Sequences in Postgres are updated even if a transaction is rolled back. It's pretty easy to see why that's important, especially when dealing with concurrent tr

Sequences in Postgres are updated even if a transaction is rolled back. It's pretty easy to see why that's important, especially when dealing with concurrent transactions. You can't give out the same number to multiple transactions without causing a bunch of unique constraint violations. And you can't retroactively decrease a sequence number without affecting all the other transactions currently executing. You could in theory go back and plug in the gaps in a sequence, but it's more important to guarantee that a single thread of execution will always see increasing numbers than it is to guarantee that all numbers will eventually be handed out to a successful transaction.