{"id":37469,"date":"2025-02-28T10:36:34","date_gmt":"2025-02-28T09:36:34","guid":{"rendered":"https:\/\/www.dbi-services.com\/blog\/?p=37469"},"modified":"2025-02-28T10:36:42","modified_gmt":"2025-02-28T09:36:42","slug":"postgresql-unlogged-tables-and-backups","status":"publish","type":"post","link":"https:\/\/www.dbi-services.com\/blog\/postgresql-unlogged-tables-and-backups\/","title":{"rendered":"PostgreSQL: Unlogged tables and backups"},"content":{"rendered":"\n<p>Recently we faced the following situation and have been asked to analyze the issue: A dump was loaded into a primary instance of PostgreSQL, but the data did not reach the replica. Tables which have been added after the dump was loaded, however made it to the replica. After going through the logs it quickly became clear that the reason for this was, that the tables were create as unlogged.<\/p>\n\n\n\n<p>To demonstrate what happens in that case we can easily create a simple test case:<\/p>\n\n\n<div class=\"wp-block-syntaxhighlighter-code \"><pre class=\"brush: sql; highlight: [1,3,5]; title: ; notranslate\" title=\"\">\npostgres=# create unlogged table t ( a int );\nCREATE TABLE\npostgres=# insert into t select * from generate_series(1,1000000);\nINSERT 0 1000000\npostgres=# select count(*) from t;\n  count  \n---------\n 1000000\n(1 row)\n<\/pre><\/div>\n\n\n<p>This is one simple unlogged table containing one million row. Let&#8217;s create a backup of that and start a new instance from that backup:<\/p>\n\n\n<div class=\"wp-block-syntaxhighlighter-code \"><pre class=\"brush: bash; highlight: [1,2,3,4,5]; title: ; notranslate\" title=\"\">\npostgres@pgbox:\/home\/postgres\/ &#x5B;pgdev] mkdir \/var\/tmp\/xx\npostgres@pgbox:\/home\/postgres\/ &#x5B;pgdev] pg_basebackup --checkpoint=fast --pgdata=\/var\/tmp\/xx\npostgres@pgbox:\/home\/postgres\/ &#x5B;pgdev] echo &quot;port=8888&quot; &gt;&gt; \/var\/tmp\/xx\/postgresql.auto.conf\npostgres@pgbox:\/home\/postgres\/ &#x5B;pgdev] chmod 700 \/var\/tmp\/xx\/\npostgres@pgbox:\/home\/postgres\/ &#x5B;pgdev] pg_ctl --pgdata=\/var\/tmp\/xx\/ start\n<\/pre><\/div>\n\n\n<p>Now we have a new instance which should be an exact copy of the source instance. The surprise comes once we check the table we&#8217;ve created:<\/p>\n\n\n<div class=\"wp-block-syntaxhighlighter-code \"><pre class=\"brush: sql; highlight: [1,5]; title: ; notranslate\" title=\"\">\npostgres@pgbox:\/home\/postgres\/ &#x5B;pgdev] psql -p 8888\npsql (18devel)\nType &quot;help&quot; for help.\n\npostgres=# select count(*) from t;\n count \n-------\n     0\n(1 row)\n<\/pre><\/div>\n\n\n<p>The table is there, but it does not contain any rows. Exactly the same happens when you have a replica. This is also clearly stated in the <a href=\"https:\/\/www.postgresql.org\/docs\/17\/sql-createtable.html#SQL-CREATETABLE-UNLOGGED\" target=\"_blank\" rel=\"noreferrer noopener\">documentation<\/a>. When you go for unlogged tables, you must be aware of the consequences. If you skip WAL logging this makes those tables faster than ordinary tables, but this also comes with downsides.<\/p>\n\n\n\n<p>If you dump those tables, you&#8217;ll have the data:<\/p>\n\n\n<div class=\"wp-block-syntaxhighlighter-code \"><pre class=\"brush: bash; title: ; notranslate\" title=\"\">\npostgres@pgbox:\/home\/postgres\/ &#x5B;pgdev] pg_dump &gt; a.sql\npostgres@pgbox:\/home\/postgres\/ &#x5B;pgdev] grep -A 2 COPY a.sql \nCOPY public.t (a) FROM stdin;\n1\n2\n<\/pre><\/div>\n\n\n<p>But please keep in mind: A dump is not a real backup and you cannot use it for point in time recovery.