{"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\/sv\/blog\/administrirovanie\/postgresql-antipatterns-menyaem-dannye-v-obhod-triggera","title":{"rendered":"PostgreSQL Antipatterns: vi \u00e4ndrar data omv\u00e4gen f\u00f6r trigger","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p>F\u00f6rr eller senare st\u00f6ter m\u00e5nga p\u00e5 n\u00f6dv\u00e4ndigheten av att mass\u00e4ndra poster i en tabell. Jag har redan <noindex><a rel=\"nofollow\" href=\"https:\/\/habr.com\/post\/481610\/\">ber\u00e4ttat hur man g\u00f6r det b\u00e4ttre<\/a><\/noindex>, och hur man \u2014 hellre inte g\u00f6r det. Idag kommer jag att prata om den andra aspekten av massuppdatering \u2014 <b>om triggers<\/b>.<\/p>\n<p>Till exempel, i en tabell d\u00e4r du beh\u00f6ver \u00e4ndra n\u00e5got, h\u00e4nger det en elak trigger <code>ON UPDATE<\/code>, som flyttar alla \u00e4ndringar till olika aggregat. Och du vill uppdatera allt (initiera ett nytt f\u00e4lt, till exempel) s\u00e5 f\u00f6rsiktigt att dessa aggregat inte p\u00e5verkas.<\/p>\n<h2>L\u00e5t oss bara st\u00e4nga av triggerna!<\/h2>\n<p><\/p>\n<pre><code class=\"sql\">BEGIN;\n  ALTER TABLE ... DISABLE TRIGGER ...;\n  UPDATE ...; -- h\u00e4r tar det l\u00e5ng tid\n  ALTER TABLE ... ENABLE TRIGGER ...;\nCOMMIT;<\/code><\/pre>\n<p>\nEgentligen \u00e4r det allt \u2014 <b>allt h\u00e4nger redan<\/b>.<\/p>\n<p>F\u00f6r att <code>ALTER TABLE<\/code> det l\u00e4gger p\u00e5 <b>AccessExclusive<\/b>-l\u00e5sning, vilket inneb\u00e4r att ingen process som k\u00f6rs parallellt, inte ens en enkel <code>V\u00c4LJ<\/code>, kan l\u00e4sa n\u00e5got fr\u00e5n tabellen. Det vill s\u00e4ga, s\u00e5 l\u00e4nge denna transaktion inte \u00e4r avslutad, kommer alla som vill \"bara l\u00e4sa\" att v\u00e4nta. Och vi minns att <code>UPPDATERA<\/code> vi har en la-a-ang tid\u2026<br \/>\n<noindex><a rel=\"nofollow\" name=\"habracut\"><\/a><\/noindex><\/p>\n<h4>L\u00e5t oss d\u00e5 snabbt st\u00e4nga av den, sen snabbt sl\u00e5 p\u00e5 den 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>\nH\u00e4r \u00e4r situationen redan b\u00e4ttre, v\u00e4ntetiden \u00e4r avsev\u00e4rt mindre. Men tv\u00e5 problem f\u00f6rst\u00f6r hela sk\u00f6nheten:<\/p>\n<ul>\n<li><code>ALTER TABLE<\/code> sj\u00e4lva v\u00e4ntar p\u00e5 alla andra operationer p\u00e5 tabellen, inklusive de l\u00e5nga <code>V\u00c4LJ<\/code><\/li>\n<li>S\u00e5 l\u00e4nge triggern \u00e4r avst\u00e4ngd, <b>\"flyger f\u00f6rbi\" varje f\u00f6r\u00e4ndring<\/b> i tabellen, \u00e4ven om det inte \u00e4r v\u00e5rt. Och i aggregaten kommer det p\u00e5 inget s\u00e4tt att hamna, \u00e4ven om det borde. M\u00e5let!<\/li>\n<\/ul>\n<p><\/p>\n<h2>Hantera sessionvariabler<\/h2>\n<p>\nS\u00e5, i den f\u00f6reg\u00e5ende varianten st\u00f6ter vi p\u00e5 en principiell punkt \u2014 vi m\u00e5ste p\u00e5 n\u00e5got s\u00e4tt l\u00e4ra triggern att s\u00e4rskilja \"v\u00e5ra\" \u00e4ndringar i tabellen fr\u00e5n \"inte v\u00e5ra\". \"V\u00e5ra\" ska passera som de \u00e4r, och f\u00f6r \"inte v\u00e5ra\" \u2014 trigga. F\u00f6r detta kan vi anv\u00e4nda <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/runtime-config-client\">sessionvariabler<\/a><\/noindex>.