{"id":36650,"date":"2019-10-31T22:12:54","date_gmt":"2019-10-31T19:12:54","guid":{"rendered":"https:\/\/prohoster.info\/blog\/tranzaktsii-v-globalah-intersystems-iris\/"},"modified":"2019-10-31T22:12:54","modified_gmt":"2019-10-31T19:12:54","slug":"tranzaktsii-v-globalah-intersystems-iris","status":"publish","type":"post","link":"https:\/\/prohoster.info\/cs\/blog\/administrirovanie\/tranzaktsii-v-globalah-intersystems-iris","title":{"rendered":"Transakce v glob\u00e1lech InterSystems IRIS","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

\"TransakceDatab\u00e1zov\u00fd syst\u00e9m InterSystems IRIS podporuje zaj\u00edmav\u00e9 struktury pro ukl\u00e1d\u00e1n\u00ed dat \u2014 glob\u00e1ly. V podstat\u011b se jedn\u00e1 o v\u00edcerozm\u011brn\u00e9 kl\u00ed\u010de s r\u016fzn\u00fdmi dodate\u010dn\u00fdmi funkcemi, jako jsou transakce, rychl\u00e9 funkce pro proch\u00e1zen\u00ed datov\u00fdch strom\u016f, z\u00e1mky a vlastn\u00ed jazyk ObjectScript.<\/p>\n

V\u00edce o glob\u00e1lech v s\u00e9rii \u010dl\u00e1nk\u016f \u201eGlob\u00e1ly \u2014 \u010darod\u011bjnick\u00e9 me\u010de pro ukl\u00e1d\u00e1n\u00ed dat\u201c:<\/p>\n

Stromy. \u010c\u00e1st 1<\/a><\/noindex>
\nStromy. \u010c\u00e1st 2<\/a><\/noindex>
\n\u0158\u00eddk\u00e9 pole. \u010c\u00e1st 3<\/a><\/noindex><\/p>\n

Za\u010dalo m\u011b zaj\u00edmat, jak jsou realizov\u00e1ny transakce v glob\u00e1lech, jak\u00e9 maj\u00ed specifika. V\u017edy\u0165 se jedn\u00e1 o zcela jinou strukturu pro ukl\u00e1d\u00e1n\u00ed dat ne\u017e n\u00e1m obecn\u011b zn\u00e1m\u00e9 tabulky. Mnohem n\u00edzko\u00farov\u0148ov\u011bj\u0161\u00ed.
\n<\/a><\/noindex>
\nJak je zn\u00e1mo z teorie rela\u010dn\u00edch datab\u00e1z\u00ed, dobr\u00e1 realizace transakc\u00ed by m\u011bla spl\u0148ovat po\u017eadavky ACID<\/a><\/noindex>:<\/p>\n

A \u2014 Atomicita.<\/b> Zaznamen\u00e1vaj\u00ed se v\u0161echny zm\u011bny proveden\u00e9 v transakci nebo \u017e\u00e1dn\u00e9.<\/p>\n

C \u2014 Konzistence.<\/b> Po dokon\u010den\u00ed transakce mus\u00ed b\u00fdt logick\u00fd stav datab\u00e1ze intern\u011b nekontradiktorn\u00ed. Velmi \u010dasto se tento po\u017eadavek t\u00fdk\u00e1 program\u00e1tor\u016f, ale v p\u0159\u00edpad\u011b SQL datab\u00e1z\u00ed se to t\u00fdk\u00e1 tak\u00e9 ciz\u00edch kl\u00ed\u010d\u016f.<\/p>\n

I \u2014 Izolace.<\/b> Soub\u011b\u017en\u011b prov\u00e1d\u011bn\u00e9 transakce by na sebe nem\u011bly m\u00edt vliv.<\/p>\n

D \u2014 Trvanlivost.<\/b> Po \u00fasp\u011b\u0161n\u00e9m dokon\u010den\u00ed transakce by probl\u00e9my na ni\u017e\u0161\u00edch \u00farovn\u00edch (nap\u0159\u00edklad v\u00fdpadek nap\u00e1jen\u00ed) nem\u011bly ovlivnit data zm\u011bn\u011bn\u00e1 transakc\u00ed.<\/p>\n

Glob\u00e1ly jsou nerela\u010dn\u00ed datov\u00e9 struktury. Byly navr\u017eeny pro extr\u00e9mn\u011b rychlou pr\u00e1ci na velmi omezen\u00e9m hardwaru. Poj\u010fme se pod\u00edvat na realizaci transakc\u00ed v glob\u00e1lech pomoc\u00ed ofici\u00e1ln\u00edho docker obrazu IRIS<\/a><\/noindex>.<\/p>\n