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Recently we faced the following situation and have been asked to analyze the issue: A dump was loaded into a primary instance of PostgreSQL, but the data did not reach the replica. Tables which have been added after the dump was loaded, however made it to the replica. After going through the logs it quickly [&hellip;]<\/p>\n","protected":false},"author":29,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[229,198],"tags":[77],"type_dbi":[],"class_list":["post-37469","post","type-post","status-publish","format-standard","hentry","category-database-administration-monitoring","category-database-management","tag-postgresql"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v27.2 (Yoast SEO v27.2) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>PostgreSQL: Unlogged tables and backups - dbi Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.dbi-services.com\/blog\/postgresql-unlogged-tables-and-backups\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"PostgreSQL: Unlogged tables and backups\" \/>\n<meta property=\"og:description\" content=\"Recently we faced the following situation and have been asked to analyze the issue: A dump was loaded into a primary instance of PostgreSQL, but the data did not reach the replica. 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After going through the logs it quickly [&hellip;]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.dbi-services.com\/blog\/postgresql-unlogged-tables-and-backups\/\" \/>\n<meta property=\"og:site_name\" content=\"dbi Blog\" \/>\n<meta property=\"article:published_time\" content=\"2025-02-28T09:36:34+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2025-02-28T09:36:42+00:00\" \/>\n<meta name=\"author\" content=\"Daniel Westermann\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:creator\" content=\"@westermanndanie\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Daniel Westermann\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"1 minute\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\/\/www.dbi-services.com\/blog\/postgresql-unlogged-tables-and-backups\/#article\",\"isPartOf\":{\"@id\":\"https:\/\/www.dbi-services.com\/blog\/postgresql-unlogged-tables-and-backups\/\"},\"author\":{\"name\":\"Daniel Westermann\",\"@id\":\"https:\/\/www.dbi-services.com\/blog\/#\/schema\/person\/8d08e9bd996a89bd75c0286cbabf3c66\"},\"headline\":\"PostgreSQL: Unlogged tables and backups\",\"datePublished\":\"2025-02-28T09:36:34+00:00\",\"dateModified\":\"2025-02-28T09:36:42+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\/\/www.dbi-services.com\/blog\/postgresql-unlogged-tables-and-backups\/\"},\"wordCount\":234,\"commentCount\":0,\"keywords\":[\"PostgreSQL\"],\"articleSection\":[\"Database Administration &amp; Monitoring\",\"Database management\"],\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"CommentAction\",\"name\":\"Comment\",\"target\":[\"https:\/\/www.dbi-services.com\/blog\/postgresql-unlogged-tables-and-backups\/#respond\"]}]},{\"@type\":\"WebPage\",\"@id\":\"https:\/\/www.dbi-services.com\/blog\/postgresql-unlogged-tables-and-backups\/\",\"url\":\"https:\/\/www.dbi-services.com\/blog\/postgresql-unlogged-tables-and-backups\/\",\"name\":\"PostgreSQL: Unlogged tables and backups - dbi Blog\",\"isPartOf\":{\"@id\":\"https:\/\/www.dbi-services.com\/blog\/#website\"},\"datePublished\":\"2025-02-28T09:36:34+00:00\",\"dateModified\":\"2025-02-28T09:36:42+00:00\",\"author\":{\"@id\":\"https:\/\/www.dbi-services.com\/blog\/#\/schema\/person\/8d08e9bd996a89bd75c0286cbabf3c66\"},\"breadcrumb\":{\"@id\":\"https:\/\/www.dbi-services.com\/blog\/postgresql-unlogged-tables-and-backups\/#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\/\/www.dbi-services.com\/blog\/postgresql-unlogged-tables-and-backups\/\"]}]},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\/\/www.dbi-services.com\/blog\/postgresql-unlogged-tables-and-backups\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Accueil\",\"item\":\"https:\/\/www.dbi-services.com\/blog\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"PostgreSQL: Unlogged tables and backups\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\/\/www.dbi-services.com\/blog\/#website\",\"url\":\"https:\/\/www.dbi-services.com\/blog\/\",\"name\":\"dbi