diff options
| -rw-r--r-- | doc/src/sgml/array.sgml | 6 | ||||
| -rw-r--r-- | doc/src/sgml/datatype.sgml | 41 |
2 files changed, 28 insertions, 19 deletions
diff --git a/doc/src/sgml/array.sgml b/doc/src/sgml/array.sgml index 74e9e083f70..ec59d8e6a88 100644 --- a/doc/src/sgml/array.sgml +++ b/doc/src/sgml/array.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/array.sgml,v 1.59 2007/03/02 06:01:01 tgl Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/array.sgml,v 1.60 2007/04/06 19:22:38 tgl Exp $ --> <sect1 id="arrays"> <title>Arrays</title> @@ -10,8 +10,8 @@ <para> <productname>PostgreSQL</productname> allows columns of a table to be defined as variable-length multidimensional arrays. Arrays of any - built-in or user-defined base type can be created. (Arrays of - composite types or domains are not yet supported, however.) + built-in or user-defined base type or enum type can be created. + (Arrays of composite types or domains are not yet supported, however.) </para> <sect2> diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml index fc5be3a1061..8bcaf717607 100644 --- a/doc/src/sgml/datatype.sgml +++ b/doc/src/sgml/datatype.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.194 2007/04/05 01:46:27 momjian Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.195 2007/04/06 19:22:38 tgl Exp $ --> <chapter id="datatype"> <title id="datatype-title">Data Types</title> @@ -516,7 +516,7 @@ NUMERIC type is more akin to <type>varchar(<replaceable>n</>)</type> than to <type>char(<replaceable>n</>)</type>.) The actual storage requirement is two bytes for each group of four decimal digits, - plus eight bytes overhead. + plus five to eight bytes overhead. </para> <indexterm> @@ -842,9 +842,9 @@ ALTER SEQUENCE <replaceable class="parameter">tablename</replaceable>_<replaceab <tbody> <row> <entry>money</entry> - <entry>4 bytes</entry> + <entry>8 bytes</entry> <entry>currency amount</entry> - <entry>-21474836.48 to +21474836.47</entry> + <entry>-92233720368547758.08 to +92233720368547758.07</entry> </row> </tbody> </tgroup> @@ -975,12 +975,13 @@ ALTER SEQUENCE <replaceable class="parameter">tablename</replaceable>_<replaceab </para> <para> - The storage requirement for data of these types is 4 bytes plus the - actual string, and in case of <type>character</type> plus the - padding. Long strings are compressed by the system automatically, so - the physical requirement on disk might be less. Long values are also - stored in background tables so they do not interfere with rapid - access to the shorter column values. In any case, the longest + The storage requirement for a short string (up to 126 bytes) is 1 byte + plus the actual string, which includes the space padding in the case of + <type>character</type>. Longer strings have 4 bytes overhead instead + of 1. Long strings are compressed by the system automatically, so + the physical requirement on disk might be less. Very long values are also + stored in background tables so that they do not interfere with rapid + access to shorter column values. In any case, the longest possible character string that can be stored is about 1 GB. (The maximum value that will be allowed for <replaceable>n</> in the data type declaration is less than that. It wouldn't be very useful to @@ -994,8 +995,10 @@ ALTER SEQUENCE <replaceable class="parameter">tablename</replaceable>_<replaceab <tip> <para> There are no performance differences between these three types, - apart from the increased storage size when using the blank-padded - type. While <type>character(<replaceable>n</>)</type> has performance + apart from increased storage size when using the blank-padded + type, and a few extra cycles to check the length when storing into + a length-constrained column. While + <type>character(<replaceable>n</>)</type> has performance advantages in some other database systems, it has no such advantages in <productname>PostgreSQL</productname>. In most situations <type>text</type> or <type>character varying</type> should be used @@ -1080,7 +1083,7 @@ SELECT b, char_length(b) FROM test2; <row> <entry><type>"char"</type></entry> <entry>1 byte</entry> - <entry>single-character internal type</entry> + <entry>single-byte internal type</entry> </row> <row> <entry><type>name</type></entry> @@ -1122,7 +1125,7 @@ SELECT b, char_length(b) FROM test2; <tbody> <row> <entry><type>bytea</type></entry> - <entry>4 bytes plus the actual binary string</entry> + <entry>1 or 4 bytes plus the actual binary string</entry> <entry>variable-length binary string</entry> </row> </tbody> @@ -2879,13 +2882,13 @@ SELECT person.name, holidays.num_weeks FROM person, holidays <row> <entry><type>cidr</type></entry> - <entry>12 or 24 bytes</entry> + <entry>7 or 19 bytes</entry> <entry>IPv4 and IPv6 networks</entry> </row> <row> <entry><type>inet</type></entry> - <entry>12 or 24 bytes</entry> + <entry>7 or 19 bytes</entry> <entry>IPv4 and IPv6 hosts and networks</entry> </row> @@ -3188,6 +3191,12 @@ SELECT * FROM test; </programlisting> </example> + <para> + A bit string value requires 1 byte for each group of 8 bits, plus + 5 or 8 bytes overhead depending on the length of the string + (but long values may be compressed or moved out-of-line, as explained + in <xref linkend="datatype-character"> for character strings). + </para> </sect1> <sect1 id="datatype-xml"> |