--- /dev/null
+<!-- doc/src/sgml/limits.sgml -->
+
+<appendix id="limits">
+ <title><productname>PostgreSQL</productname> Limits</title>
+
+ <para>
+ <xref linkend="limits-table"/> describes various hard limits of
+ <productname>PostgreSQL</productname>. However, practical limits, such as
+ performance limitations or available disk space may apply before absolute
+ hard limits are reached.
+ </para>
+
+ <table id="limits-table">
+ <title><productname>PostgreSQL</productname> limitations</title>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Item</entry>
+ <entry>Upper Limit</entry>
+ <entry>Comment</entry>
+ </row>
+ </thead>
+
+ <tbody>
+ <row>
+ <entry>database size</entry>
+ <entry>unlimited</entry>
+ <entry></entry>
+ </row>
+
+ <row>
+ <entry>number of databases</entry>
+ <!-- 2^32 - FirstNormalObjectId - 1 -->
+ <entry>4,294,950,911</entry>
+ <entry></entry>
+ </row>
+
+ <row>
+ <entry>relations per database</entry>
+ <!-- (2^32 - FirstNormalObjectId - 1) / 3 (3 because of the table and the
+ two types that are created to go with it) -->
+ <entry>1,431,650,303</entry>
+ <entry></entry>
+ </row>
+
+ <row>
+ <entry>relation size</entry>
+ <entry>32 TB</entry>
+ <entry>with the default <symbol>BLCKSZ</symbol> of 8192 bytes</entry>
+ </row>
+
+ <row>
+ <entry>rows per table</entry>
+ <entry>limited by the number of tuples that can fit onto 4,294,967,295 pages</entry>
+ <entry></entry>
+ </row>
+
+ <row>
+ <entry>columns per table</entry>
+ <entry>1600</entry>
+ <entry>further limited by tuple size fitting on a single page; see note
+ below</entry>
+ </row>
+
+ <row>
+ <entry>field size</entry>
+ <entry>1 GB</entry>
+ <entry></entry>
+ </row>
+
+ <row>
+ <entry>identifier length</entry>
+ <entry>63 bytes</entry>
+ <entry>can be increased by recompiling <productname>PostgreSQL</productname></entry>
+ </row>
+
+ <row>
+ <entry>indexes per table</entry>
+ <entry>unlimited</entry>
+ <entry>constrained by maximum relations per database</entry>
+ </row>
+
+ <row>
+ <entry>columns per index</entry>
+ <entry>32</entry>
+ <entry>can be increased by recompiling <productname>PostgreSQL</productname></entry>
+ </row>
+
+ <row>
+ <entry>partition keys</entry>
+ <entry>32</entry>
+ <entry>can be increased by recompiling <productname>PostgreSQL</productname></entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
+ <para>
+ The maximum number of columns for a table is further reduced as the tuple
+ being stored must fit in a single 8192-byte heap page. For example,
+ excluding the tuple header, a tuple made up of 1600 <type>int</type> columns
+ would consume 6400 bytes and could be stored in a heap page, but a tuple of
+ 1600 <type>bigint</type> columns would consume 12800 bytes and would
+ therefore not fit inside a heap page.
+ Variable-length fields of
+ types such as <type>text</type>, <type>varchar</type>, and <type>char</type>
+ 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.
+ </para>
+
+ <para>
+ Columns that have been dropped from the table also contribute to the maximum
+ column limit. Moreover, although the dropped column values for newly
+ created tuples are internally marked as null in the tuple's null bitmap, the
+ null bitmap also occupies space.
+ </para>
+</appendix>