Blog\",\"description\":\"\",\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\/\/www.dbi-services.com\/blog\/?s={search_term_string}\"},\"query-input\":{\"@type\":\"PropertyValueSpecification\",\"valueRequired\":true,\"valueName\":\"search_term_string\"}}],\"inLanguage\":\"en-US\"},{\"@type\":\"Person\",\"@id\":\"https:\/\/www.dbi-services.com\/blog\/#\/schema\/person\/8d08e9bd996a89bd75c0286cbabf3c66\",\"name\":\"Daniel Westermann\",\"image\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\/\/secure.gravatar.com\/avatar\/31350ceeecb1dd8986339a29bf040d4cd3cd087d410deccd8f55234466d6c317?s=96&d=mm&r=g\",\"url\":\"https:\/\/secure.gravatar.com\/avatar\/31350ceeecb1dd8986339a29bf040d4cd3cd087d410deccd8f55234466d6c317?s=96&d=mm&r=g\",\"contentUrl\":\"https:\/\/secure.gravatar.com\/avatar\/31350ceeecb1dd8986339a29bf040d4cd3cd087d410deccd8f55234466d6c317?s=96&d=mm&r=g\",\"caption\":\"Daniel Westermann\"},\"description\":\"Daniel Westermann is Principal Consultant and Technology Leader Open Infrastructure at dbi services. He has more than 15 years of experience in management, engineering and optimization of databases and infrastructures, especially on Oracle and PostgreSQL. Since the beginning of his career, he has specialized in Oracle Technologies and is Oracle Certified Professional 12c and Oracle Certified Expert RAC\/GridInfra. Over time, Daniel has become increasingly interested in open source technologies, becoming \u201cTechnology Leader Open Infrastructure\u201d and PostgreSQL expert. \u00a0Based on community or EnterpriseDB tools, he develops and installs complex high available solutions with PostgreSQL. He is also a certified PostgreSQL Plus 9.0 Professional and a Postgres Advanced Server 9.4 Professional. He is a regular speaker at PostgreSQL conferences in Switzerland and Europe. Today Daniel is also supporting our customers on AWS services such as AWS RDS, database migrations into the cloud, EC2 and automated infrastructure management with AWS SSM (System Manager). 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His branch-related experience mainly covers the pharma industry, the financial sector, energy, lottery and telecommunications.\",\"sameAs\":[\"https:\/\/x.com\/westermanndanie\"],\"url\":\"https:\/\/www.dbi-services.com\/blog\/author\/daniel-westermann\/\"}]}<\/script>\n<!-- \/ Yoast SEO Premium plugin. -->","yoast_head_json":{"title":"PostgreSQL: Unlogged tables and backups - dbi Blog","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.dbi-services.com\/blog\/postgresql-unlogged-tables-and-backups\/","og_locale":"en_US","og_type":"article","og_title":"PostgreSQL: Unlogged tables and backups","og_description":"Recently we faced the following situation and have been asked to analyze the issue: A dump was loaded into a primary instance of PostgreSQL, but the data did not reach the replica. 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He has more than 15 years of experience in management, engineering and optimization of databases and infrastructures, especially on Oracle and PostgreSQL. Since the beginning of his career, he has specialized in Oracle Technologies and is Oracle Certified Professional 12c and Oracle Certified Expert RAC\/GridInfra. Over time, Daniel has become increasingly interested in open source technologies, becoming \u201cTechnology Leader Open Infrastructure\u201d and PostgreSQL expert. \u00a0Based on community or EnterpriseDB tools, he develops and installs complex high available solutions with PostgreSQL. He is also a certified PostgreSQL Plus 9.0 Professional and a Postgres Advanced Server 9.4 Professional. He is a regular speaker at PostgreSQL conferences in Switzerland and Europe. Today Daniel is also supporting our customers on AWS services such as AWS RDS, database migrations into the cloud, EC2 and automated infrastructure management with AWS SSM (System Manager). 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