On an RDMS which I used in the 1990s and 2000s, b-tree indices of sequences
would get unbalanced, since every new leaf was added to the far right
corner of the tree.
Sure, they would auto-balance *to a degree* during node splits, but all
those "far-right corner" inserts still left them pretty lopsided.
Thus, they provided a utility which we could use to determine the
lopsidedness, and thus decide when to rebuild an index.
Does Postgresql keep b-tree indexes on sequences fully balanced? If not,
how do I see how unbalanced they are? (Assume PG12+.)