Just to clarify, these are not serializable transactions, they're snapshot isolation. The serialization this document talks about refers to BEGIN CONCURRENT all

Just to clarify, these are not serializable transactions, they're snapshot isolation. The serialization this document talks about refers to BEGIN CONCURRENT allowing multiple writing transactions to co-exist, but COMMITs do not happen in parallel; at any given point in time only one COMMIT can be in-progress. Hence, serialized.