimin dhe zgjidhjen e konflikteve, pesimisti n\u00eb parandalimin e shfaqjes s\u00eb konflikteve.<\/h4>\n

\nMe qasjen optimiste, disa p\u00ebrdorues marrin kopje t\u00eb t\u00eb dh\u00ebnave. Ai q\u00eb p\u00ebrfundon i pari duke redaktuar ruan ndryshimet, nd\u00ebrsa t\u00eb tjer\u00ebt duhet t\u00eb kryejn\u00eb nj\u00eb bashkim t\u00eb ndryshimeve. Algoritmi optimist lejon q\u00eb konflikti t\u00eb ndodh\u00eb, por sistemi duhet t\u00eb rikuperohet pas konfliktit.<\/p>\n

Me qasjen pesimiste, p\u00ebrdoruesi i par\u00eb q\u00eb kap t\u00eb dh\u00ebnat pengon marrjen e t\u00eb dh\u00ebnave nga t\u00eb tjer\u00ebt. N\u00ebse konflikte jan\u00eb t\u00eb rralla, \u00ebsht\u00eb e arsyeshme t\u00eb zgjidhet strategjia optimiste, pasi ajo siguron nj\u00eb nivel m\u00eb t\u00eb lart\u00eb paralelizmi.<\/p>\n

Bllokimi (Locking)<\/h2>\n

<\/p>\n

N\u00ebse nj\u00eb transaksion ka bllokuar t\u00eb dh\u00ebnat, at\u00ebher\u00eb transaksionet e tjera q\u00eb k\u00ebrkojn\u00eb t\u00eb dh\u00ebna duhet t\u00eb presin t\u00eb zbllokohen.<\/h4>\n

\nNj\u00eb bllokim mund t\u00eb aplikohet mbi nj\u00eb baz\u00eb t\u00eb dh\u00ebnash, tryez\u00eb, rresht ose atribut. Bllokimi i ndar\u00eb (Shared Lock) mund t\u00eb aplikohet mbi t\u00eb dh\u00ebna t\u00eb caktuara nga disa transaksione, duke lejuar leximin nga t\u00eb gjitha transaksionet (p\u00ebrfshir\u00eb at\u00eb q\u00eb e ka vendosur) dhe duke ndaluar ndryshimin dhe bllokimin ekskluziv. Bllokimi ekskluziv (Exclusive Lock) mund t\u00eb aplikohet vet\u00ebm nga nj\u00eb transaksion, duke lejuar \u00e7do veprim t\u00eb transaksionit q\u00eb e ka aplikuar, duke ndaluar veprimet e tjera.<\/p>\n

Nj\u00eb bllokim i nd\u00ebrsjell\u00eb konsiderohet nj\u00eb situat\u00eb kur transaksionet ndodhen n\u00eb nj\u00eb gjendje pritjeje q\u00eb zgjat pafund\u00ebsisht.<\/h4>\n

\nShembuj. Transaksioni i par\u00eb pret lirimin e t\u00eb dh\u00ebnave t\u00eb bllokuara nga i dyti, nd\u00ebrsa i dyti pret lirimin e t\u00eb dh\u00ebnave t\u00eb bllokuara nga i pari.<\/i><\/p>\n

Zgjidhja optimiste e problemit t\u00eb bllokimeve t\u00eb nd\u00ebrsjella lejon q\u00eb bllokimi t\u00eb ndodhi, por m\u00eb pas rikthen sistemin duke anuluar nj\u00eb nga transaksionet e involvuara n\u00eb bllokim.<\/h4>\n

\nMe nj\u00eb periudh\u00eb t\u00eb caktuar kohore, k\u00ebrkohen bllokimet e nd\u00ebrsjella. Nj\u00eb nga metodat e identifikimit \u00ebsht\u00eb p\u00ebrmes koh\u00ebs, q\u00eb do t\u00eb thot\u00eb se supozohet q\u00eb ka ndodhur bllokimi n\u00ebse nj\u00eb transaksion \u00ebsht\u00eb duke u ekzekutuar p\u00ebr nj\u00eb periudh\u00eb shum\u00eb t\u00eb gjat\u00eb. Kur nj\u00eb bllokim i nd\u00ebrsjell\u00eb \u00ebsht\u00eb gjetur, nj\u00eb nga transaksionet anulohet, duke lejuar q\u00eb transaksionet e tjera pjes\u00ebmarr\u00ebse t\u00eb p\u00ebrfundojn\u00eb. Zgjedhja e viktim\u00ebs mund t\u00eb bazohet n\u00eb koston e transaksioneve ose t\u00eb tyre moshuar (skemat Wait-Die dhe Wound-wait). <\/p>\n

