{"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\/da\/blog\/administrirovanie\/postgresql-antipatterns-menyaem-dannye-v-obhod-triggera","title":{"rendered":"PostgreSQL Antipatterns: \u00e6ndrer data uden om triggeren","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p>Tidligere eller senere st\u00e5r mange over for behovet for at massere noget i tabellerne. Jeg har allerede <noindex><a rel=\"nofollow\" href=\"https:\/\/habr.com\/post\/481610\/\">fortalt om, hvordan man g\u00f8r det bedst<\/a><\/noindex>, og hvordan det er bedre ikke at g\u00f8re. I dag vil jeg tale om den anden aspekt af masseopdatering \u2014 <b>udf\u00f8relsen af triggere<\/b>.<\/p>\n<p>For eksempel, p\u00e5 en tabel, som du skal \u00e6ndre, er der en ondsindet trigger <code>ON UPDATE<\/code>, der overf\u00f8rer alle \u00e6ndringer til nogle aggregeringer. Og du skal opdatere alt (for at initialisere et nyt felt, for eksempel) s\u00e5 forsigtigt, at disse aggregeringer ikke bliver ber\u00f8rt.<\/p>\n<h2>Lad os bare deaktivere triggerne!<\/h2>\n<p><\/p>\n<pre><code class=\"sql\">BEGIN;\n  ALTER TABLE ... DISABLE TRIGGER ...;\n  UPDATE ...; -- her tager det lang tid\n  ALTER TABLE ... ENABLE TRIGGER ...;\nCOMMIT;<\/code><\/pre>\n<p>\nEgentlig er det det hele \u2014 <b>alt h\u00e6nger allerede<\/b>.<\/p>\n<p>Fordi <code>ALTER TABLE<\/code> p\u00e5virker <b>AccessExclusive<\/b>-l\u00e5sen, under hvilken ingen der k\u00f8rer parallelt, selv en simpel <code>SELECT<\/code>, kan l\u00e6se noget fra tabellen. Det vil sige, s\u00e5 l\u00e6nge denne transaktion ikke er afsluttet, vil alle, der \u00f8nsker at \u00abbare l\u00e6se\u00bb, vente. Og vi husker, at <code>OPDATERING<\/code> vi har en lang\u2026<br \/>\n<noindex><a rel=\"nofollow\" name=\"habracut\"><\/a><\/noindex><\/p>\n<h4>Lad os s\u00e5 hurtigt deaktivere, og s\u00e5 hurtigt aktivere igen!<\/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 situationen allerede bedre, ventetiden er betydeligt kortere. Men to problemer \u00f8del\u00e6gger stadig sk\u00f8nheden:<\/p>\n<ul>\n<li><code>ALTER TABLE<\/code> selv venter p\u00e5 alle andre operationer p\u00e5 tabellen, inklusive lange <code>SELECT<\/code><\/li>\n<li>Mens triggeren er deaktiveret, <b>vil enhver \u00e6ndring<\/b> i tabellen, som vi ikke har foretaget, \u00abflyve forbi\u00bb. Og det vil p\u00e5 ingen m\u00e5de komme ind i aggregeringerne, selvom det burde. Det er et problem!<\/li>\n<\/ul>\n<p><\/p>\n<h2>Styring af sessionens variabler<\/h2>\n<p>\nS\u00e5 i den tidligere variant st\u00f8dte vi p\u00e5 et principielt punkt - vi skal l\u00e6re triggeren at skelne mellem \u00abvores\u00bb \u00e6ndringer i tabellen og \u00abikke vores\u00bb. \u00abVore\u00bb skal passere som de er, og for \u00abikke vores\u00bb - skal den udl\u00f8ses. For dette kan vi bruge <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/runtime-config-client\">sessionens variabler<\/a><\/noindex>.<\/p>\n<h4>session_replication_role<\/h4>\n<p>\nVi l\u00e6ser <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/sql-altertable\">manual<\/a><\/noindex>:<\/p>\n<blockquote><p>Mekanismen for triggerens aktivering p\u00e5virkes ogs\u00e5 af den konfiguration variabel <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/runtime-config-client#GUC-SESSION-REPLICATION-ROLE\">session_replication_role<\/a><\/noindex>. Aktiverede uden yderligere angivelser (som standard) triggere vil aktiveres, n\u00e5r replikationsrollen er \u00aborigin\u00bb (som standard) eller \u00ablocal\u00bb. Triggere aktiveret ved angivelse <code>ENABLE REPLICA<\/code>, vil kun aktiveres, hvis <b>den aktuelle sessionstilstand<\/b> er \u00abreplica\u00bb, og triggere aktiveret ved angivelse <code>ENABLE ALWAYS<\/code>, vil aktiveres uanset den aktuelle replikationsstatus.<\/p><\/blockquote>\n<p>Jeg vil s\u00e6rligt fremh\u00e6ve, at indstillingen ikke g\u00e6lder for alle med det samme, som <code>ALTER TABLE<\/code>, men kun til vores separate specielle forbindelse. I alt, for at undg\u00e5 at nogen anvendte triggere aktiveres:<\/p>\n<pre><code class=\"sql\">SET session_replication_role = replica; -- deaktiverede triggere\nUPDATE ...;\nSET session_replication_role = DEFAULT; -- vendte tilbage til oprindelig tilstand<\/code><\/pre>\n<p><\/p>\n<h4>Betingelsen inde i triggeren<\/h4>\n<p>\nMen den ovenfor n\u00e6vnte metode virker for alle triggere p\u00e5 \u00e9n gang (eller man skal \"\u00e6ndre\" p\u00e5 forh\u00e5nd de triggere, man ikke \u00f8nsker at deaktivere). Og hvad hvis vi skal <b>deaktivere\" en specifik trigger<\/b>?<\/p>\n<p>Dette vil hj\u00e6lpe os med <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/runtime-config-custom\">\"brugerdefineret\" session variabel<\/a><\/noindex>:<\/p>\n<blockquote><p>Navnene p\u00e5 parameterne i udvidelser skrives som f\u00f8lger: navnet p\u00e5 udvidelsen, punktum og derefter selve parameterens navn, ligesom de fulde navne p\u00e5 objekter i SQL. For eksempel: plpgsql.variable_conflict.<br \/>\nDa ikke-system parametre kan indstilles i processer, der ikke indl\u00e6ser den tilsvarende udvidelsesmodul, accepterer PostgreSQL <b>v\u00e6rdier for alle navne med to komponenter<\/b>.<\/p><\/blockquote>\n<p>F\u00f8rst forbedrer vi triggeren, omtrent s\u00e5ledes:<\/p>\n<pre><code class=\"sql\">BEGIN\n    -- process til konvertering kan g\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 g\u00f8res \"live\", uden l\u00e5sninger, via <code>CREATE OR REPLACE<\/code> for triggerfunktionen. Og s\u00e5 aktiverer vi \"vores\" variabel i den specielle forbindelse:<\/p>\n<pre><code class=\"sql\">\nSET mycfg.my_table_convert_process = 'TRUE';\nUPDATE ...;\nSET mycfg.my_table_convert_process = ''; -- vendte tilbage til oprindelig tilstand\n<\/code><\/pre>\n<p>\nKender du andre m\u00e5der? Del venligst i kommentarerne.<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 5.0.3 - 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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