ORA-12850: Could not allocate slaves on instances
ORA-12850: Could not allocate slaves on all specified instances : 2 needed , 0(Zero) allocated
Cause
There is a new feature in 12C called “Automatic Report Capturing Feature”. As part of this feature, some monitoring SQLs are executed by MMON_SLAVE to identify the resource-intensive SQLs and generate the SQL Monitoring report automatically for those SQLs. Those SQLs consume little more CPU and it is expected behavior being a new feature. Such monitoring queries can be identified from (G)V$SQLSTATS.
However, If the CPU consumption is significantly high then it is not an expected behavior and could be due to optimizer choosing suboptimal plan for the SQL statements.
This can happen due to Adaptive Optimization, a new feature in 12c.
Complete alert from OEM server
Host=exdbnode01
Target type=Database Instance
Target name=ORCL
Categories=Fault
Message=1 distinct types of ORA- errors have been found in the alert log.
Severity=Warning
Event reported time=Nov 17, 2016 12:04:14 PM GMT
Operating System=Linux
Platform=x86_64
Event Type=Metric Alert
Event name=alertLogStatus:genericErrors
Notification Count=1
Metric Group=Alert Log Error Status
Metric=Generic Alert Log Error Status
Metric value=1
Actions to be taken:
There is no Impact to any Running services or Applications due this Error, hence this can be ignored.
Related Support Doc:
High CPU Usage and/or Frequent Occurrences of ORA-12850 or ORA-12751 For Monitor Queries by MMON From 12.1 (Doc ID 2102131.1)Doc ID 2102131.1
See also:
Steps to generate good plan from nonPROD to PROD