[ants_a]

LLMs are not a great source for this type of information. This mess in no way articulated in what way savepoints and transactions are different.

Savepoints are fully equivalent to nested transactions with the constraint that only one is concurrently active. This limitation is just from the SQL standard programming model. At least in PostgreSQL implementation it would be reasonably simple to support multiple concurrent subtransactions. They are even called subtransactions internally.