Pro podporu transakc\u00ed v IRIS se pou\u017e\u00edvaj\u00ed p\u0159\u00edkazy: TSTART<\/a><\/noindex>, TCOMMIT<\/a><\/noindex>, TROLLBACK<\/a><\/noindex>.<\/p>\n

1. Atomicita<\/h2>\n

\nNejjednodu\u0161eji lze ov\u011b\u0159it atomicitu. Ov\u011b\u0159\u00edme z konzole datab\u00e1ze.<\/p>\n

Kill ^a\nTSTART\nSet ^a(1) = 1\nSet ^a(2) = 2\nSet ^a(3) = 3\nTCOMMIT<\/code><\/pre>\n
\nPak provedeme v\u00fdstup:<\/p>\n
Write ^a(1), \u201c \u201d, ^a(2), \u201c \u201d, ^a(3)<\/code><\/pre>\n
\nDostaneme:<\/p>\n
1 2 3<\/code><\/pre>\n
\nV\u0161echno je v po\u0159\u00e1dku. Atomicita byla dodr\u017eena: v\u0161echny zm\u011bny byly zaps\u00e1ny.<\/p>\n
Zt\u00ed\u017e\u00edme \u00fakol, zavedeme chybu a pod\u00edv\u00e1me se, jak se transakce uchov\u00e1, \u010d\u00e1ste\u010dn\u011b nebo v\u016fbec.<\/p>\n
Je\u0161t\u011b jednou ov\u011b\u0159\u00edme atomicitu:<\/p>\n
Kill ^A\nTSTART\nSet ^a(1) = 1\nSet ^a(2) = 2\nSet ^a(3) = 3<\/code><\/pre>\n
\nPot\u00e9 n\u00e1siln\u011b zastav\u00edme kontejner, spust\u00edme ho a pod\u00edv\u00e1me se. <\/p>\n
docker kill my-iris<\/code><\/pre>\n
\nTento p\u0159\u00edkaz je prakticky ekvivalentn\u00ed n\u00e1siln\u00e9mu vypnut\u00ed nap\u00e1jen\u00ed, proto\u017ee pos\u00edl\u00e1 sign\u00e1l okam\u017eit\u00e9ho zastaven\u00ed procesu SIGKILL.<\/p>\n
Mohla \u010d\u00e1ste\u010dn\u011b z\u016fstat transakce?<\/p>\n
WRITE ^a(1), ^a(2), ^a(3)\n^\n ^a(1)<\/code><\/pre>\n
\n \u2014 Ne, nez\u016fstala.<\/p>\n
Vyzkou\u0161\u00edme p\u0159\u00edkaz pro vr\u00e1cen\u00ed:<\/p>\n
Kill ^A\nTSTART\nSet ^a(1) = 1\nSet ^a(2) = 2\nSet ^a(3) = 3\nTROLLBACK\n\nWRITE ^a(1), ^a(2), ^a(3)\n^\n ^a(1)<\/code><\/pre>\n
\nTak\u00e9 se nic nezachovalo.<\/p>\n
2. Konzistence<\/h2>\n
\nProto\u017ee v glob\u00e1ln\u00edch datech jsou kl\u00ed\u010de tak\u00e9 tvo\u0159eny na glob\u00e1lech (p\u0159ipom\u00edn\u00e1m, \u017ee global je struktura ni\u017e\u0161\u00ed \u00farovn\u011b pro ukl\u00e1d\u00e1n\u00ed dat ne\u017e rela\u010dn\u00ed tabulka), pro spln\u011bn\u00ed po\u017eadavku na konzistenci je t\u0159eba zahrnout zm\u011bnu kl\u00ed\u010de do t\u00e9\u017ee transakce, co i zm\u011bnu glob\u00e1lu.<\/p>\n
Nap\u0159\u00edklad m\u00e1me global ^person, v n\u011bm\u017e uchov\u00e1v\u00e1me osoby a jako kl\u00ed\u010d pou\u017e\u00edv\u00e1me I\u010cO.<\/p>\n
^person(1234567, \u2018firstname\u2019) = \u2018Sergey\u2019\n^person(1234567, \u2018lastname\u2019) = \u2018Kamenev\u2019\n^person(1234567, \u2018phone\u2019) = \u2018+74995555555\n...<\/code><\/pre>\n
\nAbychom dos\u00e1hli rychl\u00e9ho hled\u00e1n\u00ed podle p\u0159\u00edjmen\u00ed a jm\u00e9na, vytvo\u0159ili jsme kl\u00ed\u010d ^index.<\/p>\n
^index(\u2018Kamenev\u2019, \u2018Sergey\u2019, 1234567) = 1<\/code><\/pre>\n
