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Commit146c83c

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committed
Fix some now-obsolete comments about the space used by various data
types.
1 parente1f1a53 commit146c83c

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2 files changed

+28
-19
lines changed

2 files changed

+28
-19
lines changed

‎doc/src/sgml/array.sgml‎

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
1-
<!-- $PostgreSQL: pgsql/doc/src/sgml/array.sgml,v 1.59 2007/03/02 06:01:01 tgl Exp $ -->
1+
<!-- $PostgreSQL: pgsql/doc/src/sgml/array.sgml,v 1.60 2007/04/06 19:22:38 tgl Exp $ -->
22

33
<sect1 id="arrays">
44
<title>Arrays</title>
@@ -10,8 +10,8 @@
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<para>
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<productname>PostgreSQL</productname> allows columns of a table to be
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defined as variable-length multidimensional arrays. Arrays of any
13-
built-in or user-defined base type can be created. (Arrays of
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composite types or domains are not yet supported, however.)
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built-in or user-defined base typeor enum typecan be created.
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(Arrays ofcomposite types or domains are not yet supported, however.)
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</para>
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<sect2>

‎doc/src/sgml/datatype.sgml‎

Lines changed: 25 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
1-
<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.194 2007/04/05 01:46:27 momjian Exp $ -->
1+
<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.195 2007/04/06 19:22:38 tgl Exp $ -->
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33
<chapter id="datatype">
44
<title id="datatype-title">Data Types</title>
@@ -516,7 +516,7 @@ NUMERIC
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type is more akin to <type>varchar(<replaceable>n</>)</type>
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than to <type>char(<replaceable>n</>)</type>.) The actual storage
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requirement is two bytes for each group of four decimal digits,
519-
plus eight bytes overhead.
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plusfive toeight bytes overhead.
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</para>
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<indexterm>
@@ -842,9 +842,9 @@ ALTER SEQUENCE <replaceable class="parameter">tablename</replaceable>_<replaceab
842842
<tbody>
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<row>
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<entry>money</entry>
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<entry>4 bytes</entry>
845+
<entry>8 bytes</entry>
846846
<entry>currency amount</entry>
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<entry>-21474836.48 to +21474836.47</entry>
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<entry>-92233720368547758.08 to +92233720368547758.07</entry>
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</row>
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</tbody>
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</tgroup>
@@ -975,12 +975,13 @@ ALTER SEQUENCE <replaceable class="parameter">tablename</replaceable>_<replaceab
975975
</para>
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977977
<para>
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The storage requirement for data of these types is 4 bytes plus the
979-
actual string, and in case of <type>character</type> plus the
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padding. Long strings are compressed by the system automatically, so
981-
the physical requirement on disk might be less. Long values are also
982-
stored in background tables so they do not interfere with rapid
983-
access to the shorter column values. In any case, the longest
978+
The storage requirement for a short string (up to 126 bytes) is 1 byte
979+
plus the actual string, which includes the space padding in the case of
980+
<type>character</type>. Longer strings have 4 bytes overhead instead
981+
of 1. Long strings are compressed by the system automatically, so
982+
the physical requirement on disk might be less. Very long values are also
983+
stored in background tables so that they do not interfere with rapid
984+
access to shorter column values. In any case, the longest
984985
possible character string that can be stored is about 1 GB. (The
985986
maximum value that will be allowed for <replaceable>n</> in the data
986987
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
994995
<tip>
995996
<para>
996997
There are no performance differences between these three types,
997-
apart from the increased storage size when using the blank-padded
998-
type. While <type>character(<replaceable>n</>)</type> has performance
998+
apart from increased storage size when using the blank-padded
999+
type, and a few extra cycles to check the length when storing into
1000+
a length-constrained column. While
1001+
<type>character(<replaceable>n</>)</type> has performance
9991002
advantages in some other database systems, it has no such advantages in
10001003
<productname>PostgreSQL</productname>. In most situations
10011004
<type>text</type> or <type>character varying</type> should be used
@@ -1080,7 +1083,7 @@ SELECT b, char_length(b) FROM test2;
10801083
<row>
10811084
<entry><type>"char"</type></entry>
10821085
<entry>1 byte</entry>
1083-
<entry>single-character internal type</entry>
1086+
<entry>single-byte internal type</entry>
10841087
</row>
10851088
<row>
10861089
<entry><type>name</type></entry>
@@ -1122,7 +1125,7 @@ SELECT b, char_length(b) FROM test2;
11221125
<tbody>
11231126
<row>
11241127
<entry><type>bytea</type></entry>
1125-
<entry>4 bytes plus the actual binary string</entry>
1128+
<entry>1 or4 bytes plus the actual binary string</entry>
11261129
<entry>variable-length binary string</entry>
11271130
</row>
11281131
</tbody>
@@ -2879,13 +2882,13 @@ SELECT person.name, holidays.num_weeks FROM person, holidays
28792882

28802883
<row>
28812884
<entry><type>cidr</type></entry>
2882-
<entry>12 or24 bytes</entry>
2885+
<entry>7 or19 bytes</entry>
28832886
<entry>IPv4 and IPv6 networks</entry>
28842887
</row>
28852888

28862889
<row>
28872890
<entry><type>inet</type></entry>
2888-
<entry>12 or24 bytes</entry>
2891+
<entry>7 or19 bytes</entry>
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<entry>IPv4 and IPv6 hosts and networks</entry>
28902893
</row>
28912894

@@ -3188,6 +3191,12 @@ SELECT * FROM test;
31883191
</programlisting>
31893192
</example>
31903193

3194+
<para>
3195+
A bit string value requires 1 byte for each group of 8 bits, plus
3196+
5 or 8 bytes overhead depending on the length of the string
3197+
(but long values may be compressed or moved out-of-line, as explained
3198+
in <xref linkend="datatype-character"> for character strings).
3199+
</para>
31913200
</sect1>
31923201

31933202
<sect1 id="datatype-xml">

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