index as large as table

Hi,

While testing 8.1dev I came to this:

CREATE TABLE t (
a int,
b int
PRIMARY KEY (a,b));

In  that case, the index is as big as the table.

My question is is it worthwhile to have such index peformance wise.
I understand I'd loose uniqness buthas such an index any chance to be used
against seq scan.

Is there any chance we have a "btree table" in the future for that case?

Regards,

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