The session is looking for a consistent read version of data but cannot find it in the local cache. The local instance has made a request to other RAC instances for the data and is waiting on its return. Solutions Collect more information about the average time the instances are waiting for this type of request: select b1.inst_id, b2.value 'GCS CR BLOCKS RECEIVED', b1.value 'GCS CR BLOCK RECEIVE TIME', ((b1.value / b2.value) * 10) 'AVG CR BLOCK RECEIVE TIME (ms)' from gv$sysstat b1, gv$sysstat b2 where b1.name = 'global cache cr block receive time' and b2.name = 'global cache cr blocks received' and b1.inst_id = b2.inst_id; If the average cr block receive time is more than 15 milliseconds, this implies the session is waiting excessively for the block request to be satisfied by other instances. If the average time is less, that implies an excessive amount of block requests are occurring.
本文转自maclean_007 51CTO博客，原文链接:http://blog.51cto.com/maclean/1277928