\u00c7do transaksion T<\/b> i jepet nj\u00eb mark\u00eb kohore TS<\/b> e cila p\u00ebrmban koh\u00ebn e fillimit t\u00eb ekzekutimit t\u00eb transaksionit.<\/p>\n

Wait-Die. <\/p>\n

N\u00ebse TS(Ti)<\/b> < TS(Tj)<\/b>, at\u00ebher\u00eb Ti<\/b> pret, p\u00ebrndryshe Ti<\/b> anulohet dhe fillon p\u00ebrs\u00ebri me t\u00eb nj\u00ebjt\u00ebn mark\u00eb kohore.<\/u><\/p>\n

N\u00ebse nj\u00eb transaksion m\u00eb i ri ka bllokuar nj\u00eb burim, nd\u00ebrsa nj\u00eb m\u00eb i vjet\u00ebr k\u00ebrkon t\u00eb nj\u00ebjtin burim, at\u00ebher\u00eb transaksionit m\u00eb t\u00eb vjet\u00ebr i lejohet t\u00eb pres\u00eb. N\u00ebse nj\u00eb transaksion m\u00eb i vjet\u00ebr ka bllokuar burimin, at\u00ebher\u00eb transaksioni m\u00eb i ri q\u00eb k\u00ebrkon k\u00ebt\u00eb burim do t\u00eb anulohet.<\/p>\n

Wound-wait. <\/p>\n

N\u00ebse TS(Ti)<\/b> < TS(Tj)<\/b>, at\u00ebher\u00eb Tj<\/b> anulohet dhe fillon p\u00ebrs\u00ebri me t\u00eb nj\u00ebjt\u00ebn mark\u00eb kohore, p\u00ebrndryshe Ti<\/b> pret.<\/u><\/p>\n

N\u00ebse nj\u00eb transaksion m\u00eb i ri ka z\u00ebn\u00eb nj\u00eb burim dhe nj\u00eb transaksion m\u00eb i vjet\u00ebr k\u00ebrkon gjithashtu k\u00ebt\u00eb burim, at\u00ebher\u00eb transaksioni m\u00eb i ri do t\u00eb anulohet. N\u00ebse nj\u00eb transaksion m\u00eb i vjet\u00ebr ka z\u00ebn\u00eb burimin, at\u00ebher\u00eb transaksioni m\u00eb i ri, q\u00eb k\u00ebrkon k\u00ebt\u00eb burim, lejohet t\u00eb pres\u00eb. Zgjedhja e viktim\u00ebs e bazuar n\u00eb mosh\u00ebn parandalon ndodhin e bllokimeve, por anullon transaksionet q\u00eb nuk jan\u00eb n\u00eb gjendje bllokimi. Problemi q\u00ebndron n\u00eb faktin se transaksionet mund t\u00eb anullohen shum\u00eb her\u00eb, pasi nj\u00eb transaksion m\u00eb i vjet\u00ebr mund t\u00eb mbaj\u00eb nj\u00eb burim p\u00ebr nj\u00eb koh\u00eb t\u00eb gjat\u00eb.<\/p>\n

Nj\u00eb zgjidhje pesimiste p\u00ebr problemin e bllokimeve nuk lejon q\u00eb nj\u00eb transaksion t\u00eb filloj\u00eb ekzekutimin n\u00ebse ka rrezik p\u00ebr ndodhin e bllokimit.<\/h4>\n

\nP\u00ebr t\u00eb zbuluar bllokimin, nd\u00ebrtohet nj\u00eb grafik (grafiku i pritjes, wait-for-graph), ku kulmet jan\u00eb transaksionet dhe arkat jan\u00eb t\u00eb orientuara nga transaksionet q\u00eb presin lirimin e t\u00eb dh\u00ebnave drejt transaksioneve q\u00eb kan\u00eb z\u00ebn\u00eb k\u00ebto t\u00eb dh\u00ebna. Kunderth\u00ebnia ndodh n\u00ebse grafiku ka ciklik\u00eb. Nd\u00ebrtimi i grafikut t\u00eb pritjes, sidomos n\u00eb DB t\u00eb shp\u00ebrndara, \u00ebsht\u00eb nj\u00eb procedur\u00eb e shtrenjt\u00eb.<\/p>\n

