Depending on the system you use snapshot isolation sometimes allows you to get an snapshot id which allows you to use the same snapshot in other (read only) tra

Depending on the system you use snapshot isolation sometimes allows you to get an snapshot id which allows you to use the same snapshot in other (read only) transactions. Furthermore even read only transactions can fail during the transaction, especially longer running ones. Sometimes that is fine, and even required. But many other times reading a snapshot even if it becomes stall is preferable. Through I wouldn't say snapshot is it's own isolation level. It's more like a specific way you can run read only serializable transactions by telling the DB "pretend in this transaction(only) any changes by other transactions happen after I ended the transaction".