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Remove obsolete claim that char(n) is more efficient than other text types.

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Tom Lane 2000-11-30 18:46:42 +00:00
parent 1f5cc8c78a
commit b73ecebf05
2 changed files with 15 additions and 19 deletions
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14
doc/FAQ
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@ -811,19 +811,17 @@ Type Internal Name Notes
"char" char 1 character
CHAR(#) bpchar blank padded to the specified fixed length
VARCHAR(#) varchar size specifies maximum length, no padding
TEXT text length limited only by maximum row length
BYTEA bytea variable-length array of bytes
TEXT text no specific upper limit on length
BYTEA bytea variable-length byte array (null-safe)
You will see the internal name when examining system catalogs and in
some error messages.
The last four types above are "varlena" types (i.e., the first four
bytes are the length, followed by the data). char(#) allocates the
maximum number of bytes no matter how much data is stored in the
field. text, varchar(#), and bytea all have variable length on the
disk, and because of this, there is a small performance penalty for
using them. Specifically, the penalty is for access to all columns
after the first column of this type.
bytes on disk are the length, followed by the data). Thus the actual
space used is slightly greater than the declared size. However, these
data types are also subject to compression or being stored out-of-line
by TOAST, so the space on disk might also be less than expected.
4.16.1) How do I create a serial/auto-incrementing field?

20
doc/src/FAQ/FAQ.html
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@ -534,7 +534,7 @@ A report generator? An embedded query language interface?</H4><P>
We have a nice graphical user interface called <I>pgaccess,</I> which is
shipped as part of the distribution. <I>Pgaccess</I> also has a report
generator. The Web page is <A HREF=
generator. The Web page is <A HREF=""
"http://www.flex.ro/pgaccess">http://www.flex.ro/pgaccess</A><P>
We also include <I>ecpg,</I> which is an embedded SQL query language interface for
@ -996,20 +996,18 @@ Type Internal Name Notes
"char" char 1 character
CHAR(#) bpchar blank padded to the specified fixed length
VARCHAR(#) varchar size specifies maximum length, no padding
TEXT text length limited only by maximum row length
BYTEA bytea variable-length array of bytes
TEXT text no specific upper limit on length
BYTEA bytea variable-length byte array (null-safe)
</PRE><P>
You will see the internal name when examining system catalogs
and in some error messages.<P>
The last four types above are "varlena" types (i.e., the first four bytes
are the length, followed by the data). <I>char(#)</I> allocates the
maximum number of bytes no matter how much data is stored in the field.
<I>text, varchar(#),</I> and <I>bytea</I> all have variable length on the disk,
and because of this, there is a small performance penalty for using
them. Specifically, the penalty is for access to all columns after the
first column of this type.<P>
The last four types above are "varlena" types (i.e., the first four
bytes on disk are the length, followed by the data). Thus the actual
space used is slightly greater than the declared size. However, these
data types are also subject to compression or being stored out-of-line
by TOAST, so the space on disk might also be less than expected.<P>
<H4><A NAME="4.16.1">4.16.1</A>) How do I create a