Bllokimi dyfazor \u2014 parandalimi i bllokimeve p\u00ebrmes kapjes s\u00eb t\u00eb gjith\u00eb burimeve t\u00eb p\u00ebrdorura nga transaksioni n\u00eb fillim t\u00eb transaksionit dhe lirimi i tyre n\u00eb fund.<\/h4>\n

\nT\u00eb gjitha operacionet bllokuese duhet t\u00eb parashikojn\u00eb t\u00eb parin q\u00eb do t\u00eb lirohet. Ka dy faza \u2014 Faza e Rritjes gjat\u00eb s\u00eb cil\u00ebs nd\u00ebrtohen kapjet dhe Faza e Tkurrjes gjat\u00eb s\u00eb cil\u00ebs ndodh lirimi i kapjeve. N\u00eb rast t\u00eb pamund\u00ebsis\u00eb p\u00ebr t\u00eb kapur nj\u00eb nga burimet, transaksioni fillon nga e para. Mund t\u00eb ndodh\u00eb q\u00eb nj\u00eb transaksion t\u00eb mos jet\u00eb n\u00eb gjendje t\u00eb merret me burimet e nevojshme, p\u00ebr shembull n\u00ebse disa transaksione garojn\u00eb p\u00ebr t\u00eb nj\u00ebjtat burime.<\/p>\n

Komitimi dyfazor siguron ekzekutimin e komitit n\u00eb t\u00eb gjitha replikat e DB.<\/h4>\n

\n\u00c7do DB regjistron informacionin p\u00ebr t\u00eb dh\u00ebnat q\u00eb do t\u00eb ndryshohen n\u00eb log dhe i p\u00ebrgjigjet koordinatorit me OK (Faza e Votimit). Pasi t\u00eb gjith\u00eb t\u00eb p\u00ebrgjigjen me OK, koordinator\u00ebt d\u00ebrgojn\u00eb nj\u00eb sinjal q\u00eb detyron t\u00eb gjith\u00eb t\u00eb b\u00ebjn\u00eb komitin. Pas komitit, server<\/a> t\u00eb gjith\u00eb p\u00ebrgjigjen me OK; n\u00ebse ndonj\u00ebra nuk p\u00ebrgjigjet me OK, koordinator\u00ebt d\u00ebrgojn\u00eb nj\u00eb sinjal p\u00ebr t\u00eb anuluar ndryshimet n\u00eb t\u00eb gjitha serverat (Faza e P\u00ebrfundimit).<\/p>\n

Metoda e vulave t\u00eb koh\u00ebs.<\/h2>\n

<\/p>\n

Nj\u00eb transaksion m\u00eb i vjet\u00ebr anullohet kur p\u00ebrpiqet t\u00eb qaset n\u00eb t\u00eb dh\u00ebnat, t\u00eb p\u00ebrfshira nga nj\u00eb transaksion m\u00eb i ri.<\/h4>\n

\n\u00c7do transaksioni i caktohet nj\u00eb timestamp TS<\/b> q\u00eb i p\u00ebrket koh\u00ebs s\u00eb fillimit t\u00eb ekzekutimit. N\u00ebse Ti<\/b> m\u00eb i vjet\u00ebr Tj<\/b>, at\u00ebher\u00eb TS(Ti)<\/b> < TS(Tj)<\/b>.<\/p>\n

Kur transaksioni rikthehet, i caktohet nj\u00eb timestamp i ri. \u00c7do objekt t\u00eb dh\u00ebnash Q<\/b> i angazhuar nga transaksioni sh\u00ebnohet me dy timestamps. W-TS(Q)<\/b> \u2014 timestamp-i i transaksionit m\u00eb t\u00eb ri, q\u00eb ka realizuar nj\u00eb sh\u00ebnim mbi Q<\/b>. R-TS(Q)<\/b> \u2014 timestamp-i i transaksionit m\u00eb t\u00eb ri, q\u00eb ka realizuar nj\u00eb sh\u00ebnim lexim mbi Q<\/b>.<\/p>\n

Kur transaksioni T<\/b> k\u00ebrkon t\u00eb lexoj\u00eb t\u00eb dh\u00ebna Q<\/b> dy skenar\u00eb jan\u00eb t\u00eb mundsh\u00ebm.<\/p>\n

