Multiple OC4J instances

Question

What is the difference between
1) Creating two OC4J instances on the same host and deploying the same application
on both with the same URL context
2) Creating one OC4J instance on one host with two processes

Answer 1

2) Creating one OC4J instance on one host with twoprocesses
m_yasin, can you explain how you plan to do that?
Inside of the Enterprise Manager which comes with OracleAS, there's a "Create OC4J Instance" button. You can click that and create a new OC4J instance with a name of your choosing.
With the multiple process model you have one set ofconfiguration files to maintain. So
arguably the onus on management/config is less.If you have one set of configuration files, then when
you start oc4j, you have to at least specify
different port for each of those multiple process.
Can it be/is it done by oracle AS automatically
behind the scene? OracleAS automatically takes care of it for you -- the OPMN component of OracleAS is responsible for starting (and ongoing monitoring) of processes -- it will allocate a unique set of ports to each instance it manages.
If you look in the $ORACLE_HOME/opmn/conf/opmn.xml file, you will see that where there is an entry for an OC4J instance, you will see a number of sub elements which effectively define a protocol and a port range to use for that protocol. OPMN will select a free value from this range (starting from the lower bound) and assign to each process it starts.
If you are using OC4J standalone and manually starting each instance, then you need to adjust the ports in one of the instances so that there are no collisions. This is done using the XML files in the j2ee/home/config directory.
>
I have been trying to collect any advantage and
disadvantage of start two oc4j processes with one
oc4j configuration. However, I would like to know
first if this is a supported configuration of AS.Yes its fully supported with OracleAS -- the documentation clearly covers it.
To start multiple-processes from one configuration file, you can either edit the opmn.xml file and specify a value >1 for the num_procs element inside of relecant OC4J instance's process-type configuration or you can do the same thing by entering a value >1 against the "The Number of Java Virtual Machines'" configuration setting inside of Enterprise Manager.
cheers
-steve-