{"id":72265,"date":"2020-03-03T08:42:17","date_gmt":"2020-03-03T05:42:17","guid":{"rendered":"https:\/\/prohoster.info\/blog\/postgresql-antipatterns-menyaem-dannye-v-obhod-triggera"},"modified":"2020-03-03T16:13:51","modified_gmt":"2020-03-03T13:13:51","slug":"postgresql-antipatterns-menyaem-dannye-v-obhod-triggera","status":"publish","type":"post","link":"https:\/\/prohoster.info\/no\/blog\/administrirovanie\/postgresql-antipatterns-menyaem-dannye-v-obhod-triggera","title":{"rendered":"PostgreSQL Antipatterns: endre data utenom trigger","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p>Tid eller annet veit mange at dei m\u00e5 gjere ei masseoppdatering i tabellar. Eg har allereie <noindex><a rel=\"nofollow\" href=\"https:\/\/habr.com\/post\/481610\/\">fortalt om korleis dette kan gjerast best<\/a><\/noindex>, og om korleis det er best \u00e5 unng\u00e5 det. I dag vil eg ta for meg den andre aspekten ved masseoppdatering \u2014 <b>utl\u00f8sing av triggarar<\/b>.<\/p>\n<p>For eksempel, i tabellen der du m\u00e5 gjere endringar, heng det ein ondskapsfull trigger <code>ON UPDATE<\/code>, som flyttar alle endringar til nokre aggregat. Og du m\u00e5 oppdatere alt (for eksempel initialisere eit nytt felt) s\u00e5 forsiktig at desse aggregata ikkje blir p\u00e5verka.<\/p>\n<h2>La oss berre sl\u00e5 av triggerane!<\/h2>\n<p><\/p>\n<pre><code class=\"sql\">BEGIN;\n  ALTER TABLE ... DISABLE TRIGGER ...;\n  UPDATE ...; -- her tar det tid\n  ALTER TABLE ... ENABLE TRIGGER ...;\nCOMMIT;<\/code><\/pre>\n<p>\nEigentleg er det alt \u2014 <b>alt heng i<\/b>.<\/p>\n<p>Fordi <code>ALTER TABLE<\/code> det p\u00e5leggjer <b>AccessExclusive<\/b>-l\u00e5sing, som gjer at ingen som st\u00e5r parallel med sp\u00f8rsm\u00e5let, til og med ein enkel <code>SELECT<\/code>, kan lese noko fr\u00e5 tabellen. Dette betyr at s\u00e5 lenge denne transaksjonen ikkje er avslutta, vil dei som vil nysgjerrig sj\u00e5, vere i k\u00f8. Og vi husker at <code>UPDATE<\/code> vi har ei laaaaang...<br \/>\n<noindex><a rel=\"nofollow\" name=\"habracut\"><\/a><\/noindex><\/p>\n<h4>La oss d\u00e5 sl\u00e5 av raskt, og s\u00e5 sl\u00e5 p\u00e5 igjen raskt!<\/h4>\n<p><\/p>\n<pre><code class=\"sql\">BEGIN;\n  ALTER TABLE ... DISABLE TRIGGER ...;\nCOMMIT;\n\nUPDATE ...;\n\nBEGIN;\n  ALTER TABLE ... ENABLE TRIGGER ...;\nCOMMIT;<\/code><\/pre>\n<p>\nHer er situasjonen mykje betre, ventetida er betydelig kortare. Men det er to problem som \u00f8ydelegg all skj\u00f8nnhet:<\/p>\n<ul>\n<li><code>ALTER TABLE<\/code> den ventar p\u00e5 alle andre operasjonar i tabellen, inkludert lange <code>SELECT<\/code><\/li>\n<li>Mens triggeren er sl\u00e5tt av, <b>\"vil glippe\" alle endringar<\/b> i tabellen, til og med ikkje v\u00e5re. Og dei vil ikkje bli plukka opp i aggregata, sj\u00f8lv om det burde. Forferdeleg!