I wrote: > BEGIN; > SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; > > DELETE FROM schedule WHERE studentid = ... ; > INSERT INTO schedule (studentid, ...) VALUES (... ); > INSERT INTO schedule (studentid, ...) VALUES (... ); > > COMMIT; > > If you do it like in the above sql code, there is still a problem. The > serializable checking here only works, if DELETE FROM schedule... really > finds at least one row. If it does not, it will not recognize the > serialization problem. So it's still possible that your programm creates > duplicates. > > I have tested this here. I don't really know if this is just the case with > PostgreSQL serializable transactions (MVCC limitation) or a general problem.
There is a detailed description about this problem in Section 12.2.2.1. of the PostgreSQL 8 docs here: http://developer.postgresql.org/docs/postgres/transaction-iso.html (Serializable Isolation versus True Serializability) Best Regards, Michael Paesold ---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings
