IS it a good practice to use SERIAL as Primary Key?

["carter ck" <carterck32(at)hotmail(dot)com>]

Hi all,

I am wonderring if it is a good practice to use SERIAL index as primary key, 
as it is only available up to 9999999?

Currently i am dealing with storing LDAP users into Postgres and i am 
looking for a better way to make use of the DN as primary key instead of 
SERIAL index.

Any advice or suggestion is appreciated.

Thanks.

Regards,
Carter

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