What are the pros/cons from a performance/indexing/data management perspective of creating a one-to-one relationship between tables using the primary key on the child as foreign key, versus a pure surrogate primary key on the child? The first approach seems to reduce redundancy and nicely constrains the one-to-one implicitly, while the second approach seems to be favored by DBAs, even though it creates a second index:

create table parent (
     id integer primary key, 
     data varchar(50)
)

create table child (
     id integer primary key references parent(id), 
     data varchar(50)
)

pure surrogate key:

create table parent (
     id integer primary key, 
     data varchar(50)
)

create table child (
     id integer primary key,
     parent_id integer unique references parent(id), 
     data varchar(50)
)

the platforms of interest here are Postgresql, Microsoft SQL Server.