{"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\/es\/blog\/administrirovanie\/postgresql-antipatterns-menyaem-dannye-v-obhod-triggera","title":{"rendered":"Antipatrones de PostgreSQL: cambiando datos eludiendo el trigger","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p>Tarde o temprano, muchos se enfrentan a la necesidad de realizar correcciones masivas en los registros de una tabla. Ya he <noindex><a rel=\"nofollow\" href=\"https:\/\/habr.com\/post\/481610\/\">hablado sobre c\u00f3mo hacerlo mejor<\/a><\/noindex>, y c\u00f3mo \u2014 mejor no hacerlo. Hoy hablar\u00e9 del segundo aspecto de la actualizaci\u00f3n masiva \u2014 <b>la activaci\u00f3n de disparadores<\/b>.<\/p>\n<p>Por ejemplo, en una tabla donde necesitas corregir algo, hay un agresivo disparador <code>ON UPDATE<\/code>, que transfiere todos los cambios a ciertos agregados. Y necesitas actualizar todo (inicializar un nuevo campo, por ejemplo) de manera tan cuidadosa que estos agregados no sean afectados.<\/p>\n<h2>\u00a1Simplemente desactivemos los disparadores!<\/h2>\n<p><\/p>\n<pre><code class=\"sql\">BEGIN;\n  ALTER TABLE ... DISABLE TRIGGER ...;\n  UPDATE ...; -- aqu\u00ed ser\u00e1 largo\n  ALTER TABLE ... ENABLE TRIGGER ...;\nCOMMIT;<\/code><\/pre>\n<p>\nDe hecho, aqu\u00ed est\u00e1 todo \u2014 <b>todo est\u00e1 en espera<\/b>.<\/p>\n<p>Porque <code>ALTER TABLE<\/code> impone <b>AccessExclusive<\/b>-bloqueo, bajo el cual nadie que est\u00e9 ejecutando algo en paralelo, ni siquiera simple <code>SELECCIONAR<\/code>, podr\u00e1 leer nada de la tabla. Es decir, mientras esta transacci\u00f3n no termine, todos los interesados, incluso solo para \u00ableer\u00bb, tendr\u00e1n que esperar. Y recordamos que <code>ACTUALIZAR<\/code> tenemos un largo\u2026<br \/>\n<noindex><a rel=\"nofollow\" name=\"habracut\"><\/a><\/noindex><\/p>\n<h4>\u00a1Entonces desactivemos r\u00e1pidamente, y luego activemos r\u00e1pidamente!<\/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>\nAqu\u00ed la situaci\u00f3n es ya mejor, el tiempo de espera es considerablemente menor. Pero hay dos problemas que arruinan toda la belleza:<\/p>\n<ul>\n<li><code>ALTER TABLE<\/code> espera todas las dem\u00e1s operaciones en la tabla, incluidas las largas <code>SELECCIONAR<\/code><\/li>\n<li>Mientras el disparador est\u00e1 desactivado, <b>cualquier cambio<\/b> en la tabla, incluso si no es nuestro, \u00abpasar\u00e1 de largo\u00bb. Y no llegar\u00e1 a los agregados, aunque deber\u00eda. \u00a1Problema!<\/li>\n<\/ul>\n<p><\/p>\n<h2>Gesti\u00f3n de variables de sesi\u00f3n<\/h2>\n<p>\nAs\u00ed que, en la variante anterior nos encontramos con un punto fundamental: hay que ense\u00f1ar de alguna manera al disparador a distinguir entre los cambios \u00abnuestros\u00bb y los \u00abno nuestros\u00bb en la tabla. Dejar pasar los \u00abnuestros\u00bb tal como son, y activar para los \u00abno nuestros\u00bb. Para esto, se pueden usar <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/runtime-config-client\">variables de sesi\u00f3n<\/a><\/noindex>.<\/p>\n<h4>session_replication_role<\/h4>\n<p>\nLeamos <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/sql-altertable\">manual<\/a><\/noindex>:<\/p>\n<blockquote><p>El mecanismo de activaci\u00f3n de los disparadores tambi\u00e9n est\u00e1 influenciado por la variable de configuraci\u00f3n <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/runtime-config-client#GUC-SESSION-REPLICATION-ROLE\">session_replication_role<\/a><\/noindex>. Los disparadores habilitados sin instrucciones adicionales (por defecto) se activar\u00e1n cuando el rol de replicaci\u00f3n sea \u00aborigin\u00bb (por defecto) o \u00ablocal\u00bb. Los disparadores habilitados con la especificaci\u00f3n <code>ENABLE REPLICA<\/code>, se activar\u00e1n solo si <b>el modo actual de la sesi\u00f3n<\/b> es \u00abreplica\u00bb, y los disparadores habilitados con la especificaci\u00f3n <code>ENABLE ALWAYS<\/code>, se activar\u00e1n independientemente del modo actual de replicaci\u00f3n.<\/p><\/blockquote>\n<p>Quiero subrayar que esta configuraci\u00f3n no se aplica a todos todos a la vez, como <code>ALTER TABLE<\/code>, sino a nuestra conexi\u00f3n especial. En total, para evitar que se active ning\u00fan trigger aplicado:<\/p>\n<pre><code class=\"sql\">SET session_replication_role = replica; -- desactivamos triggers\nUPDATE ...;\nSET session_replication_role = DEFAULT; -- volvemos al estado original<\/code><\/pre>\n<p><\/p>\n<h4>Condici\u00f3n dentro del trigger<\/h4>\n<p>\nPero la opci\u00f3n anterior funciona para todos los triggers a la vez (o se deben \"alterar\" previamente los triggers que no queremos desactivar). Y si necesitamos <b>\"desactivar\" un trigger espec\u00edfico<\/b>?<\/p>\n<p>Esto nos ayudar\u00e1 <noindex><a rel=\"nofollow\" href=\"https:\/\/postgrespro.ru\/docs\/postgresql\/12\/runtime-config-custom\">\"variable\" de sesi\u00f3n personalizada<\/a><\/noindex>:<\/p>\n<blockquote><p>Los nombres de los par\u00e1metros de las extensiones se escriben de la siguiente manera: nombre de la extensi\u00f3n, punto y luego el nombre del par\u00e1metro, similar a los nombres completos de los objetos en SQL. Por ejemplo: plpgsql.variable_conflict.<br \/>\nDado que los par\u00e1metros no sist\u00e9micos pueden ser establecidos en procesos que no cargan el m\u00f3dulo de extensi\u00f3n correspondiente, PostgreSQL acepta <b>valores para cualquier nombre con dos componentes<\/b>.<\/p><\/blockquote>\n<p>Primero modificamos el trigger, m\u00e1s o menos as\u00ed:<\/p>\n<pre><code class=\"sql\">BEGIN\n    -- el proceso de conversi\u00f3n puede hacer todo\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>\nPor cierto, esto se puede hacer \"en vivo\", sin bloqueos, a trav\u00e9s de <code>CREATE OR REPLACE<\/code> para la funci\u00f3n del trigger. Y luego en la conexi\u00f3n especial configuramos nuestra variable:<\/p>\n<pre><code class=\"sql\">\nSET mycfg.my_table_convert_process = 'TRUE';\nUPDATE ...;\nSET mycfg.my_table_convert_process = ''; -- volvimos al estado original\n<\/code><\/pre>\n<p>\n\u00bfConocen otros m\u00e9todos? Compartan en los comentarios.<br \/>\n<br \/>Fuente: <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 5.0.2 - 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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