PostgreSQL primary key length limit

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 pr开发者_C百科imary key?

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.

I believe that maximum varchar length is a Postgres configuration setting. However, it looks as though it can't exceed 1GB in size.

http://wiki.postgresql.org/wiki/FAQ#What_is_the_maximum_size_for_a_row.2C_a_table.2C_and_a_database.3F

That having been said, it's probably not a good idea to have a large varchar column as a primary key. Consider using a serial or bigserial (http://www.postgresql.org/docs/current/interactive/datatype-numeric.html#DATATYPE-SERIAL)

You should made a test.

I've made tests, with table, that have single varchar column as primary key, on PostgreSQL 8.4. The result is, that I was able to store 235000 ASCII characters, 116000 polish diactrical characters (f.g. 'ć') or 75000 chinese (f.g. '汉'). For larger sets I've got a message:
BŁĄD: index row size 5404 exceeds btree maximum, 2712
However, the message told that:
Values larger than 1/3 of a buffer page cannot be indexed.
So the values were allowed, however not the whole string was used for uniqueness check.

Well, this is a very large amount of data that you can put in that column. However, as noted above, your design is poor if you will have to use such long values as keys. You should use artificial primary key.