PostgreSQL primary key length limit

Question

What is the limit of the length of primary key column? I'm going to use varchar as primary key. I've found no info, how long it can be, since PostgreSQL does not require to specify varchar limit when used as primary key?

Answer 1

The maximum length for a value in a B-tree index, which includes primary keys, is one third of the size of a buffer page, by default floor(8192/3) = 2730 bytes.