I ran some timing tests to check the performance of varchar() vs char16.
The results of the test indicate that there is no difference in
performance (within the timing scatter of the tests):

char16	vc(16)
 0.99s	 1.05s	1 row (this measures startup time, not types)
39.29s	39.28s	~65000 rows

The char2,4,8,16 types seem to have no value-added over the
better-supported char(), varchar(), text types; I am considering
removing them from the backend, and instead have the parser
transparently translate the types into varchar() (or char() - I'm not
certain which is a better match for the types) for v6.4. Applications
would not have to be changed.

Comments?

>From the logic char(16) would be the correct replacement.
I also support the idea to remove char-char16. The problems I see are:
	1. char2-16 does not have the 4 byte var header (this would be good for the char() type too)
	2. per definition 'a    ' = 'a'  for the char type but 'a    ' <> 'a' for varchar

Note the correct behavior of postgresql:
test=> select 'a   '::char(4) = 'a'::char(4);
?column?
--------
t
(1 row)

test=> select 'a   '::varchar(4) = 'a'::varchar(4);
?column?
--------
f
(1 row)

but note the "incorrect" (char-char16 beeing a fixed length type) behavior of the char-char16 code 
test=> select 'a   '::char4 = 'a'::char4;
?column?
--------
f
(1 row)

so the current char2-16 code behaves more like varchar. I don't know if anybody does
rely on this behavior. If not, I would vote to change the char-char16 with the char()
type and remove the varhdr from char(). I like getting a simple char * into my C function.
(see point 1)

Andreas





Wed, 11 Mar 1998 16:30:17 +-100
Zeugswetter Andreas <andreas.zeugswetter@telecom.at>
AW: [HACKERS] varchar() vs char16 performance
> so the current char2-16 code behaves more like varchar. I don't know if anybody does
> rely on this behavior. If not, I would vote to change the char-char16 with the char()
> type and remove the varhdr from char(). I like getting a simple char * into my C function.
> (see point 1)

Removing the header from char() types is possible now that we have
atttypmod, but I doubt atttypmod is available in all places that the
length of the type is needed.  varlena is supported all over the place
in the backend.

-- 
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Wed, 11 Mar 1998 13:50:13 -0500 (EST)
Bruce Momjian <maillist@candle.pha.pa.us>
Re: AW: [HACKERS] varchar() vs char16 performance