<\/p>\n<h4>session_replication_role<\/h4>\n<p>\nVi l\u00e4ser <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/sql-altertable\">manual<\/a><\/noindex>:<\/p>\n<blockquote><p>Mekanismen f\u00f6r triggeraktivering p\u00e5verkas ocks\u00e5 av konfigurationsvariabeln <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/runtime-config-client#GUC-SESSION-REPLICATION-ROLE\">session_replication_role<\/a><\/noindex>. Aktiverade utan ytterligare instruktioner (standard) kommer triggers att aktiveras n\u00e4r replikeringsrollen \u00e4r - \"origin\" (standard) eller \"local\". Triggers som aktiveras genom att ange <code>ENABLE REPLICA<\/code>, aktiveras bara om <b>den aktuella sessionsl\u00e4get<\/b> \u00e4r - \"replica\", medan triggers som aktiveras genom att ange <code>ENABLE ALWAYS<\/code>, kommer att aktiveras oavsett det aktuella replikeringsl\u00e4get.<\/p><\/blockquote>\n<p>Jag betonar s\u00e4rskilt att inst\u00e4llningen g\u00e4ller inte f\u00f6r alla direkt, som <code>ALTER TABLE<\/code>, men bara till v\u00e5r separata specialkoppling. S\u00e5ledes, f\u00f6r att inga applikationstriggare ska aktiveras:<\/p>\n<pre><code class=\"sql\">SET session_replication_role = replica; -- st\u00e4ngde av triggare\nUPDATE ...;\nSET session_replication_role = DEFAULT; -- \u00e5terst\u00e4llning till ursprungligt tillst\u00e5nd<\/code><\/pre>\n<p><\/p>\n<h4>Villkoret inom triggar<\/h4>\n<p>\nMen det ovanst\u00e5ende alternativet fungerar f\u00f6r alla triggare samtidigt (eller m\u00e5ste vi \"alterera\" i f\u00f6rv\u00e4g de triggare vi inte vill st\u00e4nga av). Och om vi beh\u00f6ver <b>st\u00e4nga av\" en specifik trigger<\/b>?<\/p>\n<p>Det h\u00e4r hj\u00e4lper oss med <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/runtime-config-custom\">\"anpassad\" sessionsvariabel<\/a><\/noindex>:<\/p>\n<blockquote><p>Namn p\u00e5 parameterar i till\u00e4gg skrivs p\u00e5 f\u00f6ljande s\u00e4tt: till\u00e4ggens namn, punkt och sedan sj\u00e4lva parameterens namn, liknande fullst\u00e4ndiga objektnamn i SQL. Till exempel: plpgsql.variable_conflict.<br \/>\nEftersom externa parametrar kan st\u00e4llas in i processer som inte laddar motsvarande till\u00e4ggsmodul, accepterar PostgreSQL <b>v\u00e4rden f\u00f6r alla namn med tv\u00e5 komponenter<\/b>.<\/p><\/blockquote>\n<p>F\u00f6rst justerar vi triggar, ungef\u00e4r s\u00e5 h\u00e4r:<\/p>\n<pre><code class=\"sql\">BEGIN\n    -- omvandlingsprocessen kan g\u00f6ra allt\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>\nF\u00f6rresten, detta kan g\u00f6ras \"live\", utan l\u00e5sning, genom <code>CREATE OR REPLACE<\/code> f\u00f6r triggerfunktionen. Och sedan st\u00e4ller vi in \"v\u00e5r\" variabel i specialkopplingen:<\/p>\n<pre><code class=\"sql\">\nSET mycfg.my_table_convert_process = 'TRUE';\nUPDATE ...;\nSET mycfg.my_table_convert_process = ''; -- \u00e5terst\u00e4llning till ursprungligt tillst\u00e5nd\n<\/code><\/pre>\n<p>\nK\u00e4nner du till andra s\u00e4tt? Dela med dig i kommentarerna.<br \/>\n<br \/>K\u00e4lla: <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 5.0.4 - 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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