{"id":15326,"date":"2020-11-30T07:36:49","date_gmt":"2020-11-30T06:36:49","guid":{"rendered":"https:\/\/www.dbi-services.com\/blog\/postgresql-14-automatic-hash-and-list-partitioning\/"},"modified":"2020-11-30T07:36:49","modified_gmt":"2020-11-30T06:36:49","slug":"postgresql-14-automatic-hash-and-list-partitioning","status":"publish","type":"post","link":"https:\/\/www.dbi-services.com\/blog\/postgresql-14-automatic-hash-and-list-partitioning\/","title":{"rendered":"PostgreSQL 14: Automatic hash and list partitioning?"},"content":{"rendered":"<p>Declarative partitioning was introduced in <a href=\"https:\/\/www.postgresql.org\/docs\/10\/ddl-partitioning.html\" target=\"_blank\" rel=\"noopener noreferrer\">PostgreSQL 10<\/a> and since then has improved quite much over the last releases. Today almost everything is there what you would expect from such a feature:<\/p>\n<ul>\n<li>You can partition by range, list and hash<\/li>\n<li>Attaching and detaching partitions<\/li>\n<li>Foreign keys<\/li>\n<li>Sub-partitioning<\/li>\n<li>Indexing and constrains on partitions<\/li>\n<li>Partition pruning<\/li>\n<\/ul>\n<p>What is missing, is the possibility to let PostgreSQL create partitions automatically. With <a href=\"https:\/\/www.postgresql.org\/message-id\/flat\/7fec3abb-c663-c0d2-8452-a46141be6d4a%40postgrespro.ru\" target=\"_blank\" rel=\"noopener noreferrer\">this patch<\/a> this will finally be possible for hash and list partitioning, once it gets committed.<\/p>\n<p><!--more--><\/p>\n<p>Lets start with list partitioning: Looking at the patch, new syntax is introduced:<\/p>\n<pre class=\"brush: sql; gutter: true; first-line: 1\">\nCREATE TABLE tbl_list (i int) PARTITION BY LIST (i)\nCONFIGURATION (values in (1, 2), (3, 4) DEFAULT PARTITION tbl_default);\n<\/pre>\n<p>Taking that as an example we should see all partitions created automatically, if we create a partitioned table like this:<\/p>\n<pre class=\"brush: sql; gutter: true; first-line: 1\">\npostgres=# create table tpart_list ( a text primary key, b int, c int )\n           partition by list(a)\n           configuration (values in ('a'),('b'),('c'),('d') default partition tpart_list_default);\nCREATE TABLE\n<\/pre>\n<p>That should have created 5 partitions automatically: a,b,c,d and the default partition:<\/p>\n<pre class=\"brush: sql; gutter: true; first-line: 1\">\npostgres=# d+ tpart_list\n                           Partitioned table \"public.tpart_list\"\n Column |  Type   | Collation | Nullable | Default | Storage  | Stats target | Description \n--------+---------+-----------+----------+---------+----------+--------------+-------------\n a      | text    |           | not null |         | extended |              | \n b      | integer |           |          |         | plain    |              | \n c      | integer |           |          |         | plain    |              | \nPartition key: LIST (a)\nIndexes:\n    \"tpart_list_pkey\" PRIMARY KEY, btree (a)\nPartitions: tpart_list_0 FOR VALUES IN ('a'),\n            tpart_list_1 FOR VALUES IN ('b'),\n            tpart_list_2 FOR VALUES IN ('c'),\n            tpart_list_3 FOR VALUES IN ('d'),\n            tpart_list_default DEFAULT\n<\/pre>\n<p>Nice. The same works for hash partitioned tables but the syntax is slightly different:<\/p>\n<pre class=\"brush: sql; gutter: true; first-line: 1\">\nCREATE TABLE tbl_hash (i int) PARTITION BY HASH (i)\nCONFIGURATION (modulus 3);\n<\/pre>\n<p>The idea is the same, of course: You need to specify the &#8220;configuration&#8221; and when you go for hash partitioning you need to provide the modulus:<\/p>\n<pre class=\"brush: sql; gutter: true; first-line: 1\">\npostgres=# create table tpart_hash ( a int primary key, b text)\n           partition by hash (a)\n           configuration (modulus 5);\nCREATE TABLE\npostgres=# d+ tpart_hash\n                           Partitioned table \"public.tpart_hash\"\n Column |  Type   | Collation | Nullable | Default | Storage  | Stats target | Description \n--------+---------+-----------+----------+---------+----------+--------------+-------------\n a      | integer |           | not null |         | plain    |              | \n b      | text    |           |          |         | extended |              | \nPartition key: HASH (a)\nIndexes:\n    \"tpart_hash_pkey\" PRIMARY KEY, btree (a)\nPartitions: tpart_hash_0 FOR VALUES WITH (modulus 5, remainder 0),\n            tpart_hash_1 FOR VALUES WITH (modulus 5, remainder 1),\n            tpart_hash_2 FOR VALUES WITH (modulus 5, remainder 2),\n            tpart_hash_3 FOR VALUES WITH (modulus 5, remainder 3),\n            tpart_hash_4 FOR VALUES WITH (modulus 5, remainder 4)\n<\/pre>\n<p>Really nice, great work and thanks to all involved. I hope that the next steps will be:<\/p>\n<ul>\n<li>Support automatic partition creation for range partitioning<\/li>\n<li>Support automatic partition creation on the fly when data comes in, which requires a new partition. In the thread this is referenced as &#8220;dynamic&#8221; partitioning and what is implemented here is referenced as &#8220;static&#8221; partitioning<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Declarative partitioning was introduced in PostgreSQL 10 and since then has improved quite much over the last releases. Today almost everything is there what you would expect from such a feature: You can partition by range, list and hash Attaching and detaching partitions Foreign keys Sub-partitioning Indexing and constrains on partitions Partition pruning What is [&hellip;]<\/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-15326","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>PostgreSQL 14: Automatic hash and list partitioning? - 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-14-automatic-hash-and-list-partitioning\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"PostgreSQL 14: Automatic hash and list partitioning?\" \/>\n<meta property=\"og:description\" content=\"Declarative partitioning was introduced in PostgreSQL 10 and since then has improved quite much over the last releases. 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