1, the four major characteristics of database transactions --ACID properties
Atomic: A transaction is the smallest indivisible unit of work, the operation of the entire transaction either all succeed or all fail rollback.
Consistency: read the outcome of the transaction on the same data is the same.
Isolation: a firm to make changes before final submission, to other transactions is not visible
Durability: Once a transaction is committed, to modify its made permanently stored in the database
2, isolation level
Uncommitted read: modified transaction not submitted in time, is also visible to other transactions
Read Committed: Firm changes made before committing to other transactions is not visible (to prevent dirty reads)
Repeatable Read: ensure the same transaction reads the same data multiple times results are the same (to prevent dirty reads, non-repeatable read)
Serializable: serial execution force, interference between the transaction (to prevent dirty reads, non-repeatable read, phantom read