N\u00ebse TS(T)<\/b> < W-TS(Q)<\/b>, pra n\u00ebse t\u00eb dh\u00ebnat jan\u00eb p\u00ebrdit\u00ebsuar nga nj\u00eb transaksion m\u00eb i ri, at\u00ebher\u00eb transaksioni T<\/b> rikthehet.<\/u><\/p>\n

N\u00ebse TS(T)<\/b> >= W-TS(Q)<\/b>, at\u00ebher\u00eb leximi kryhet dhe R-TS(Q)<\/b> kthehet n\u00eb MAX(R-TS(Q), TS(T))<\/b>.<\/u><\/p>\n

Kur transaksioni T<\/b> k\u00ebrkon t\u00eb ndryshoj\u00eb t\u00eb dh\u00ebnat Q<\/b> dy skenar\u00eb jan\u00eb t\u00eb mundsh\u00ebm. <\/p>\n

N\u00ebse TS(T)<\/b> < R-TS(Q)<\/b>, pra q\u00eb t\u00eb dh\u00ebnat tashm\u00eb jan\u00eb lexuar nga nj\u00eb transaksion m\u00eb i ri dhe n\u00ebse b\u00ebhet nj\u00eb ndryshim, do t\u00eb ndodh\u00eb nj\u00eb konflikt. Transaksioni T<\/b> rikthehet. <\/u><\/p>\n

N\u00ebse TS(T)<\/b> < W-TS(Q)<\/b>, pra transaksioni p\u00ebrpiqet t\u00eb shkruaj\u00eb nj\u00eb vler\u00eb m\u00eb t\u00eb re, transaksioni T rikthehet. N\u00eb raste t\u00eb tjera, ndryshimi kryhet dhe W-TS(Q)<\/b> b\u00ebhet i barabart\u00eb me TS(T)<\/b>.<\/u><\/p>\n

Nuk k\u00ebrkohet nd\u00ebrtimi i shtrenjt\u00eb i nj\u00eb grafiku pritjeje. Transaksionet m\u00eb t\u00eb vjetra varen nga ato m\u00eb t\u00eb reja, k\u00ebshtu q\u00eb n\u00eb grafikun e pritjes nuk ka cikle. Nuk ka bllokime reciproke, pasi transaksionet nuk presin, por menj\u00ebher\u00eb rikthehen. Rikthime kaskad\u00eb jan\u00eb t\u00eb mundshme. N\u00ebse Ti<\/b> u rikthye, dhe Tj<\/b> lexoi t\u00eb dh\u00ebna q\u00eb ndryshoi Ti<\/b>, at\u00ebher\u00eb Tj<\/b> duhet t\u00eb rikthehet gjithashtu. N\u00ebse gjat\u00eb k\u00ebsaj Tj<\/b> tashm\u00eb ishte angazhuar, at\u00ebher\u00eb do t\u00eb ndodhte nj\u00eb shkelje e parimit t\u00eb q\u00ebndrueshm\u00ebris\u00eb.<\/p>\n

Nj\u00eb nga zgjidhjet p\u00ebr rikthime kaskad\u00eb. Transaksioni kryen t\u00eb gjitha operacionet sh\u00ebnimi n\u00eb fund, ku transaksionet e tjera jan\u00eb t\u00eb detyruara t\u00eb presin p\u00ebr p\u00ebrfundimin e k\u00ebsaj operacioni. Transaksionet presin angazhimin p\u00ebrpara leximit.<\/p>\n

Rregulli i shkrimit t\u00eb Thomas \u2014 nj\u00eb variacion i metod\u00ebs s\u00eb timestamps ku t\u00eb dh\u00ebnat e p\u00ebrdit\u00ebsuara nga nj\u00eb transaksion m\u00eb i ri nuk lejohet t\u00eb shkruhen nga nj\u00eb m\u00eb t\u00eb vjet\u00ebr.<\/h4>\n

