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Add mention of TOAST storage for character columns.

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This commit is contained in:
Bruce Momjian 2002-07-16 04:45:59 +00:00
parent b3341ddbf2
commit d76eef3e7c
1 changed files with 15 additions and 14 deletions
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29
doc/src/sgml/datatype.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.94 2002/07/16 03:30:26 momjian Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.95 2002/07/16 04:45:59 momjian Exp $
-->
<chapter id="datatype">
@ -843,19 +843,20 @@ CREATE TABLE <replaceable class="parameter">tablename</replaceable> (<replaceabl
</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 will be compressed by the system
automatically, so the physical requirement on disk may be less.
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 change
this because with multibyte character encodings the number of
characters and bytes can be quite different anyway. If you desire
to store long strings with no specific upper limit, use <type>text</type>
or <type>character varying</type> without a length specifier,
rather than making up an arbitrary length limit.)
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 may be less. Long values are also
stored in background tables so they don't interfere with rapid
access to the 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
change this because with multibyte character encodings the number of
characters and bytes can be quite different anyway. If you desire to
store long strings with no specific upper limit, use
<type>text</type> or <type>character varying</type> without a length
specifier, rather than making up an arbitrary length limit.)
</para>
<tip>