ORA-00020 and ASM
SYMPTOMS
An ASM instance complains of
ORA-00020: maximum number of processes (n) exceeded
CAUSE
The Oracle parameter PROCESSES has been exceeded as a result of multiple database instances connecting to the ASM instance
The default value (often 40) is insufficient to support more than one database connecting to the ASM instance
SOLUTION
Increase the PROCESSES parameter in the ASM parameter file
Processes = 25 + 15n, where n is the number of instances on the box using ASM for their storage.
NOTE : this formula is for a basic instance and does not accommodate for
* Multiple ARCH processes
* Multiple LGWR processes
Should the ORA-20 occur even after implementing this formula … add additional for any multiples of these background processes
More details about this calculation are available in the NOTE 265633.1 “ASM Technical Best Practices”
For 11.2 set up, the formula is PROCESSES = 50 + 50*n
where n is the number database instances connecting to the Oracle ASM instance.
This is in the standard document
https://docs.oracle.com/cd/E11882_01/server.112/e18951/asminst.htm#OSTMG94080
For 12c set up, the formulas are
For n < 10, PROCESSES = 50*n + 50
For n >= 10, PROCESSES = 10*n + 450
This is in the standard document
https://docs.oracle.com/database/121/OSTMG/GUID-3C096558-27B8-4EAF-A61C-892CBDD7E7F7.htm
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