Four transaction isolation level

Database isolation level operations

• Setting the isolation level: SET TX_ISOLATION = 'the READ-UNCOMMITTED'
• View isolation levels: the SELECT @@ TX_ISOLATION

A, Read Uncommitted - read uncommitted content

• A transaction can view uncommitted content
• Problems often produce dirty read (dirty read: to read the contents of other uncommitted transactions (executed))
  opened on the same data tables A, B two transaction (A, B cross transaction) Start Transaction
  A transaction only query the contents of the data table , B additions and deletions to make the transaction, but not the operation commit (submitted)
  a query to the transaction can still change the data in the table (the query to the content uncommitted - dirty reads)

Two, Read Committed - read submissions

• A transaction can only see content you have submitted
• Problems often produce non-repeatable read (non-repeatable reads: select statement to perform the same transaction in the same different results)
  for opening the same data table A, B two transaction (A, B cross transaction) Start Transaction
  A transaction data inquiry only contents of the table, B additions and deletions to make the transaction, but not the operation commit (submitted)
  a transaction is less than the data change query table
  B transaction commit
  data change (a a query found in two, different results - no repeatable read)

Three, Repeatable Read - can be re-read

• The results obtained when the same data is read multiple concurrent instances of the same transaction
• MySQL's default transaction isolation level
• Problems often produce phantom read (phantom reads: multiple different results (phantom line) reading)
  open on the same data tables A, B two transaction (A, B cross transaction) Start Transaction
  A transaction only query the contents of the data table , B additions and deletions to make the transaction, but not the operation commit (submitted)
  a transaction is less than the data change query table
  B transaction commit
  a query data transaction can not change the contents of table
  a, as
  a may query the data in table change

Four, Serializable - serialization

• Highest level of isolation
• Plus a shared lock to the transaction, while only one transaction operations, to solve the problem of phantom read
• Will lead to a lot of timeouts and lock contention issues
  open A transaction
  can not add or delete the operation of the open transaction B