Occurs when a parallel slave is waiting for data from another slave. Investigate why the other slaves are not sending data fast enough. This is normally considered an idle event, but can cause excessive CPU in some cases.
Solution
Reduce the degree of parallelism in the query.
本文转自maclean_007 51CTO博客，原文链接:http://blog.51cto.com/maclean/1277875
