Tw\u00f3rcy projektu SQLite rozpocz\u0119li testowanie eksperymentalnego backendu HCtree, kt\u00f3ry wspiera blokady na poziomie wierszy i zapewnia wysoki poziom r\u00f3wnoleg\u0142ego przetwarzania zapyta\u0144. Nowy backend ma na celu zwi\u0119kszenie efektywno\u015bci wykorzystania SQLite w systemach kliencko-serwerowych, kt\u00f3re musz\u0105 obs\u0142ugiwa\u0107 du\u017c\u0105 liczb\u0119 r\u00f3wnoczesnych zapis\u00f3w do bazy danych. <\/p>\n
Struktury b-drzew, kt\u00f3re pierwotnie by\u0142y wykorzystywane w SQLite do przechowywania danych, nie s\u0105 przystosowane do tego typu obci\u0105\u017cenia, co ogranicza SQLite do zapisu tylko w jednym w\u0105tku. W ramach eksperymentu, tw\u00f3rcy zacz\u0119li rozwija\u0107 alternatywne rozwi\u0105zanie, kt\u00f3re stosuje struktur\u0119 HC-tree, bardziej odpowiedni\u0105 do r\u00f3wnoleg\u0142ego przetwarzania operacji zapisu. <\/p>\n
Aby zorganizowa\u0107 r\u00f3wnoczesne wykonywanie wielu operacji w HCtree, zosta\u0142a zastosowana mechanizm podzia\u0142u transakcji, wykorzystuj\u0105cy blokady na poziomie stron, podobny do MVCC (wielowersyjnego zarz\u0105dzania dost\u0119pem wsp\u00f3\u0142bie\u017cnym), jednak oparty na weryfikacjach transakcji w oparciu o klucze i zakresy kluczy, a nie zestawy stron. Operacje odczytu i zapisu s\u0105 zwi\u0105zane z migawk\u0105 bazy danych, a ich zmiany staj\u0105 si\u0119 widoczne w g\u0142\u00f3wnej bazie danych dopiero po zako\u0144czeniu transakcji. <\/p>\n
Klienci mog\u0105 korzysta\u0107 z trzech operacji otwierania transakcji: <\/p>\n
HCtree wspiera replikacj\u0119 w stylu «master-slave», umo\u017cliwiaj\u0105c przenoszenie transakcji do innej bazy danych i utrzymanie wt\u00f3rnych baz danych w stanie zsynchronizowanym z g\u0142\u00f3wn\u0105 baz\u0105 danych. HCtree r\u00f3wnie\u017c znosi ograniczenie na rozmiar bazy danych — zamiast 32-bitowych identyfikator\u00f3w stron danych w HCtree stosowane s\u0105 48-bitowe, co zwi\u0119ksza maksymalny rozmiar bazy danych z 16 tebibajt\u00f3w do 1 eksbibajta (milion tebibajt\u00f3w). Oczekuje si\u0119, \u017ce wydajno\u015b\u0107 SQLite z backendem HCtree b\u0119dzie nie ni\u017csza ni\u017c klasycznego jednopoziomowego backendu. Klienci SQLite z obs\u0142ug\u0105 HCtree b\u0119d\u0105 mogli uzyskiwa\u0107 dost\u0119p zar\u00f3wno do baz danych opartych na strukturze HC-tree, jak i do starych baz danych 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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\u0179r\u00f3d\u0142o: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"