\u0422\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u0438 \u0422\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u0435\u0439 \u043d\u0430\u0437\u044b\u0432\u0430\u0435\u0442\u0441\u044f \u043f\u043e\u0441\u043b\u0435\u0434\u043e\u0432\u0430\u0442\u0435\u043b\u044c\u043d\u043e\u0441\u0442\u044c \u043e\u043f\u0435\u0440\u0430\u0446\u0438\u0439 \u043d\u0430\u0434 \u0434\u0430\u043d\u043d\u044b\u043c\u0438 \u0438\u043c\u0435\u044e\u0449\u0430\u044f \u043d\u0430\u0447\u0430\u043b\u043e \u0438 \u043a\u043e\u043d\u0435\u0446 \u0422\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u044f \u044d\u0442\u043e \u043f\u043e\u0441\u043b\u0435\u0434\u043e\u0432\u0430\u0442\u0435\u043b\u044c\u043d\u043e\u0435 \u0432\u044b\u043f\u043e\u043b\u043d\u0435\u043d\u0438\u0435 \u043e\u043f\u0435\u0440\u0430\u0446\u0438\u0439 \u0447\u0442\u0435\u043d\u0438\u044f \u0438 \u0437\u0430\u043f\u0438\u0441\u0438. \u041e\u043a\u043e\u043d\u0447\u0430\u043d\u0438\u0435\u043c \u0442\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u0438 \u043c\u043e\u0436\u0435\u0442 \u0431\u044b\u0442\u044c \u043b\u0438\u0431\u043e \u0441\u043e\u0445\u0440\u0430\u043d\u0435\u043d\u0438\u0435 \u0438\u0437\u043c\u0435\u043d\u0435\u043d\u0438\u0439 (\u0444\u0438\u043a\u0441\u0430\u0446\u0438\u044f, commit) \u043b\u0438\u0431\u043e \u043e\u0442\u043c\u0435\u043d\u0430 \u0438\u0437\u043c\u0435\u043d\u0435\u043d\u0438\u0439 (\u043e\u0442\u043a\u0430\u0442, rollback). \u041f\u0440\u0438\u043c\u0435\u043d\u0438\u0442\u0435\u043b\u044c\u043d\u043e \u043a \u0411\u0414 \u0442\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u044f \u044d\u0442\u043e \u043d\u0435\u0441\u043a\u043e\u043b\u044c\u043a\u0438\u0445 \u0437\u0430\u043f\u0440\u043e\u0441\u043e\u0432, \u043a\u043e\u0442\u043e\u0440\u044b\u0435 \u0442\u0440\u0430\u043a\u0442\u0443\u044e\u0442\u0441\u044f \u043a\u0430\u043a \u0435\u0434\u0438\u043d\u044b\u0439 \u0437\u0430\u043f\u0440\u043e\u0441. \u0422\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u0438 \u0434\u043e\u043b\u0436\u043d\u044b \u0443\u0434\u043e\u0432\u043b\u0435\u0442\u0432\u043e\u0440\u044f\u0442\u044c \u0441\u0432\u043e\u0439\u0441\u0442\u0432\u0430\u043c ACID \u0410\u0442\u043e\u043c\u0430\u0440\u043d\u043e\u0441\u0442\u044c. \u0422\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u044f \u043b\u0438\u0431\u043e \u0432\u044b\u043f\u043e\u043b\u043d\u044f\u0435\u0442\u0441\u044f \u043f\u043e\u043b\u043d\u043e\u0441\u0442\u044c\u044e […]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[688],"tags":[],"class_list":["post-30878","post","type-post","status-publish","format-standard","hentry","category-administrirovanie"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\n","aioseo_head_json":{"title":"\ud83e\udd47Transaksionet dhe mekanizmat e kontrollit t\u00eb tyre | ProHoster","description":"Transaksionet Nj\u00eb transaksion \u00ebsht\u00eb nj\u00eb sekuenc\u00eb e operacioneve mbi t\u00eb dh\u00ebna q\u00eb ka nj\u00eb fillim dhe nj\u00eb fund. Transaksioni \u00ebsht\u00eb ekzekutimi i radh\u00ebs s\u00eb operacioneve t\u00eb leximit dhe shkruarit. P\u00ebrfundimi i transaksionit mund t\u00eb jet\u00eb ose ruajtja e ndryshimeve (komitimi, commit) ose anulimi i ndryshimeve (rrokja, rollback). N\u00eb lidhje me bazat e t\u00eb dh\u00ebnave, nj\u00eb transaksion \u00ebsht\u00eb disa k\u00ebrkesa q\u00eb interpretohen si nj\u00eb k\u00ebrkes\u00eb e vetme. Transaksionet duhet t\u00eb p\u00ebrmbushin pronat ACID: