Thread: Maximum size of the primary key

Hi!

I'm an absolute beginner to PostgreSQL and
there's probably stupid questions coming up
more than just this one:

Is there a limit to the bytesize of the
primary key? (I'm migrating from MySQL
and there it was only 255). I couldn't find
this in the documentation at first glance.

Jass

jaanush@hot.ee (Jass) writes:
> Is there a limit to the bytesize of the
> primary key? (I'm migrating from MySQL
> and there it was only 255).

btree index entries (primary key or not) are limited to 1/3 page, or
about 2700 bytes in a standard installation.  In the case of
compressible types like text or varchar, compression can be applied
first, so you'd probably find you could get away with field widths
up to 4k or so.  If you have entries wider than that, I'd begin to
question whether an index on the field really makes sense ...

            regards, tom lane