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diff --git a/doc/src/sgml/limits.sgml b/doc/src/sgml/limits.sgml new file mode 100644 index 0000000..d5b2b62 --- /dev/null +++ b/doc/src/sgml/limits.sgml @@ -0,0 +1,126 @@ +<!-- 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>columns in a result set</entry> + <entry>1664</entry> + <entry></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> |