Modifikimet, t\u00eb nevojshme n\u00eb API-n\u00eb Table\/Index AM p\u00ebr t\u00eb mb\u00ebshtetur implementimet alternative t\u00eb MVCC, shqyrtohen me referenc\u00eb n\u00eb zgjerimin OrioleDB, q\u00eb \u00ebsht\u00eb zhvilluar p\u00ebr t\u00eb eliminuar t\u00eb metat e njohura t\u00eb mekanizmit t\u00eb ruajtjes t\u00eb integruar t\u00eb PostgreSQL. Problemi \u00ebsht\u00eb se p\u00ebr integrimin e plot\u00eb t\u00eb OrioleDB me PostgreSQL k\u00ebrkohen ndryshime n\u00eb kodin e PostgreSQL, \u00e7ka e komplikon zbatimin e projektit dhe thekson nevoj\u00ebn p\u00ebr modernizimin e aktualit API Table AM. <\/p>\n
API Table AM nuk imponon drejtp\u00ebrdrejt m\u00ebnyr\u00ebn e implementimit t\u00eb MVCC. Megjithat\u00eb, API Table AM dhe API Index AM b\u00ebjn\u00eb k\u00ebt\u00eb supozim: \u00e7do TID (Tuple\/row Identifier) \u00ebsht\u00eb ose indeksohet nga t\u00eb gjitha indekset, ose nuk indeksohet fare. Madje edhe n\u00ebse Index AM ka disa referenca p\u00ebr nj\u00eb TID (p.sh., GIN), t\u00eb gjitha k\u00ebto referenca duhet t\u00eb korrespondohen me nj\u00eb vler\u00eb t\u00eb indeksuar t\u00eb nj\u00ebjt\u00eb.
![\"Zhvilluesit](\"\/wp-content\/uploads\/2025\/04\/a2082618f49d887e6987a73c65091c59.png\")
<\/center> <\/p>\nKy ky\u00e7 p\u00ebsoj kritik\u00eb p\u00ebr rritjen e numrit t\u00eb operacioneve t\u00eb shkruar (\"shkruaj amplifikim\") \u2014 n\u00ebse p\u00ebrdit\u00ebsohet nj\u00eb atribut i indeksuar, \u00ebsht\u00eb e nevojshme t\u00eb p\u00ebrdit\u00ebsohen t\u00eb gjith\u00eb indeks\u00ebt n\u00eb tabel\u00eb. P\u00ebr t\u00eb shfryt\u00ebzuar plot\u00ebsisht p\u00ebrfitimet e regjistrit UNDO ose p\u00ebr t\u00eb nd\u00ebrtuar nj\u00eb metod\u00eb tjet\u00ebr ruajtje pa \"amplifikimin e shkruar\" (p.sh., metoda WARM), \u00ebsht\u00eb e nevojshme t\u00eb prishim k\u00ebt\u00eb supozim.
