add constraint freeze table

I have a 10M records table. I notice that if I try to add a constraint, like pk or not null, the entire table freeze for two hours until the constraint is created. I cannot even do simple select. Why it that?

What I did is I drop a primary key and recreate it - alter table table_name add constraint pk_table_name primary key (id) using index tablespace data1;

ewong Received on Wed Jul 25 2001 - 20:53:27 CDT