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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: 

SET @@SESSION. var_name  = value ; SET SESSION var_name  = value ; SET var_name  = value ; SET @@ var_name  = 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 : 

•To set the session isolation level, use any of these syntaxes: 

SET @@SESSION.transaction_isolation = value ; SET SESSION transaction_isolation = value ; 

