It's a warning, not an error.
Either the CPUs are overloaded and not able to execute the block transfer quickly enough
OR --- more likely
the interconnect is not fast enough and/or erroring and resending packets.
Hemant K Chitale
This alert is server generated alert, means the DB triggers the alert and EM just receives and displays it.
If there is no "GC wait" event reporting in AWR Top 5 wait events or If you are not facing any performance issue. These alert can be ignore safely....
You can disable/change the thresholds value of this Metric to reduce the frequency of this OEM alert under below navigation for each instance of RAC
1) From EM console => Navigate to CLFDB_CLFDB2 DB home page => oracle database => monitoring => Metrics and collection settings => locate "Global Cache Statistics"
2) Change the value
2) Save the changes.
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It can be beneficial to look at V$SYSSTAT for the statistic "global cache cr blocks received". If you have a low number of blocks being transferred across the cluster interconnect, then a high value for the average get time can be indicative of a slow private network. (it is private, right?).
If you have a high value for the blocks received, then your application may be relying on to much cross-instance Cache Fusion traffic. Application partitioning can help this if you have multiple applications