[kbaldor]

Databases aren't my field, but I would expect this to hurt performance by decreasing locality of keys.

This, of course, assumes that temporally-adjacent additions are related, but this seems like a common case for large data sets since they often arise from a series of measurements or transactions.

I created this account to make this reply because I imagine that someone here is expert enough to set me straight if I'm mistaken.

[wulczer]

Postgres at least will store rows roughly in insert order. So whether you're using integers or UUIDs for primary keys won't affect on-disk layout.

When scanning the index, the database will be traversing it in btree order, anyway, so as long as the values are comparable, ints or UUIDs shouldn't matter much.

[crdoconnor]

It might negatively affect performance, yes.

Performance shouldn't affect the decision to make it default, however. That would be premature optimization.

The only good reason I can think of for not making it default would be backwards compatibility.