Induction #
1, the transaction: ACID is Atomic (atomic) Consistency (Consistency) Isolation (isolation) Durability Rev (persistent)
database transaction data is indivisible series of operations. Above "a series of operations" refers to a "SQL statements submitted." Operations in a transaction either do or do not do, if an accident occurs while doing it before the transaction is rolled back to the start, finish the transaction can not go back, do not cross modify data between concurrent transactions. These requirements are guaranteed by the database management system of recovery and concurrency control mechanism.
2, concurrency control:
Causes concurrent access to data that occur when multiple transactions access the same data object intersecting which a transaction data modification operation, hinder access to the accuracy of the results of other transactions. Lock controlled by the data object you want to access transactions. If the transaction is subject to only read data request shared locks S, does not interfere with other transactions read; if the transaction is to modify the data object is added to an exclusive lock request X, reject any other transaction operations.
#to sum up
# Overview