Richard Maher wrote:
Arne Vajh?j wrote ...
Almost all database have it at the SQL level:
http://dev.mysql.com/doc/refman/5.5/en/set-transaction.html
http://www.postgresql.org/docs/9.1/static/sql-set-transaction.html and
http://www.postgresql.org/docs/9.1/static/transaction-iso.html
http://msdn.microsoft.com/en-us/library/ms173763.aspx
http://docs.oracle.com/cd/B10500_01/server.920/a96524/c21cnsis.htm
Is anyone else of the opinion that Oracle really does not support the
serializable isolation level? (At least not in the way that SQL Server, Rdb,
Are you referring to their database product or some other product, such as Java?
and I'm sure others do) That is, it doesn't prevent inserts to the other
txn's result-set,touched-rows by locking but rather fudges some sort of
snapshot/consistent-view of old data. (And even then with restrictions)
Eg: - select count(*) from employees where dept_code=1;
They do support SERIALIZABLE isolation, and properly by all evidence:
<http://docs.oracle.com/cd/E11882_01/server.112/e26088/statements_10005.htm#SQLRF01705>
"ISOLATION LEVEL Clause
"Use the ISOLATION LEVEL clause to specify how transactions containing database
modifications are handled.
"The SERIALIZABLE setting specifies serializable transaction isolation mode as defined in the
SQL standard. If a serializable transaction contains data manipulation language (DML) that
attempts to update any resource that may have been updated in a transaction uncommitted at
the start of the serializable transaction, then the DML statement fails."
See also
<http://docs.oracle.com/cd/E11882_01/server.112/e25789/consist.htm#BABEAFAH>
There's nothing in the definition of SERIALIZABLE transactions that requires locking.
<http://en.wikipedia.org/wiki/Isolation_(database_systems)#Serializable>
So whatever anyone else's opinion, or yours, the facts seem to be that Oracle Database properly supports SERIALIZABLE transaction isolation. Why do you ask for opinion when facts are in evidence?