Very slow INFORMATION_SCHEMA

Hi,

I'm porting an application written with pretty portable SQL, but tested
almost exclusively on MySQL.

I'm wondering why would this query take about 90 seconds to return 74 rows?

SELECT INFORMATION_SCHEMA.TABLE_CONSTRAINTS.CONSTRAINT_NAME,
INFORMATION_SCHEMA.TABLE_CONSTRAINTS.TABLE_NAME,
INFORMATION_SCHEMA.TABLE_CONSTRAINTS.TABLE_NAME,
INFORMATION_SCHEMA.TABLE_CONSTRAINTS.CONSTRAINT_TYPE,
INFORMATION_SCHEMA.KEY_COLUMN_USAGE.COLUMN_NAME,
INFORMATION_SCHEMA.KEY_COLUMN_USAGE.REFERENCED_TABLE_NAME,
INFORMATION_SCHEMA.KEY_COLUMN_USAGE.REFERENCED_COLUMN_NAME
FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS,
INFORMATION_SCHEMA.KEY_COLUMN_USAGE
WHERE
INFORMATION_SCHEMA.TABLE_CONSTRAINTS.CONSTRAINT_NAME=INFORMATION_SCHEMA.KEY_COLUMN_USAGE.CONSTRAINT_NAME
AND
INFORMATION_SCHEMA.TABLE_CONSTRAINTS.CONSTRAINT_SCHEMA=INFORMATION_SCHEMA.KEY_COLUMN_USAGE.CONSTRAINT_SCHEMA
AND
INFORMATION_SCHEMA.TABLE_CONSTRAINTS.CONSTRAINT_SCHEMA='mydbname'
AND
INFORMATION_SCHEMA.TABLE_CONSTRAINTS.CONSTRAINT_TYPE='FOREIGN KEY'
ORDER BY INFORMATION_SCHEMA.TABLE_CONSTRAINTS.TABLE_NAME,
INFORMATION_SCHEMA.KEY_COLUMN_USAGE.ORDINAL_POSITION

An equivalent query with the same data set on the same server takes a
couple of milliseconds on MySQL 5.
Is it something I'm doing wrong or it's just that PostgreSQL
INFORMATION_SCHEMA is not optimized for speed? BTW, what I'm trying to
do is get some info on every FOREIGN KEY in a database.

It's PostgreSQL 8.2.7 on Fedora 8 64, Athlon 64 X2 3600+.

Ernesto