Foreign key / performance question

Hi !,

 

Is it wise to define foreign keys for referential entegrity ?

Example : I have a customer table with 40 fields.  Out of that 40 fields, 10 fields contain information linked to other tables.   So, is defining foreign keys for these 10 fields a good idea ?  Because from what I understand, for every foreign key, there is an index defined.  So, all these indexes has to be maintained.  Is that killing performance ?  What's the best practise : defining foreign keys or not ?

 

Thanks a lot,

Nico Callewaert