{"id":10599,"date":"2017-11-02T06:32:28","date_gmt":"2017-11-02T05:32:28","guid":{"rendered":"https:\/\/www.dbi-services.com\/blog\/are-large-objects-supported-in-postgresql-10-logical-replication\/"},"modified":"2017-11-02T06:32:28","modified_gmt":"2017-11-02T05:32:28","slug":"are-large-objects-supported-in-postgresql-10-logical-replication","status":"publish","type":"post","link":"https:\/\/www.dbi-services.com\/blog\/are-large-objects-supported-in-postgresql-10-logical-replication\/","title":{"rendered":"Are large objects supported in PostgreSQL 10 logical replication?"},"content":{"rendered":"<p>Another interesting topic that popped up last week during <a href=\"https:\/\/2017.pgconf.eu\/\" target=\"_blank\" rel=\"noopener\">pgconfeu<\/a>: Are large objects supported with <a href=\"https:\/\/www.postgresql.org\/docs\/current\/static\/logical-replication.html\" target=\"_blank\" rel=\"noopener\">logical replication<\/a> in PostgreSQL 10? The only truth is a test, isn&#8217;t it? Lets go&#8230;<\/p>\n<p><!--more--><\/p>\n<p>Obviously we need a table containing same large objects to start with:<\/p>\n<pre class=\"brush: sql; gutter: true; first-line: 1\">\npostgres=# create table t1 ( a int, b oid);\nCREATE TABLE\n<\/pre>\n<p>Before inserting some data lets create a publication for that table right now:<\/p>\n<pre class=\"brush: sql; gutter: true; first-line: 1\">\npostgres=# create publication my_pub for table t1;\nCREATE PUBLICATION\n<\/pre>\n<p>Ok, that works. Now we need a subscription for that, so on a second instance:<\/p>\n<pre class=\"brush: sql; gutter: true; first-line: 1\">\npostgres=# create table t1 ( a int, b oid);\nCREATE TABLE\npostgres=# create subscription my_sub connection 'host=localhost port=6000 dbname=postgres user=postgres' publication my_pub;\nCREATE SUBSCRIPTION\n<\/pre>\n<p>So far, so good. Lets insert some data on the publishing instance and see what happens:<\/p>\n<pre class=\"brush: sql; gutter: true; first-line: 1\">\npostgres=# ! which cp\n\/usr\/bin\/cp\npostgres=# insert into t1 (a,b) values (1, lo_import('\/usr\/bin\/cp'));\nINSERT 0 1\n<\/pre>\n<p>That worked. What do we see on the subscription side?<\/p>\n<pre class=\"brush: sql; gutter: true; first-line: 1\">\npostgres=# select * from t1;\n a |   b   \n---+-------\n 1 | 16418\n(1 row)\n\npostgres=# select * from pg_size_pretty ( pg_relation_size ( 't1' ) );\n pg_size_pretty \n----------------\n 8192 bytes\n(1 row)\n<\/pre>\n<p>So, at least &#8220;something&#8221; is there. Lets prove it:<\/p>\n<pre class=\"brush: sql; gutter: true; first-line: 1\">\npostgres=# select lo_export(b,'\/tmp\/cp') from t1;\nERROR:  large object 16418 does not exist\npostgres=# \n<\/pre>\n<p>Hm, this is not what was expected, right? Doing the same on the publishing side works:<\/p>\n<pre class=\"brush: sql; gutter: true; first-line: 1\">\npostgres=# select lo_export(b,'\/tmp\/cp') from t1;\n lo_export \n-----------\n         1\n(1 row)\n\npostgres=# ! chmod +x \/tmp\/cp\npostgres=# ! \/tmp\/cp --help | head -1\nUsage: \/tmp\/cp [OPTION]... [-T] SOURCE DEST\n<\/pre>\n<p>This means the OID is replicated but not the large object itself. So the answer is: No, large objects can not be used with PostgreSQL 10 logical replication.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Another interesting topic that popped up last week during pgconfeu: Are large objects supported with logical replication in PostgreSQL 10? The only truth is a test, isn&#8217;t it? Lets go&#8230;<\/p>\n","protected":false},"author":28,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[229],"tags":[77],"type_dbi":[],"class_list":["post-10599","post","type-post","status-publish","format-standard","hentry","category-database-administration-monitoring","tag-postgresql"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v28.8 (Yoast SEO v28.8) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>Are large objects supported in PostgreSQL 10 logical replication? - 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\/are-large-objects-supported-in-postgresql-10-logical-replication\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Are large objects supported in PostgreSQL 10 logical replication?\" \/>\n<meta property=\"og:description\" content=\"Another interesting topic that popped up last week during pgconfeu: Are large objects supported with logical replication in PostgreSQL 10? 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