Is it possible to implement nested transactions in a system, and in what cases is it permissible?

In the standard Go library (package database/sql), nested transactions are not directly supported, as most DBMSs do not implement full nested transactions. Instead, savepoints are often used, which allow rolling back to a specific point within a transaction.

Possible options:

• Use savepoints if supported by the DBMS (e.g., PostgreSQL, MySQL). In Go, this can be done by executing SQL commands SAVEPOINT, ROLLBACK TO SAVEPOINT.
• Emulate nested transactions through separate transactions, but this is not always correct from a business logic perspective.

When is it permissible:

• When you need to partially roll back changes within a large transaction without a full rollback.
• In complex operations with multiple stages, where each stage can be rolled back separately.

Example of using savepoints in Go:

trx, err := db.Begin()
if err != nil {
    // handle error
}
_, err = trx.Exec("SAVEPOINT sp1")
if err != nil {
    trx.Rollback()
    return err
}
// Perform operations
// On error:
_, err = trx.Exec("ROLLBACK TO SAVEPOINT sp1")
// Continue or commit fully
err = trx.Commit()

Thus, nested transactions are implemented via savepoints, not through nested Begin/Commit calls.