XA Transactions At runtime, characteristics at the global, session, and next-transaction scope levels can be set indirectly using the  SET TRANSACTION  statement, as described previously. They can also be set directly using the  SET  statement to assign values to the  transaction_isolation  and  transaction_read_only system variables: • SET TRANSACTION  permits optional  GLOBAL  and  SESSION  keywords for setting transaction characteristics at different scope levels. •The  SET  statement for assigning values to the  transaction_isolation  and transaction_read_only  system variables has syntaxes for setting these variables at different scope levels. The following tables show the characteristic scope level set by each  SET TRANSACTION  and variable- assignment syntax. It is possible to check the global and session values of transaction characteristics at runtime: Support for XA transactions is available for the  InnoDB  storage engine. The MySQL XA implementation is based on the X/Open CAE document  Distributed Transaction Processing: The XA Specification . This document is published by The Open Group and available at http://www.opengroup.org/public/pubs/catalog/ 13.3.8 XA Transactions Table 13.10 SET Syntax for Transaction Characteristics Table 13.9 SET TRANSACTION Syntax for Transaction Characteristics 2734 SELECT @@GLOBAL.transaction_isolation, @@GLOBAL.transaction_read_only; SELECT @@SESSION.transaction_isolation, @@SESSION.transaction_read_only; Syntax Affected Characteristic Scope SET GLOBAL TRANSACTION transaction_characteristic Global SET SESSION TRANSACTION transaction_characteristic Session SET TRANSACTION transaction_characteristic Next transaction only Syntax Affected Characteristic Scope SET GLOBAL  var_name  =  value Global SET @@GLOBAL. var_name  =  value Global SET PERSIST  var_name  =  value Global SET @@PERSIST. var_name  =  value Global SET PERSIST_ONLY  var_name  =  value No runtime effect SET @@PERSIST_ONLY. var_name  =  value No runtime effect SET SESSION  var_name  =  value Session SET @@SESSION. var_name  =  value Session SET  var_name  =  value Session SET @@ var_name  =  value Next transaction only