<\/li>\n<\/ul>\n<p><\/p>\n<h2>H\u00e5ndtering av sesjonsvariabler<\/h2>\n<p>\nS\u00e5, i forrige alternativ m\u00f8tte vi eit grunnleggjande poeng \u2014 vi m\u00e5 p\u00e5 ein eller anna m\u00e5te l\u00e6re triggeren \u00e5 skille mellom \"v\u00e5re\" endringar i tabellen og \"ikkje v\u00e5re\". La \"v\u00e5re\" g\u00e5 som dei er, og reager p\u00e5 \"ikkje v\u00e5re\". For dette kan ein bruke <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/runtime-config-client\">sesjonsvariabelar<\/a><\/noindex>.<\/p>\n<h4>session_replication_role<\/h4>\n<p>\nLes <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/sql-altertable\">manualen<\/a><\/noindex>:<\/p>\n<blockquote><p>Den mekanismen for utl\u00f8ysing av triggarar p\u00e5verkas ogs\u00e5 av den konfigurasjonsvariabelen <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/runtime-config-client#GUC-SESSION-REPLICATION-ROLE\">session_replication_role<\/a><\/noindex>. Inkludert utan ekstra instruksjonar (standard) vil triggarar bli utl\u00f8yst n\u00e5r replikasjonsrolla er \"origin\" (standard) eller \"local\". Triggarar som er inkludert med <code>ENABLE REPLICA<\/code>, vil bli utl\u00f8yst berre dersom <b>den noverande sesjonsmodus<\/b> er \"replica\", og triggarar som er inkludert med <code>ENABLE ALWAYS<\/code>, vil bli utl\u00f8yst uavhengig av den noverande replikasjonsmodusen.<\/p><\/blockquote>\n<p>Eg vil spesielt understreke at innstillinga gjelder ikkje alle samtidige, som <code>ALTER TABLE<\/code>, men kun til v\u00e5r separate spesialforbindelse. S\u00e5 for \u00e5 unng\u00e5 at noen applikasjonstriggere utl\u00f8ses:<\/p>\n<pre><code class=\"sql\">SET session_replication_role = replica; -- deaktiverte triggerne\nUPDATE ...;\nSET session_replication_role = DEFAULT; -- tilbake til standardstatus<\/code><\/pre>\n<p><\/p>\n<h4>Betingelsen inne i triggeren<\/h4>\n<p>\nMen alternativet ovenfor fungerer for alle triggerne p\u00e5 en gang (eller m\u00e5 vi \u00abendre\u00bb p\u00e5 forh\u00e5nd de triggerne vi ikke \u00f8nsker \u00e5 deaktivere). Men hvis vi trenger \u00e5 <b>\u00abdeaktivere\u00bb \u00e9n spesifikk trigger<\/b>?<\/p>\n<p>Dette vil hjelpe oss med <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/runtime-config-custom\">\u00abbrukerdefinert\u00bb sesjonsvariabel<\/a><\/noindex>:<\/p>\n<blockquote><p>Navnene p\u00e5 parametrene for utvidelser skrives p\u00e5 f\u00f8lgende m\u00e5te: utvidelsesnavn, punktum og s\u00e5 selve parameterens navn, lik fullstendige objektnavn i SQL. For eksempel: plpgsql.variable_conflict.<br \/>\nSiden ikke-systemparametere kan settes i prosesser som ikke laster den relevante utvidelsesmodulen, godtar PostgreSQL <b>verdier for alle navn med to komponenter<\/b>.<\/p><\/blockquote>\n<p>F\u00f8rst oppdaterer vi triggeren, omtrent slik:<\/p>\n<pre><code class=\"sql\">BEGIN\n    -- prosessen for konvertering kan gj\u00f8re alt\n    IF current_setting('mycfg.my_table_convert_process') = 'TRUE' THEN\n        IF TG_OP IN ('INSERT', 'UPDATE') THEN\n            RETURN NEW;\n        ELSE\n            RETURN OLD;\n        END IF;\n    END IF;\n...