The user docs say about column defaults: "
The value is any variable-free expression (subqueries and cross-references to other columns in the current table are not allowed)"
And also say about pg_get_expr "If the expression might contain Vars, specify the OID of the relation they refer to as the second parameter; if no Vars are expected, zero is sufficient"
Since defaults can't contain Vars, this patch converts the second parameter to zero in places where pg_get_expr is invoked on column defaults. Doing this drops the time needed to run `pg_dump -s` on a 1600 column table with defaults on all columns by a factor of 40. So pg_upgrade users with such tables should see a big win (cc Justin).
I also made the change to the other places in the source which I could identify with this issue. \d is now much faster for such tables as well, but I didn't test the performance of the others.
There are surely more opportunities to speed up pg_get_expr for things other than column defaults, but I wanted to submit this for now.
I have not tested the pg_upgrade using source versions <8.4, because I can't get anything that old to "make check" correctly, so I have nothing to test on.
Cheers,
Jeff