\nAby datab\u00e1ze byla konzistentn\u00ed, mus\u00edme p\u0159id\u00e1vat osobu takto:<\/p>\n
TSTART\n^person(1234567, \u2018firstname\u2019) = \u2018Sergey\u2019\n^person(1234567, \u2018lastname\u2019) = \u2018Kamenev\u2019\n^person(1234567, \u2018phone\u2019) = \u2018+74995555555\n^index(\u2018Kamenev\u2019, \u2018Sergey\u2019, 1234567) = 1\nTCOMMIT<\/code><\/pre>\n
\nPokud jde o maz\u00e1n\u00ed, tak\u00e9 mus\u00edme pou\u017e\u00edt transakci:<\/p>\n
TSTART\nKill ^person(1234567)\nZKill ^index(\u2018Kamenev\u2019, \u2018Sergey\u2019, 1234567)\nTCOMMIT<\/code><\/pre>\n
\nJin\u00fdmi slovy, spln\u011bn\u00ed po\u017eadavku na konzistenci le\u017e\u00ed pln\u011b na ramenou program\u00e1tora. Ale kdy\u017e jde o glob\u00e1ly, je to norm\u00e1ln\u00ed vzhledem k jejich n\u00edzk\u00e9 \u00farovni.<\/p>\n
3. Izolace<\/h2>\n
\nTady za\u010d\u00edn\u00e1 chaos. Mnoho u\u017eivatel\u016f sou\u010dasn\u011b pracuje na stejn\u00e9 datab\u00e1zi, m\u011bn\u00ed stejn\u00e9 \u00fadaje.<\/p>\n
Situace se d\u00e1 p\u0159irovnat k tomu, kdy\u017e mnoho u\u017eivatel\u016f sou\u010dasn\u011b pracuje se stejn\u00fdm repozit\u00e1\u0159em k\u00f3du a sna\u017e\u00ed se sou\u010dasn\u011b commitovat zm\u011bny do mnoha soubor\u016f najednou.<\/p>\n
Datab\u00e1ze to mus\u00ed zvl\u00e1dat v re\u00e1ln\u00e9m \u010dase. Vzhledem k tomu, \u017ee ve v\u00e1\u017en\u00fdch firm\u00e1ch existuje i speci\u00e1ln\u00ed osoba, kter\u00e1 se star\u00e1 o kontrolu verz\u00ed (o slou\u010den\u00ed v\u011btv\u00ed, vy\u0159e\u0161en\u00ed konflikt\u016f atd.), a datab\u00e1ze to v\u0161echno mus\u00ed d\u011blat v re\u00e1ln\u00e9m \u010dase, je obt\u00ed\u017enost \u00fakolu a spr\u00e1vnost n\u00e1vrhu datab\u00e1ze a k\u00f3du, kter\u00fd ji spravuje, jasn\u00e1.<\/p>\n
Datab\u00e1ze nem\u016f\u017ee pochopit smysl akc\u00ed prov\u00e1d\u011bn\u00fdch u\u017eivateli, aby zabr\u00e1nila konflikt\u016fm, pokud pracuj\u00ed se stejn\u00fdmi daty. M\u016f\u017ee pouze zru\u0161it jednu transakci, kter\u00e1 je v rozporu s jinou, nebo je prov\u00e9st po sob\u011b.<\/p>\n
Dal\u0161\u00edm probl\u00e9mem je, \u017ee b\u011bhem prov\u00e1d\u011bn\u00ed transakce (p\u0159ed potvrzen\u00edm) m\u016f\u017ee b\u00fdt stav datab\u00e1ze nekonzistentn\u00ed, a proto je \u017e\u00e1douc\u00ed, aby m\u011bli ostatn\u00ed transakce omezen\u00fd p\u0159\u00edstup k nekonzistentn\u00edmu stavu datab\u00e1ze, co\u017e se v rela\u010dn\u00edch DB dosahuje mnoha zp\u016fsoby: vytv\u00e1\u0159en\u00edm sn\u00edmk\u016f, v\u00edce verzemi \u0159\u00e1dk\u016f atd.<\/p>\n
P\u0159i paraleln\u00edm prov\u00e1d\u011bn\u00ed transakc\u00ed je d\u016fle\u017eit\u00e9, aby si navz\u00e1jem nep\u0159ek\u00e1\u017eely. To je vlastnost izolace.<\/p>\n
SQL definuje 4 \u00farovn\u011b izolace:<\/p>\n