![\"Zhvilluesit](\"\/wp-content\/uploads\/2025\/04\/da5adbec63e0b4c139733c5775b317b9.png\")
<\/center> <\/p>\nTable AM i bazuar n\u00eb UNDO, q\u00eb nuk do t\u00eb shkel\u00eb k\u00ebt\u00eb supozim, i ngjan metod\u00ebs ekzistuese HOT (Heap-Only Tuples), p\u00ebrve\u00e7 q\u00eb versionet e vjetra t\u00eb rreshtave ruhen n\u00eb ditarin UNDO dhe nuk duhet t\u00eb ngjiten n\u00eb t\u00eb nj\u00ebjt\u00ebn faqe. Por, sipas autor\u00ebve, k\u00ebtij avantazhi i mungon e drejta p\u00ebr t\u00eb justifikuar ekzistenc\u00ebn e nj\u00eb Table AM t\u00eb ve\u00e7ant\u00eb. <\/p>\n
Kufizimet praktike t\u00eb API-t aktual: <\/p>\n
- \n
- Gjat\u00eb p\u00ebrdit\u00ebsimit t\u00eb nj\u00eb rreshti t\u00eb tabel\u00ebs, indeks\u00ebt p\u00ebrdit\u00ebsohen sipas parimit \"t\u00eb gjith\u00eb ose asgj\u00eb\".\n
- Mungesa n\u00eb API-n\u00eb Index AM t\u00eb mund\u00ebsis\u00eb p\u00ebr fshirjen e pikave t\u00eb caktuara t\u00eb caktueseve. Tani \u00ebsht\u00eb e mundur t\u00eb fshihen rreshtat nga indekset n\u00eb m\u00ebnyr\u00eb masive p\u00ebrmes metodave ambulkdelete dhe amvacuumcleanup. P\u00ebrpjekja p\u00ebr t\u00eb realizuar fshirjen e pikave t\u00eb caktuara p\u00ebrmes k\u00ebtij API do t\u00eb sillte efikasitet t\u00eb ul\u00ebt, pasi shumica e implementimeve aktuale duhet t\u00eb skanojn\u00eb t\u00eb gjith\u00eb indeksin. P\u00ebrve\u00e7 k\u00ebsaj, API nuk lejon t\u00eb specifikohet se cilat nga caktuese t\u00eb lidhur me t\u00eb nj\u00ebjtin TID duhet t\u00eb fshihen. Ai mund t\u00eb fshij\u00eb vet\u00ebm t\u00eb gjith\u00eb.\n
- Indeks\u00ebt aktualisht referohen n\u00eb rreshtat e tabel\u00ebs n\u00ebp\u00ebrmjet numrit t\u00eb bllokut (32 bit) dhe numrit t\u00eb zhvendosjes (16 bit). Dhe vet\u00ebm 11 bit t\u00eb numrit t\u00eb zhvendosjes mund t\u00eb transmetohen n\u00eb m\u00ebnyr\u00eb t\u00eb sigurt nga TID i tabel\u00ebs n\u00eb t\u00eb gjitha metodat e qasjes s\u00eb indeksit. N\u00eb k\u00ebt\u00eb rast, realizimet alternative t\u00eb MVCC mund t\u00eb ken\u00eb nevoj\u00eb t\u00eb ruajn\u00eb nj\u00eb ngarkes\u00eb shtes\u00eb (payload) s\u00eb bashku me TID. P\u00ebr shembull, n\u00eb OrioleDB k\u00ebrkohet nj\u00eb ose disa bit p\u00ebr t\u00eb realizuar indeks\u00ebt \"delete-marking\" ose informacionin e plot\u00eb t\u00eb dukshm\u00ebris\u00eb. <\/ul>\n
Jan\u00eb propozuar dy m\u00ebnyra p\u00ebr t\u00eb kap\u00ebrcyer kufizimet n\u00eb praktik\u00eb: <\/p>\n
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Qasja 1: API Index AM ofron mund\u00ebsi p\u00ebr implementimin alternativ t\u00eb MVCC. <\/p>\n
