transaction-isolation

问题 We have a table in MySQL using InnoDB, and we are using a transaction isolation level of read uncommitted. Why does setting @x as shown acquire a lock? mysql> set @x = (select userID from users limit 1); Query OK, 0 rows affected (0.02 sec) mysql> Trying to update this table from another prompt results in a timeout error: mysql> update users set userID = 1; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction 回答1: For what it's worth, this locking is not limited to READ

问题 We have a table in MySQL using InnoDB, and we are using a transaction isolation level of read uncommitted. Why does setting @x as shown acquire a lock? mysql> set @x = (select userID from users limit 1); Query OK, 0 rows affected (0.02 sec) mysql> Trying to update this table from another prompt results in a timeout error: mysql> update users set userID = 1; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction 回答1: For what it's worth, this locking is not limited to READ

来源： https://stackoverflow.com/questions/60854328/mysql-exclusive-lock

问题 I want to try transaction isolation using PostgreSQL with pgadmin. First I inserted a new record inside BEGIN but without COMMIT. BEGIN; INSERT INTO my_table(id,value) VALUES (1,'something'); //UNCOMMITTED Then, I tried to read the uncommitted data BEGIN TRANSACTION ISOLATION LEVEL READ UNCOMMITTED; SELECT * FROM my_table COMMIT; But I couldn't find the new record. What's wrong? 回答1: PostgreSQL does not support dirty reads ( READ UNCOMMITTED ). As @a_horse_with_no_name pointed out, the manual

问题 I have an application that uses hibernate version 3.6.4, and c3p0 version 0.9.1.2 for connection pooling. My underlying RDBMS is MySql version 5.0.67. My installation of MySql indicates that the default transaction isolation level is "REPEATABLE-READ" (4): mysql> select @@GLOBAL.tx_isolation, @@tx_isolation; +-----------------------+-----------------+ | @@GLOBAL.tx_isolation | @@tx_isolation | +-----------------------+-----------------+ | REPEATABLE-READ | REPEATABLE-READ | +-----------------

问题 I have a bunch of utility procedures that just check for some conditions in the database and return a flag result. These procedures are run with READ UNCOMMITTED isolation level, equivalent to WITH NOLOCK. I also have more complex procedures that are run with SERIALIZABLE isolation level. They also happen to have these same kind of checks in them. So I decided to call these check procedures from within those complex procedures instead of replicating the check code. Basically it looks like

问题 Lets say we have a usual situation with Order_Header and Order_LineItems tables. Also, lets say we have transactions for creating, updating and selecting Orders. Like: Create: BEGIN TRANSACTION INSERT INTO Order_Headers... SET @Id = SCOPE_IDENTITY() INSERT INTO Order_LineItems...(using @Id) DECLARE @SomeVar INT --just example to show update dependant on select SELECT @SomeVar = COUNT(*) Order_Headers WHERE OrderDate > '1-1-2017' UPDATE Order_Headers SET SomeValue = @SomeVar WHERE Id = @Id

问题 I am using Spring transaction management to control a application with hibernate, it uses two instance of threads to access concurrency database and modify one table. It is ensuring that the values are conserved. The table before is: quantidade_livro_id | quantidade | livro_id | tt ---------------------+------------+----------+---- 7 | 100 | 3 | as 5 | 100 | 1 | as 6 | 100 | 2 | as And the table after: quantidade_livro_id | quantidade | livro_id | tt ---------------------+------------+-------

问题 I have a requirement to start new Transaction within an ongoing Transaction so that an exception in 2nd transaction will rollback only new transaction not the old one. This I am doing by setting propagation attribute in 2nd transaction like this: @Transactional(propagation = Propagation.REQUIRES_NEW) This created a new Transaction, but the new Transaction needs to read some uncommitted data of the first transaction (dirty read), and also update that data. This I am trying to do by setting

问题 If I SELECT... FOR UPDATE a row in a transaction, it will obviously block the row from being written to, but will it disallow reads as well? I'd prefer to still be able to read from the row, so if the answer is yes, can you provide a solution to work this? 回答1: You can read just fine. There are lock modes that prevent reading but this isn't one of them. http://www.postgresql.org/docs/current/static/explicit-locking.html 来源： https://stackoverflow.com/questions/12029470/can-a-locked-row-in