It is in the Wiki: https://wiki.postgresql.org/wiki/Serializable https://wiki.postgresql.org/wiki/Serializable Any transaction which is run at a transaction iso

It is in the Wiki: https://wiki.postgresql.org/wiki/Serializable https://wiki.postgresql.org/wiki/Serializable Any transaction which is run at a transaction isolation level other than SERIALIZABLE will not be affected by SSI. If you want to enforce business rules through SSI, all transactions should be run at the SERIALIZABLE transaction isolation level, and that should probably be set as the default. I guess it is the same for all MVCC databases. They don't want to acquire a read lock just in case another transaction is in Serializable