Atom\u00ebsia. Nj\u00eb transaksion ose realizohet plot\u00ebsisht,","canonical_url":"https:\/\/prohoster.info\/sq\/blog\/administrirovanie\/tranzaktsii-i-mehanizmy-ih-kontrolya","robots":"max-image-preview:large","keywords":"","webmasterTools":{"miscellaneous":""},"schema":null,"og:locale":"sq_AL","og:site_name":"ProHoster | \u041a\u0443\u043f\u0438\u0442\u044c \u043d\u0430\u0434\u0435\u0436\u043d\u044b\u0439 \u0445\u043e\u0441\u0442\u0438\u043d\u0433 \u0434\u043b\u044f \u0441\u0430\u0439\u0442\u043e\u0432 \u0441 \u0437\u0430\u0449\u0438\u0442\u043e\u0439 \u043e\u0442 DDoS, VPS VDS \u0441\u0435\u0440\u0432\u0435\u0440\u044b","og:type":"article","og:title":"\ud83e\udd47\u0422\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u0438 \u0438 \u043c\u0435\u0445\u0430\u043d\u0438\u0437\u043c\u044b \u0438\u0445 \u043a\u043e\u043d\u0442\u0440\u043e\u043b\u044f | ProHoster","og:description":"\u0422\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u0438 \u0422\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u0435\u0439 \u043d\u0430\u0437\u044b\u0432\u0430\u0435\u0442\u0441\u044f \u043f\u043e\u0441\u043b\u0435\u0434\u043e\u0432\u0430\u0442\u0435\u043b\u044c\u043d\u043e\u0441\u0442\u044c \u043e\u043f\u0435\u0440\u0430\u0446\u0438\u0439 \u043d\u0430\u0434 \u0434\u0430\u043d\u043d\u044b\u043c\u0438 \u0438\u043c\u0435\u044e\u0449\u0430\u044f \u043d\u0430\u0447\u0430\u043b\u043e \u0438 \u043a\u043e\u043d\u0435\u0446 \u0422\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u044f \u044d\u0442\u043e \u043f\u043e\u0441\u043b\u0435\u0434\u043e\u0432\u0430\u0442\u0435\u043b\u044c\u043d\u043e\u0435 \u0432\u044b\u043f\u043e\u043b\u043d\u0435\u043d\u0438\u0435 \u043e\u043f\u0435\u0440\u0430\u0446\u0438\u0439 \u0447\u0442\u0435\u043d\u0438\u044f \u0438 \u0437\u0430\u043f\u0438\u0441\u0438. \u041e\u043a\u043e\u043d\u0447\u0430\u043d\u0438\u0435\u043c \u0442\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u0438 \u043c\u043e\u0436\u0435\u0442 \u0431\u044b\u0442\u044c \u043b\u0438\u0431\u043e \u0441\u043e\u0445\u0440\u0430\u043d\u0435\u043d\u0438\u0435 \u0438\u0437\u043c\u0435\u043d\u0435\u043d\u0438\u0439 (\u0444\u0438\u043a\u0441\u0430\u0446\u0438\u044f, commit) \u043b\u0438\u0431\u043e \u043e\u0442\u043c\u0435\u043d\u0430 \u0438\u0437\u043c\u0435\u043d\u0435\u043d\u0438\u0439 (\u043e\u0442\u043a\u0430\u0442, rollback). \u041f\u0440\u0438\u043c\u0435\u043d\u0438\u0442\u0435\u043b\u044c\u043d\u043e \u043a \u0411\u0414 \u0442\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u044f \u044d\u0442\u043e \u043d\u0435\u0441\u043a\u043e\u043b\u044c\u043a\u0438\u0445 \u0437\u0430\u043f\u0440\u043e\u0441\u043e\u0432, \u043a\u043e\u0442\u043e\u0440\u044b\u0435 \u0442\u0440\u0430\u043a\u0442\u0443\u044e\u0442\u0441\u044f \u043a\u0430\u043a \u0435\u0434\u0438\u043d\u044b\u0439 \u0437\u0430\u043f\u0440\u043e\u0441. \u0422\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u0438 \u0434\u043e\u043b\u0436\u043d\u044b \u0443\u0434\u043e\u0432\u043b\u0435\u0442\u0432\u043e\u0440\u044f\u0442\u044c \u0441\u0432\u043e\u0439\u0441\u0442\u0432\u0430\u043c ACID \u0410\u0442\u043e\u043c\u0430\u0440\u043d\u043e\u0441\u0442\u044c. \u0422\u0440\u0430\u043d\u0437\u0430\u043a\u0446\u0438\u044f \u043b\u0438\u0431\u043e \u0432\u044b\u043f\u043e\u043b\u043d\u044f\u0435\u0442\u0441\u044f \u043f\u043e\u043b\u043d\u043e\u0441\u0442\u044c\u044e","og:url":"https:\/\/prohoster.info\/sq\/blog\/administrirovanie\/tranzaktsii-i-mehanizmy-ih-kontrolya","og:image":"https:\/\/prohoster.info\/wp-content\/uploads\/2021\/11\/logo-350.jpg","og:image:secure_url":"https:\/\/prohoster.info\/wp-content\/uploads\/2021\/11\/logo-350.jpg","og:image:width":350,"og:image:height":350,"article:published_time":"2019-10-31T18:37:56+00:00","article:modified_time":"2019-10-31T18:37:56+00:00","article:publisher":"https:\/\/www.facebook.com\/prohoster","article:author":"https:\/\/www.facebook.com\/prohoster"},"aioseo_meta_data":{"post_id":"30878","title":null,"description":null,"keywords":null,"keyphrases":null,"primary_term":null,"canonical_url":null,"og_title":null,"og_description":null,"og_object_type":"default","og_image_type":"default","og_image_url":null,"og_image_width":null,"og_image_height":null,"og_image_custom_url":null,"og_image_custom_fields":null,"og_video":null,"og_custom_url":null,"og_article_section":null,"og_article_tags":null,"twitter_use_og":false,"twitter_card":"default","twitter_image_type":"default","twitter_image_url":null,"twitter_image_custom_url":null,"twitter_image_custom_fields":null,"twitter_title":null,"twitter_description":null,"schema":{"blockGraphs":[],"customGraphs":[],"default":{"data":{"Article":[],"Course":[],"Dataset":[],"FAQPage":[],"Movie":[],"Person":[],"Product":[],"ProductReview":[],"Car":[],"Recipe":[],"Service":[],"SoftwareApplication":[],"WebPage":[]},"graphName":"","isEnabled":true},"graphs":[]},"schema_type":null,"schema_type_options":null,"pillar_content":false,"robots_default":true,"robots_noindex":false,"robots_noarchive":false,"robots_nosnippet":false,"robots_nofollow":false,"robots_noimageindex":false,"robots_noodp":false,"robots_notranslate":false,"robots_max_snippet":null,"robots_max_videopreview":null,"robots_max_imagepreview":"large","priority":null,"frequency":null,"local_seo":null,"seo_analyzer_scan_date":"2026-02-22 15:31:13","breadcrumb_settings":null,"limit_modified_date":false,"reviewed_by":null,"ai":null,"created":"2021-03-01 03:27:38","updated":"2026-02-22 15:31:13","focus_keyword":null,"additional_keywords":null,"truseo_locale":null},"gt_translate_keys":[{"key":"link","format":"url"}],"_links":{"self":[{"href":"https:\/\/prohoster.info\/sq\/wp-json\/wp\/v2\/posts\/30878","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/prohoster.info\/sq\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/prohoster.info\/sq\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/prohoster.info\/sq\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/prohoster.info\/sq\/wp-json\/wp\/v2\/comments?post=30878"}],"version-history":[{"count":1,"href":"https:\/\/prohoster.info\/sq\/wp-json\/wp\/v2\/posts\/30878\/revisions"}],"predecessor-version":[{"id":162008,"href":"https:\/\/prohoster.info\/sq\/wp-json\/wp\/v2\/posts\/30878\/revisions\/162008"}],"wp:attachment":[{"href":"https:\/\/prohoster.info\/sq\/wp-json\/wp\/v2\/media?parent=30878"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/prohoster.info\/sq\/wp-json\/wp\/v2\/categories?post=30878"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/prohoster.info\/sq\/wp-json\/wp\/v2\/tags?post=30878"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}

\nTransaksioni T<\/b> k\u00ebrkon t\u00eb ndryshoj\u00eb t\u00eb dh\u00ebnat Q<\/b>. N\u00ebse TS(T)<\/b> < W-TS(Q)<\/b>, pra transaksioni p\u00ebrpiqet t\u00eb shkruaj\u00eb nj\u00eb vler\u00eb m\u00eb t\u00eb re, transaksioni T nuk rikthehet si n\u00eb metod\u00ebn e timestamps.
\n
Burimi: habr.com<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"