Performance using char keys ?

Has anybody experienced the performance behaviour when using character  datatype instead of integer datatype for key attributes.  

 I ask myself if building and accessing indexes on character columns is  much slower than on integer. (I'm sure it is slower, but how much slower
 ?)  

 In the moment, mostly all of the tables in our project do have a object  identifier which is integer. This obj_id is heavily accessed in all  kinds of operations on our data modell (especially as a join attribute,  when accessing objects which are represented by attributes of different  tables).
 For different reason there are now requests that we should change the  datatype to character.  

 It would be great if some guys out there could share their experience  with me !!!  

 bye pit :-)  

Peter R. Messerer        Tel.:   08102 / 748140
Ahornring 33             Fax :   08102 / 748139
85635 Siegertsbrunn      email:  Peter.Messerer_at_munich.netsurf.de
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