<\/code><\/pre>\n<p>\nForresten, dette kan gj\u00f8res \u00ablive\u00bb, uten l\u00e5s, via <code>CREATE OR REPLACE<\/code> for triggerfunksjonen. Og s\u00e5 i spesialforbindelsen setter vi v\u00e5r egen variabel:<\/p>\n<pre><code class=\"sql\">\nSET mycfg.my_table_convert_process = 'TRUE';\nUPDATE ...;\nSET mycfg.my_table_convert_process = ''; -- tilbake til standardstatus\n<\/code><\/pre>\n<p>\nKjenner du andre metoder? Del i kommentarfeltet.<br \/>\n<br \/>Kilde: <a content=\"nofollow\" rel=\"nofollow\" href=\"https:\/\/habr.com\/ru\/company\/tensor\/blog\/489900\/\">habr.com<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"<p>\u0420\u0430\u043d\u043e \u0438\u043b\u0438 \u043f\u043e\u0437\u0434\u043d\u043e \u043c\u043d\u043e\u0433\u0438\u0435 \u0441\u0442\u0430\u043b\u043a\u0438\u0432\u0430\u044e\u0442\u0441\u044f \u0441 \u043d\u0435\u043e\u0431\u0445\u043e\u0434\u0438\u043c\u043e\u0441\u0442\u044c\u044e \u0447\u0442\u043e-\u0442\u043e \u043c\u0430\u0441\u0441\u043e\u0432\u043e \u0438\u0441\u043f\u0440\u0430\u0432\u0438\u0442\u044c \u0432 \u0437\u0430\u043f\u0438\u0441\u044f\u0445 \u0442\u0430\u0431\u043b\u0438\u0446\u044b. \u042f \u0443\u0436\u0435 \u0440\u0430\u0441\u0441\u043a\u0430\u0437\u044b\u0432\u0430\u043b, \u043a\u0430\u043a \u044d\u0442\u043e \u0434\u0435\u043b\u0430\u0442\u044c \u043b\u0443\u0447\u0448\u0435, \u0430 \u043a\u0430\u043a \u2014 \u043b\u0443\u0447\u0448\u0435 \u043d\u0435 \u0434\u0435\u043b\u0430\u0442\u044c. \u0421\u0435\u0433\u043e\u0434\u043d\u044f \u0440\u0430\u0441\u0441\u043a\u0430\u0436\u0443 \u043e \u0432\u0442\u043e\u0440\u043e\u043c \u0430\u0441\u043f\u0435\u043a\u0442\u0435 \u043c\u0430\u0441\u0441\u043e\u0432\u043e\u0433\u043e \u043e\u0431\u043d\u043e\u0432\u043b\u0435\u043d\u0438\u044f \u2014 \u043e \u0441\u0440\u0430\u0431\u043e\u0442\u043a\u0435 \u0442\u0440\u0438\u0433\u0433\u0435\u0440\u043e\u0432. \u041d\u0430\u043f\u0440\u0438\u043c\u0435\u0440, \u043d\u0430 \u0442\u0430\u0431\u043b\u0438\u0446\u0435, \u0432 \u043a\u043e\u0442\u043e\u0440\u043e\u0439 \u0432\u0430\u043c \u043d\u0430\u0434\u043e \u0447\u0442\u043e-\u0442\u043e \u043f\u043e\u043f\u0440\u0430\u0432\u0438\u0442\u044c, \u0432\u0438\u0441\u0438\u0442 \u0437\u043b\u043e\u0431\u043d\u044b\u0439 \u0442\u0440\u0438\u0433\u0433\u0435\u0440 ON UPDATE, \u043f\u0435\u0440\u0435\u043d\u043e\u0441\u044f\u0449\u0438\u0439 \u0432\u0441\u0435 \u0438\u0437\u043c\u0435\u043d\u0435\u043d\u0438\u044f \u0432 [&hellip;]<\/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-72265","post","type-post","status-publish","format-standard","hentry","category-administrirovanie"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 5.0.5 - aioseo.com -->\n\t<meta name=\"description\" content=\"\u0420\u0430\u043d\u043e \u0438\u043b\u0438 \u043f\u043e\u0437\u0434\u043d\u043e \u043c\u043d\u043e\u0433\u0438\u0435 \u0441\u0442\u0430\u043b\u043a\u0438\u0432\u0430\u044e\u0442\u0441\u044f \u0441 \u043d\u0435\u043e\u0431\u0445\u043e\u0434\u0438\u043c\u043e\u0441\u0442\u044c\u044e \u0447\u0442\u043e-\u0442\u043e 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