isolation-level

问题 Suppose we have a table with an auto-increment primary key. I want to load all IDs greater than the last ID I have seen. SELECT id FROM mytable WHERE id > 10; With the naive approach, I risk skipping IDs: Transaction 1 claims ID 11. Transaction 2 claims ID 12. Transaction 2 commits. I read all IDs >10. I see 12, and next time I will read all IDs >12. I have skipped 11. Transaction 1 commits. For all intents and purposes, ID 11 now exists. As a solution, I propose to do a double check to

问题 Why would a process running a transaction at RC isolation level hold an IX page lock if it is already running a select statement on another table? I mean, i thought that locks are released when the statement finishes (that is why we could have non-repeatable reads). Here's the deadlock xml: <deadlock-list> <deadlock victim="process5cd048"> <process-list> <process id="process5cd048" taskpriority="0" logused="10000" waittime="2220" schedulerid="3" kpid="5764" status="suspended" spid="62" sbid=

问题 When using the Transaction() attribute on a method the default isolation level is ReadCommitted. What I want to do is set the default isolation level to ReadUncommitted in the Spring.NET config ( so as not to modify all the Transaction attribute definitions that exist currently) How do I do it ? Can it be done with Spring.NET 1.2 ? I've tried to follow the documentation using tx:advice etc to no avail. I've even stepped in to the code of Spring with Reflector but all I seem to understand from

问题 After adding a second persistence unit and changing my application's data sources to XADataSource (MySQL), I'm now getting a confusing warning in the glassfish log about isolation levels on my parent entity: WARN o.e.p.s.f.j.ejb_or_metadata : Parent Entity BaseEntity has an isolation level of: PROTECTED which is more protective then the subclass Contact with isolation: null so the subclass has been set to the isolation level PROTECTED. After some research, I think that this isolation level

问题 I want to make my application serialize every transaction by default. I'd then relax isolation based on performance measurements and knowing what data particular actions/transactions use and change. I doubt serializable by default would get into the framework, as it'd slow things down and be difficult to explain. But I don't want to deal with db corruption, and do want internally consistent aggregate calculations. For case-by-case isolation levels there is Rails postgresql how to set

问题 I have a very slow sql transaction, which inserts new rows in the table. All other "select" queries from another connections wait for this transction to unlock the table. Is it posible to fetch old rows from the table, while the first transaction works? SqlExpress 2008 R2. For exapmle: private void button1_Click(object sender, EventArgs e) { System.Threading.Thread t = new System.Threading.Thread( delegate() { var conn = new SqlConnection(@"Data Source=ARTNB\SQLEXPRESS;Initial Catalog=test

问题 This question is a little spin-off from Refactor functions so they can be used within a CTE. The question is simple: is there a different in executing a SELECT query in a READ COMMITTED versus a REPEATABLE READ transaction? We assume that no other queries (even 'SELECT' queries) are done in the transaction. So the transaction is only executing one single SELECT query. 回答1: Normally there won't be a difference for a single SELECT statement. The exception is if the SELECT statement calls user

问题 I'm new to TSQL, still struggling in understanding some basic concepts: My textbook provides an example: there three session(3 query windows, I will refer to them as Connection 1, Connection 2, and Connection 3) Run the following code in Connection 1 to update a row in the Production.Products table, adding 1.00 to the current unit price of 19.00 for product 2. BEGIN TRAN; UPDATE Production.Products SET unitprice += 1.00 WHERE productid = 2; Run the following code in Connection 2 to try to

问题 What is the default isolation level in SQL Server 2005 and in which scenario would you want to change it ? And little explanation about the default isolation level would be appreciated. Thanks in anticipation 回答1: Default = READ COMMITTED You don't need to change it often. Some folk recommend "always use READ UNCOMMITTED" but this is dangerous. As to why , I'd suggest Wikipedia but in summary there are 3 data read issues that can occur: Dirty reads Non-repeatable reads Phantom reads Each of

问题 I am trying to learn how transactions work in DB and to do this I wrote the following test SQL: SAVEPOINT STOP_HERE ON ROLLBACK RETAIN CURSORS; INSERT INTO TESTSCHEMA."test" (ID, NAME) VALUES (89898, 'SDFASDFASD'); ROLLBACK TO SAVEPOINT STOP_HERE; SELECT * FROM TESTSCHEMA."test"; After execution of this code the one row is added into the table. But if I add the following line at the beginning: SET TRANSACTION ISOLATION LEVEL READ COMMITTED; all work as I expected, i.e. transaction correctly