a connection to an XA resource manager is open. When the transaction manager restarts, it reads the transaction manager log file and re-establishes the connection to the XA resource manager by calling xa_open_entry. It then initiates XA recover by calling xa_recover_entry.Hot recovery. Hot recovery is performed if the transaction manager remains up while the connection between the transaction manager and the XA resource manager fails because the XA resource manager or the network fails. After the failure, the transaction manager periodically calls xa_open_entry to reconnect to the XA resource manager. When the connection is reestablished, the transaction manager initiates XA recovery by calling xa_recover_entry.
总结：
XA事务没有什么神秘的地方，二阶段提交也是一个人们很自然的一个处理方式。
只不过，这个是规范，如果有多个资源之间要协调，而且都支持XA事务，那么会比较方便 。
参考：
The XA Specification 可以从这里下载到：http://download.csdn.net/detail/hengyunabc/6940529
http://en.wikipedia.org/wiki/Two-phase_commit_protocol
http://www.infoq.com/cn/articles/xa-transactions-handle
http://java.sun.com/javaee/technologies/jta/index.jsp