Nd\u00ebrsa Table AM vazhdon t\u00eb jet\u00eb p\u00ebrgjegj\u00ebs p\u00ebr t\u00eb gjitha komponent\u00ebt e MVCC, Index AM ofron mund\u00ebsit\u00eb e nevojshme p\u00ebr realizimin alternativ t\u00eb MVCC, konkretisht: ruajtjen e ngarkes\u00ebs p\u00ebrdoruese (payload) s\u00eb bashku me TID, metod\u00ebn e fshirjes pik\u00eb-pik\u00eb dhe madje metod\u00ebn e p\u00ebrdit\u00ebsimit pik\u00eb-pik\u00eb (n\u00ebse TID n\u00eb indeks nuk mund t\u00eb ndryshohet, ngarkesa p\u00ebrdoruese \u2013 mundet). P\u00ebrve\u00e7 k\u00ebsaj, pasi \u00ebsht\u00eb e nevojshme q\u00eb disa tuple t\u00eb indeksit t\u00eb referohen n\u00eb t\u00eb nj\u00ebjtin TID, metodat API t\u00eb aplikuara gjat\u00eb skanimit t\u00eb indeksit gjithashtu k\u00ebrkojn\u00eb p\u00ebrdit\u00ebsim. <\/p>\n
Qasja 2: Indekset q\u00eb mb\u00ebshtesin MVCC. <\/p>\n
Nj\u00eb alternativ\u00eb do t\u00eb ishte t\u00eb lejohej indeks\u00ebt q\u00eb mb\u00ebshtesin MVCC. K\u00ebshtu, \"executor\" (ose ndoshta Table AM) thjesht th\u00ebrret metodat insert() dhe delete() n\u00eb Index AM, nd\u00ebrsa Index AM ofron mund\u00ebsin\u00eb e skanimit duke marr\u00eb n\u00eb konsiderat\u00eb MVCC. Kjo do ta thjeshtonte ndjesh\u00ebm skanimin duke p\u00ebrdorur vet\u00ebm indeks\u00ebt (index-only). Edhe i gjith\u00eb Table AM n\u00eb k\u00ebt\u00eb rast mund t\u00eb b\u00ebhet nj\u00eb shkall\u00eb nd\u00ebrmjet\u00ebse q\u00eb ruan t\u00eb dh\u00ebnat n\u00eb indeks. <\/p>\n
N\u00eb diagramin m\u00eb posht\u00eb tregohet nj\u00eb shembull. Vlera e indeksit 2 p\u00ebrdit\u00ebsohet nga transaksioni 11 nga vlera \"A\" n\u00eb vler\u00ebn \"B\". Prandaj, vlera \"A\" \u00ebsht\u00eb sh\u00ebnuar si xmax == 11, nd\u00ebrsa vlera \"B\" \u00ebsht\u00eb sh\u00ebnuar si xmin == 11. K\u00ebshtu, mund t\u00eb skanohet indeksi 2 dhe t\u00eb merren vet\u00ebm tuple t\u00eb dukshme sipas MVCC pa kontrollet e grumbullit (heap). Mir\u00ebmbajtja e indekseve 2 gjithashtu mund t\u00eb realizohet pa p\u00ebrdorur grumbullin.
![\"Zhvilluesit](\"\/wp-content\/uploads\/2025\/04\/9103127cc51f83c824c6cdc22135b470.png\")
<\/center> <\/p>\nMe implementimin e t\u00eb gjitha risive t\u00eb p\u00ebrmendura n\u00eb API-n\u00eb e metodave t\u00eb indeksit p\u00ebr qasje, \u00ebsht\u00eb shum\u00eb e pamundur q\u00eb t\u00eb p\u00ebrfundojn\u00eb t\u00eb gjitha indiket p\u00ebr mb\u00ebshtetje t\u00eb gjitha mund\u00ebsive t\u00eb reja nj\u00ebher\u00ebsh. M\u00eb realiste \u00ebsht\u00eb t\u00eb lejohet disa realizime p\u00ebr nj\u00eb metod\u00eb t\u00eb vetme qasjeje n\u00eb indeks. P\u00ebr shembull, n\u00eb p\u00ebrve\u00e7 t\u00eb B-tree standarde, zgjerimi do t\u00eb ishte n\u00eb gjendje t\u00eb implementonte nj\u00eb B-tree alternativ me mb\u00ebshtetje p\u00ebr MVCC brenda indeksit dhe mb\u00ebshtetje p\u00ebr identifikator\u00eb regjistrimesh n\u00eb gjat\u00ebsi t\u00eb rast\u00ebsishme.
![\"Zhvilluesit](\"\/wp-content\/uploads\/2025\/04\/57e1c15ecdd08f7b8095f464b59523b9.png\")
<\/center> <\/p>\n