From 61677219e197e71ed1a487a4dd6c2e46cdc47fd2 Mon Sep 17 00:00:00 2001 From: "dgrowley@gmail.com" Date: Wed, 31 Oct 2018 01:45:41 +1300 Subject: [PATCH v5] Add documentation section appendix detailing some limitations of PostgreSQL --- doc/src/sgml/filelist.sgml | 1 + doc/src/sgml/limits.sgml | 128 +++++++++++++++++++++++++++++++++++++++++++++ doc/src/sgml/postgres.sgml | 1 + 3 files changed, 130 insertions(+) create mode 100644 doc/src/sgml/limits.sgml diff --git a/doc/src/sgml/filelist.sgml b/doc/src/sgml/filelist.sgml index 48ac14a838..0cf8960b8b 100644 --- a/doc/src/sgml/filelist.sgml +++ b/doc/src/sgml/filelist.sgml @@ -184,6 +184,7 @@ + diff --git a/doc/src/sgml/limits.sgml b/doc/src/sgml/limits.sgml new file mode 100644 index 0000000000..09b7348092 --- /dev/null +++ b/doc/src/sgml/limits.sgml @@ -0,0 +1,128 @@ + + + + <productname>PostgreSQL</productname> Limitations + + + Practical limits, such as performance limitations or available disk space + may apply before absolute hard limits are reached. However, with those + aside, the following table describes the hard limits of + PostgreSQL. + + + + <productname>PostgreSQL</productname> limitations + + + + Item + Upper Limit + Comment + + + + + + Database size + Unlimited + + + + + Number of databases + + 4,294,950,911 + + + + + Relations per database + + 1,431,650,303 + + + + + Relation size + 32 TB + Assuming the default BLCKSZ of 8192 bytes + + + + Rows per table + Limited by the number of tuples that can fit onto 4,294,967,295 pages + + + + + Columns per table + 1600 + Further limited by tuple size fitting on a single page. See note + below + + + + Field size + 1 GB + + + + + Identifier length + 63 bytes + Can be increased by recompiling + PostgreSQL + + + + Indexes per table + Unlimited + Constrained by maximum relations per database + + + + Columns per index + 32 + Can be increased by recompiling + PostgreSQL + + + + Partition keys + 32 + Can be increased by recompiling + PostgreSQL + + + +
+ + + + The maximum number of columns for a table is further reduced as the tuple + being stored must fit on a single heap page. Variable length fields such + as TEXT, VARCHAR and + CHAR can have their values stored out of line in the + table's TOAST table when the values are large enough to require it. Only + an 18 byte pointer must remain inside the tuple in the table's heap. For + shorter length variable length fields either a 4 byte or 1 byte field + header is used, and the value is stored inside the heap tuple. Often + this can mean the actual maximum number of columns that you can store + inside a table is further reduced as the tuple can become too large to + fit inside a single 8192 byte heap page. For example, excluding the + tuple header, a tuple made up of 1600 INT columns + would consume 6400 bytes and could be stored in a heap page, but a tuple + of 1600 BIGINT columns would consume 12800 bytes, + therefore not fit inside a heap page. + + + + Columns which have been dropped from the table also contribute to the + maximum column limit, although the dropped column values for newly + created tuples are internally marked as NULL in the tuple's null bitmap, + which does occupy space. + + + + diff --git a/doc/src/sgml/postgres.sgml b/doc/src/sgml/postgres.sgml index 0070603fc3..2fe6f9ca42 100644 --- a/doc/src/sgml/postgres.sgml +++ b/doc/src/sgml/postgres.sgml @@ -276,6 +276,7 @@ &external-projects; &sourcerepo; &docguide; + &limits; &acronyms; -- 2.16.2.windows.1