V\u00fdvoj\u00e1\u0159i projektu SQLite zah\u00e1jili testov\u00e1n\u00ed experiment\u00e1ln\u00edho backendu HCtree, kter\u00fd podporuje z\u00e1mky na \u00farovni \u0159\u00e1dk\u016f a zaji\u0161\u0165uje vysokou \u00farove\u0148 paralelizace p\u0159i zpracov\u00e1n\u00ed dotaz\u016f. Nov\u00fd backend je zam\u011b\u0159en na zv\u00fd\u0161en\u00ed efektivity vyu\u017eit\u00ed SQLite v klient-server syst\u00e9mech, kde je t\u0159eba zpracov\u00e1vat velk\u00e9 mno\u017estv\u00ed simult\u00e1nn\u00edch z\u00e1pisov\u00fdch dotaz\u016f do datab\u00e1ze. <\/p>\n
Struktury b-tree, p\u016fvodn\u011b pou\u017e\u00edvan\u00e9 v SQLite pro ukl\u00e1d\u00e1n\u00ed dat, nejsou p\u0159izp\u016fsobeny takov\u00e9mu zat\u00ed\u017een\u00ed, co\u017e omezuje SQLite na mo\u017enost z\u00e1pisu pouze v jednom vl\u00e1kn\u011b. Jako experiment za\u010dali v\u00fdvoj\u00e1\u0159i rozv\u00edjet alternativn\u00ed \u0159e\u0161en\u00ed, kter\u00e9 pou\u017e\u00edv\u00e1 pro skladov\u00e1n\u00ed strukturu HC-tree, vhodn\u011bj\u0161\u00ed pro paralelizaci z\u00e1pisov\u00fdch operac\u00ed. <\/p>\n
Pro organizaci paraleln\u00edho prov\u00e1d\u011bn\u00ed v\u00edce z\u00e1pisov\u00fdch operac\u00ed v HCtree se pou\u017e\u00edv\u00e1 mechanismus d\u011blen\u00ed transakc\u00ed, kter\u00fd vyu\u017e\u00edv\u00e1 z\u00e1mky na \u00farovni str\u00e1nek a je podobn\u00fd MVCC (v\u00edceverzn\u00ed \u0159\u00edzen\u00ed sou\u010dasn\u00e9ho p\u0159\u00edstupu), ale pou\u017e\u00edv\u00e1 kontroly transakc\u00ed na z\u00e1klad\u011b kl\u00ed\u010d\u016f a rozsah\u016f kl\u00ed\u010d\u016f nam\u00edsto sad str\u00e1nek. Operace \u010dten\u00ed a z\u00e1pisu se prov\u00e1d\u011bj\u00ed v\u00e1z\u00e1ny na snapshot datab\u00e1ze, jeho\u017e zm\u011bny se stanou viditeln\u00fdmi v hlavn\u00ed datab\u00e1zi a\u017e po dokon\u010den\u00ed transakce. <\/p>\n
Klienti mohou pou\u017e\u00edt t\u0159i operace pro zah\u00e1jen\u00ed transakc\u00ed: <\/p>\n
HCtree podporuje replikaci ve stylu \u201emaster-slave\u201c, co\u017e umo\u017e\u0148uje p\u0159en\u00e1\u0161et transakce do jin\u00e9 DB a udr\u017eovat sekund\u00e1rn\u00ed DB v synchronizovan\u00e9m stavu s hlavn\u00ed DB. HCtree tak\u00e9 odstra\u0148uje omezen\u00ed velikosti DB \u2014 m\u00edsto 32bitov\u00fdch identifik\u00e1tor\u016f str\u00e1nek dat se v HCtree pou\u017e\u00edvaj\u00ed 48bitov\u00e9, co\u017e zvy\u0161uje maxim\u00e1ln\u00ed velikost DB z 16 tebibyte na 1 exbibyte (milion tebibyte). O\u010dek\u00e1v\u00e1 se, \u017ee v\u00fdkonnost SQLite s backendem HCtree nebude ni\u017e\u0161\u00ed ne\u017e u klasick\u00e9ho