Server System Variables SET_VAR  Hint Applies No Type Enumeration Default Value REPEATABLE-READ Valid Values READ-UNCOMMITTED READ-COMMITTED REPEATABLE-READ SERIALIZABLE The transaction isolation level. The default is  REPEATABLE-READ . The transaction isolation level has three scopes: global, session, and next transaction. This three-scope implementation leads to some nonstandard isolation-level assignment semantics, as described later. To set the global transaction isolation level at startup, use the  --transaction-isolation  server option. At runtime, the isolation level can be set directly using the  SET  statement to assign a value to the transaction_isolation  system variable, or indirectly using the  SET TRANSACTION  statement. If you set  transaction_isolation  directly to an isolation level name that contains a space, the name should be enclosed within quotation marks, with the space replaced by a dash. For example, use this SET  statement to set the global value: SET GLOBAL transaction_isolation = ’READ-COMMITTED’; Setting the global  transaction_isolation  value sets the isolation level for all subsequent sessions. Existing sessions are unaffected. To set the session or next-level  transaction_isolation  value, use the  SET  statement. For most session system variables, these statements are equivalent ways to set the value: As mentioned previously, the transaction isolation level has a next-transaction scope, in addition to the global and session scopes. To enable the next-transaction scope to be set,  SET  syntax for assigning session system variable values has nonstandard semantics for  transaction_isolation : SET @@SESSION.transaction_isolation =  value ; SET SESSION transaction_isolation =  value ; 910 •To set the session isolation level, use any of these syntaxes: SET @@SESSION. var_name  =  value ; SET SESSION  var_name  =  value ; SET  var_name  =  value ; SET @@ var_name  =  value ;