Thread

1. AW: [HACKERS] varchar() vs char16 performance

   Andreas Zeugswetter <andreas.zeugswetter@telecom.at> — 1998-03-11T15:30:17Z

   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
   
   
   
   
   
   

2. Re: AW: [HACKERS] varchar() vs char16 performance

   Bruce Momjian <maillist@candle.pha.pa.us> — 1998-03-11T18:50:13Z

   > 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.
   
   -- 
   Bruce Momjian                          |  830 Blythe Avenue
   maillist@candle.pha.pa.us              |  Drexel Hill, Pennsylvania 19026
     +  If your life is a hard drive,     |  (610) 353-9879(w)
     +  Christ can be your backup.        |  (610) 853-3000(h)