jednovl\u00e1knov\u00e9ho backendu. Klienti SQLite s podporou HCtree budou moci p\u0159istupovat jak k DB zalo\u017een\u00e9 na struktu\u0159e HC-tree, tak ke star\u00fdm DB SQLite. \u0420\u0430\u0437\u0440\u0430\u0431\u043e\u0442\u0447\u0438\u043a\u0438 \u043f\u0440\u043e\u0435\u043a\u0442\u0430 SQLite \u043d\u0430\u0447\u0430\u043b\u0438 \u0442\u0435\u0441\u0442\u0438\u0440\u043e\u0432\u0430\u043d\u0438\u0435 \u044d\u043a\u0441\u043f\u0435\u0440\u0438\u043c\u0435\u043d\u0442\u0430\u043b\u044c\u043d\u043e\u0433\u043e \u0431\u044d\u043a\u0435\u043d\u0434\u0430 HCtree, \u043f\u043e\u0434\u0434\u0435\u0440\u0436\u0438\u0432\u0430\u044e\u0449\u0435\u0433\u043e \u0431\u043b\u043e\u043a\u0438\u0440\u043e\u0432\u043a\u0443 \u043d\u0430 \u0443\u0440\u043e\u0432\u043d\u0435 \u0441\u0442\u0440\u043e\u043a (row) \u0438 \u043e\u0431\u0435\u0441\u043f\u0435\u0447\u0438\u0432\u0430\u044e\u0449\u0435\u0433\u043e \u0432\u044b\u0441\u043e\u043a\u0438\u0439 \u0443\u0440\u043e\u0432\u0435\u043d\u044c \u0440\u0430\u0441\u043f\u0430\u0440\u0430\u043b\u043b\u0435\u043b\u0438\u0432\u0430\u043d\u0438\u044f \u043f\u0440\u0438 \u043e\u0431\u0440\u0430\u0431\u043e\u0442\u043a\u0435 \u0437\u0430\u043f\u0440\u043e\u0441\u043e\u0432. \u041d\u043e\u0432\u044b\u0439 \u0431\u044d\u043a\u0435\u043d\u0434 \u043d\u0430\u0446\u0435\u043b\u0435\u043d \u043d\u0430 \u043f\u043e\u0432\u044b\u0448\u0435\u043d\u0438\u0435 \u044d\u0444\u0444\u0435\u043a\u0442\u0438\u0432\u043d\u043e\u0441\u0442\u0438 \u0438\u0441\u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u043d\u0438\u044f SQLite \u0432 \u043a\u043b\u0438\u0435\u043d\u0442-\u0441\u0435\u0440\u0432\u0435\u0440\u043d\u044b\u0445 \u0441\u0438\u0441\u0442\u0435\u043c\u0430\u0445, \u0432 \u043a\u043e\u0442\u043e\u0440\u044b\u0445 \u043f\u0440\u0438\u0445\u043e\u0434\u0438\u0442\u0441\u044f \u043e\u0431\u0440\u0430\u0431\u0430\u0442\u044b\u0432\u0430\u0442\u044c \u0431\u043e\u043b\u044c\u0448\u043e\u0435 \u0447\u0438\u0441\u043b\u043e \u043e\u0434\u043d\u043e\u0432\u0440\u0435\u043c\u0435\u043d\u043d\u044b\u0445 \u0437\u0430\u043f\u0440\u043e\u0441\u043e\u0432 \u043a \u0411\u0414 \u043d\u0430 \u0437\u0430\u043f\u0438\u0441\u044c. \u0421\u0442\u0440\u0443\u043a\u0442\u0443\u0440\u044b b-tree, \u0438\u0437\u043d\u0430\u0447\u0430\u043b\u044c\u043d\u043e \u043f\u0440\u0438\u043c\u0435\u043d\u044f\u0435\u043c\u044b\u0435 \u0432 SQLite \u0434\u043b\u044f \u0445\u0440\u0430\u043d\u0435\u043d\u0438\u044f \u0434\u0430\u043d\u043d\u044b\u0445, \u043d\u0435 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Zdroj: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"