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Fix some now-obsolete comments about the space used by various data

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types.
This commit is contained in:
Tom Lane 2007-04-06 19:22:38 +00:00
parent e1f1a5358b
commit 146c83c045
2 changed files with 28 additions and 19 deletions
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6
doc/src/sgml/array.sgml
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@ -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>

41
doc/src/sgml/datatype.sgml
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@ -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">