SET TRANSACTION Statement See Section 8.11.1, “Internal Locking Methods” , for more information on locking policy. 13.3.7 SET TRANSACTION Statement SET [GLOBAL | SESSION] TRANSACTION transaction_characteristic  [,  transaction_characteristic ] ... transaction_characteristic : { ISOLATION LEVEL  level |  access_mode } level : { REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED | SERIALIZABLE } access_mode : { READ WRITE | READ ONLY } This statement specifies transaction characteristics. It takes a list of one or more characteristic values separated by commas. Each characteristic value sets the transaction isolation level or access mode. The isolation level is used for operations on  InnoDB  tables. The access mode specifies whether transactions operate in read/write or read-only mode. In addition,  SET TRANSACTION  can include an optional  GLOBAL  or  SESSION  keyword to indicate the scope of the statement. To set the transaction isolation level, use an  ISOLATION LEVEL  level  clause. It is not permitted to specify multiple  ISOLATION LEVEL  clauses in the same  SET TRANSACTION  statement. The default isolation level is  REPEATABLE READ . Other permitted values are  READ COMMITTED ,  READ UNCOMMITTED , and  SERIALIZABLE . For information about these isolation levels, see Section 15.7.2.1, “Transaction Isolation Levels” . •Transaction Isolation Levels •Transaction Access Mode •Transaction Characteristic Scope To set the transaction access mode, use a  READ WRITE  or  READ ONLY  clause. It is not permitted to specify multiple access-mode clauses in the same  SET TRANSACTION  statement. By default, a transaction takes place in read/write mode, with both reads and writes permitted to tables used in the transaction. This mode may be specified explicitly using  SET TRANSACTION  with an access mode of  READ WRITE . If the transaction access mode is set to  READ ONLY , changes to tables are prohibited. This may enable storage engines to make performance improvements that are possible when writes are not permitted. Transaction Isolation Levels Transaction Access Mode 2732