Comparing two slices within one table efficiently

I have a table with the following simplified form:

create table t (
run_id integer,
domain_id integer,
mta_id integer,
attribute1 integer,
attribute2 integer,
unique(run_id, domain_id, mta_id)
);

The table has about 1 million rows with run_id=1, another 1 million rows with run_id=2, and so on.

I need to efficiently query the differences between "runs" - i.e. For each (domain_id, mta_id) tuple in run 1, is there a coresponding tuple in run 2 where either attribute1 or attribute2 have changed?

The only way I have been able to think of doing this so far is an o(n^2) search, which even with indexes takes a long time. e.g.

select * from t t1 where exists (select 1 from t t2 where t2.mta_id=t1.mta_id and t2.domain_id=t1.domain_id and (t2.attribute1 != t1.attribute1 or t2.attribute2 != t1.attribute2)

This query takes millenia...

Any help would be greatly appreciated. I hope I am naively missing some obvious alternative strategy, since this sort of operation must be common in databases.

Thanks,
Ken

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