isolation-level

Do you know the default isolation level of the transactions used in Django? Is it possible to set the isolation level in the database independent way? I'm mainly interested in mysql and postgres. Peter Lundberg You can also change this per client / session using the django database options, like this: DATABASE_OPTIONS = { "init_command": "SET storage_engine=INNODB, SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED", } The isolation level isn't changed by mysql drivers so it depends on the server's default isolation level. Sebastian Noack At the moment django does not set the isolation level.

I tried this with MySQL Server 5.5: 1) ensured that transaction isolation level is repeatable_read 2) started shell-1, started a transaction in it, then read a value through select 3) started shell-2, started a transaction in it, then read the same value through select 4) in shell-1, updated the value to value + 1 and committed 5) in shell-2, updated the value to value + 1 and committed The value lost one of its updates and was incremented only by 1. Now, as I understand it, RR uses shared read locks and exclusive write locks, which means that in #4 and #5 above, the transactions should have

What is the difference between non-repeatable read and phantom read? I have read the Isolation (database systems) article from Wikipedia , but I have a few doubts. In the below example, what will happen: the non-repeatable read and phantom read ? Transaction A SELECT ID, USERNAME, accountno, amount FROM USERS WHERE ID=1 OUTPUT: 1----MIKE------29019892---------5000 Transaction B UPDATE USERS SET amount=amount+5000 where ID=1 AND accountno=29019892; COMMIT; Transaction A SELECT ID, USERNAME, accountno, amount FROM USERS WHERE ID=1 Another doubt is, in the above example, which isolation level

Could some one please help me understand when to use SNAPSHOT isolation level over READ COMMITTED SNAPSHOT in SQL Server? I understand that in most cases READ COMMITTED SNAPSHOT works, but not sure when go for SNAPSHOT isolation. Thanks READ COMMITTED SNAPSHOT does optimistic reads and pessimistic writes. In contrast, SNAPSHOT does optimistic reads and optimistic writes. Microsoft recommends READ COMMITTED SNAPSHOT for most apps that need row versioning. Read this excellent Microsoft article: Choosing Row Versioning-based Isolation Levels . It explains the benefits and costs of both isolation

The following method is supposed to peroform a dirty read on an open connection. There are no transactions. Where do I set IsolationLevel? public string DoDirtyRead(string storedProcName, SqlConnection connection) { using (SqlCommand command = new SqlCommand(storedProcName, connection)) { command.CommandType = CommandType.StoredProcedure; // HOW TO SET IsolationLevel to READ_UNCOMMITTED here? command.ExecuteNonQuery(); } } On the BeginTransaction method: ( MSDN link ) And if you just want to use hints in your SP at the table level, use WITH(NOLOCK) - but use at your own risk. If you don't want

Using "repeatable read" it should be possible to produce a phantom read, but how? I need it for an example teaching CS-students. I think that I must make a "SELECT ... WHERE x<=888" on a non-indexed field x, with an upperlimit 888 not present, and then on another connection insert a new row with a value just below 888. Except it doesn't work. Do I need a very large table? Or something else? dani herrera Erik, I come just from test it with a very large number of rows. You will never found phantoms on InnoDB mysql with read commited or more restricted isolation level. It is explained on