Folks,
From our docs:
"Adding a column with a non-null default or changing the type of an
existing column will require the entire table and indexes to be
rewritten. As an exception, if the USING clause does not change the
column contents and the old type is either binary coercible to the new
type or an unconstrained domain over the new type, a table rewrite is
not needed ..."
Which is nice, but nowhere do we present users with a set of
binary-compatible data types, even among the built-in types. I'd
happily write this up, if I knew what the binary-compatible data types
*were*.
--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com