isolation-level | 易学教程

How programmatically enable READ COMMITTED SNAPSHOT in SQL Server?

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问题 I need to programmatically enable READ COMMITTED SNAPSHOT in SQL Server. How can I do that? 回答1: I recommend switching to single-user mode first. That ensures you're the only connection. Otherwise, the query might be suspended. From: http://msdn.microsoft.com/en-us/library/ms175095.aspx When setting the READ_COMMITTED_SNAPSHOT option, only the connection executing the ALTER DATABASE command is allowed in the database. There must be no other open connection in the database until ALTER DATABASE

InnoDB SELECT … FOR UPDATE statement locking all rows in a table

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问题 MySQL Server version 5.1.41 with InnoDB plugin enabled. I have the following three tables for invoices: invoices, invoice_components and invoice_expenses. Table invoices has invoice_id primary key. Both invoice_components and invoice_expenses are linked to table invoices with invoice_id as a non-unique foreign_key (each invoice can have more than one component and more than one expense). Both tables have a BTREE index for this foreign key. I have the following transactions: transaction 1

Isolation levels in oracle [closed]

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Closed . This question needs to be more focused. It is not currently accepting answers. Learn more . Want to improve this question? Update the question so it focuses on one problem only by editing this post . Closed 8 months ago . I would like to know different isolation levels with respect to commit, and would also like to know about row-level and table-level lock. ANSI/ISO SQL defines four isolation levels: serializable repeatable read read committed read uncommitted According to Oracle's Database Development Guide, chapter 6.6.1: Transaction Interaction and Isolation Level , you can request

Get current .net TransactionScope IsolationLevel

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问题 I have an utility method creating TransactionScope in my application. I want to do a unit test to validate that the returned TransactionScope has the correct IsolationLevel set, to be sure that nobody can modify the code without breaking the tests. System.Transactions.Transaction scope does not have public properties exposing information like that. (http://msdn.microsoft.com/en-us/library/system.transactions.transactionscope.aspx) Any way to get this information? 回答1: Can you run a SQL query

Workarounds for ReadUncommitted Isolation level in an SSIS package

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The ReadUncommitted IsolationLevel in SSIS is a bug acknowledged by Microsoft for the following but 'Wont fix' as described below. http://connect.microsoft.com/SQLServer/feedback/details/498891/ssis-setting-isolationlevel-to-readuncommitted-still-uses-read-committed#details What would be the workaround(s) for the same? yes, but you have to inform the sql command on your source instead of selecting a table and set the isolation level before the execution: SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED select * from test_isolation and the package should have the serializable isolation level

set isolation level for postgresql stored procedures

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问题 Hopefully a simple question, but one for which I haven't readily found a decent answer. I'm reliably informed that stored procedures (user-defined DB functions) in PostgreSQL (specifically, version 9.0.4) are inherently transactional, inasmuch as they are called through a SELECT statement which itself is a transaction. So how does one choose the isolation level of the stored procedure? I believe in other DBMSs the desired transactional block would be wrapped in a START TRANSACTION block for

Some clarifications on different Isolation level in database transaction?

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Below is the statement written from Wikipedia's Isolation article about REPEATABLE READS In this isolation level, a lock-based concurrency control DBMS implementation keeps read and write locks (acquired on selected data) until the end of the transaction. However, range-locks are not managed, so the phantom reads phenomenon can occur (see below). My question here is when does the the transaction begin and end respectively. If we take the example of Non-repeatable reads with REPEATABLE READS Isolation level at the same link , as per my understanding trnsaction 1 begin when first query is fired

What is (are) difference between NOLOCK and UNCOMMITTED

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问题 I use SQL Server 2012. I write two queries but what is a different between NOLOCK and UnCommitted ? SELECT lastname, firstname FROM HR.Employees with (READUNCOMMITTED) SELECT lastname, firstname FROM HR.Employees with (NoLock) 回答1: NOLOCK : Is equivalent to READUNCOMMITTED (source : MSDN ) NOLOCK or READUNCOMMITTED Specifies that dirty reads are allowed. No shared locks are issued to prevent other transactions from modifying data read by the current transaction, and exclusive locks set by

How are locking mechanisms (Pessimistic/Optimistic) related to database transaction isolation levels?

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问题 I am writing a web application where two different users can update a list of things, to do list, for example. I have come to realize that, optimistic locking mechanism works best since I don't expect high contention. I was looking at transaction isolation levels and now I am a little confused. Looks like different transaction isolation levels also solve similar problems. How are these two different concepts related to each other? If possible, with a simple example. 回答1: Both of these things

What is (are) difference between NOLOCK and UNCOMMITTED

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I use SQL Server 2012. I write two queries but what is a different between NOLOCK and UnCommitted ? SELECT lastname, firstname FROM HR.Employees with (READUNCOMMITTED) SELECT lastname, firstname FROM HR.Employees with (NoLock) NOLOCK : Is equivalent to READUNCOMMITTED (source : MSDN ) NOLOCK or READUNCOMMITTED Specifies that dirty reads are allowed. No shared locks are issued to prevent other transactions from modifying data read by the current transaction, and exclusive locks set by other transactions do not block the current transaction from reading the locked data. Allowing dirty reads can