Oracle RAC One Node
Oracle RAC One Node is a single instance of an Oracle RAC-enabled database running on one node in the cluster, only, under normal operations. This option adds to the flexibility that Oracle offers for database consolidation while reducing management overhead by providing a standard deployment for Oracle databases in the enterprise. Oracle RAC One Node database requires Oracle Grid Infrastructure and, therefore, requires the same hardware setup as an Oracle RAC database.
Oracle supports Oracle RAC One Node on all platforms on which Oracle RAC is certified. Similar to Oracle RAC, Oracle RAC One Node is certified on Oracle Virtual Machine (Oracle VM). Using Oracle RAC or Oracle RAC One Node with Oracle VM increases the benefits of Oracle VM with the high availability and scalability of Oracle RAC.
With Oracle RAC One Node, there is no limit to server scalability and, if applications grow to require more resources than a single node can supply, then you can upgrade your applications online to Oracle RAC. If the node that is running Oracle RAC One Node becomes overloaded, then you can relocate the instance to another node in the cluster. With Oracle RAC One Node you can use the Online Database Relocation feature to relocate the database instance with no downtime for application users. Alternatively, you can limit the CPU consumption of individual database instances per server within the cluster using Resource Manager Instance Caging and dynamically change this limit, if necessary, depending on the demand scenario.
Adding an Oracle RAC One Node Database to an Existing Cluster
1. Use the srvctl add database command to add an Oracle RAC One Node database to an existing cluster.
$ srvctl add database -dbtype RACONENODE [-server server_list] [-instance instance_name] [-timeout timeout_value]
2. When adding an administrator-managed Oracle RAC One Node database, you can optionally supply an instance prefix with the -instance instance_name option of the srvctl add database command.
3. Each service is configured by using the same value for the SERVER_POOLS attribute as the underlying database. When you add services to an Oracle RAC One Node database, srvctl configures those services using the value of the SERVER_POOLS attribute.
Converting Oracle RAC One Node to Oracle RAC
Use the srvctl add database command to add an Oracle RAC One Node database to an existing cluster. For example:
$ srvctl add database -dbtype RACONENODE [-server server_list] [-instance instance_name] [-timeout timeout_value]
Use the -server option and the -instance option when adding an administrator-managed Oracle RAC One Node database. Each service on an Oracle RAC One Node database is configured by using the same value for the SERVER_POOLS attribute as the underlying database. When you add services to an Oracle RAC One Node database, srvctl does not accept any placement information but instead configures those services using the value of the SERVER_POOLS attribute.
When adding an administrator-managed Oracle RAC One Node database, you can optionally supply an instance prefix with the -instance instance_name option of the srvctl add database command. The name of the instance will then be instance_name_1. If you do not specify an instance prefix, then the first 12 characters of the unique name of the database becomes the prefix. The instance name changes to instance_name_2 during an online database relocation and reverts to instance_name_1 during a subsequent online database relocation. The same instance name is used on failover.
Converting a RAC One Node Database to RAC
You can convert an Oracle RAC One Node database to an Oracle RAC database by logging in as the Oracle RAC One Node database owner and executing the srvctl convert database command.
srvctl convert database -db [db_unique_name] -dbtype RAC [-node [node_1]]
After you run the command, you must create server pools for each service that the database has, in addition to the database server pool. The values for SERVER_NAMES of the service server pools must be set to the node that you converted from an Oracle RAC One Node to an Oracle RAC node.
Converting an administrator-managed Oracle RAC One Node database to an Oracle RAC database sets all database services so that the single instance is preferred. After you convert the database, you can add instances by running the srvctl add instance command.
$ srvctl add instance -db [db_unique_name] -instance instance_name –node [node_2] $ srvctl add instance -db [db_unique_name] -instance instance_name –node [node_n]
Converting a policy-managed Oracle RAC One Node database to an Oracle RAC database sets all database services to UNIFORM cardinality. It also results in reusing the server pool in which the database currently runs. The conversion reconfigures the database to run on all of the nodes in the server pool. The command does not start any additional instances but running the srvctl start database command starts the database on all of the nodes in the server pool.
Example of Converting a RAC One Node Database to RAC
$ srvctl convert database -db orcl -dbtype RAC -node host01 $ srvctl add instance -db orcl –instance orcl_2 –node host02 $ srvctl start instance -db orcl -instance orcl_2
$ srvctl config database -d orcl Database unique name: orcl Database name: orcl Oracle home: /u01/app/oracle/product/12.2.0/dbhome_1 Oracle user: oracle Spfile: +DATA/orcl/spfileorcl.ora Domain: Start options: open Stop options: immediate Database role: PRIMARY Management policy: AUTOMATIC Server pools: orcl Database instances: orcl_1,orcl_2 Disk Groups: DATA,FRA Services: SERV1 Type: RAC Database is administrator managed
In the example above, the RAC One Node database ORCL is converted to an Oracle RAC database using the srvctl convert database command. The cluster consists of two nodes, host01 and host02. After the srvctl convert database command has finished executing, the second instance, orcl_2 is added to host02 using the srvctl add instance command as illustrated in the example above.
Once the instance has been added to the second node, it can be started using the srvctl start instance command. Use the srvctl config database command to verify that the database conversion and instance addition was successful.
Converting a Single Instance Database to RAC One Node (Using DBCA)
You can use DBCA to convert from single-instance Oracle databases to Oracle RAC One Node. DBCA automates the configuration of the control file attributes, creates the undo tablespaces and the redo logs, and makes the initialization parameter file entries for cluster-enabled environments. DBCA also configures Oracle Net Services, Oracle Clusterware resources, and the configuration for Oracle database management for use by Oracle Enterprise Manager or the SRVCTL utility.
Before you use DBCA to convert a single-instance database to an Oracle RAC One Node database, ensure that your system meets the following conditions:
- It is a supported hardware and operating system software configuration.
- The nodes have access to shared storage; for example, either Oracle Cluster File System or Oracle ASM is available and accessible from all nodes. On Linux on POWER systems, ensure that GPFS is available and accessible from all nodes..
- Your applications have no design characteristics that preclude their use in a clustered environment.
Oracle strongly recommends that you use the Oracle Universal Installer to perform an Oracle Database 12c installation that sets up the Oracle home and inventory in an identical location on each of the selected nodes in your cluster.
Converting a RAC Database to RAC One Node
You can convert an Oracle RAC database with one instance to an Oracle RAC One Node database using the srvctl convert database command, as follows:
srvctl convert database -db db_unique_name -dbtype RACONENODE [-instance instance_name -timeout timeout]
Prior to converting an Oracle RAC database to an Oracle RAC One Node database, you must first ensure that the Oracle RAC database has only one instance. If the Oracle RAC database is administrator-managed, then you must change the configuration of all services to set the preferred instance to the instance that you want to keep as an Oracle RAC One Node database after conversion. If any service had a PRECONNECT TAF policy, then its TAF policy must be updated to BASIC or NONE before starting the conversion process. These services must no longer have any available instance.
If the Oracle RAC database is policy managed, then you must change the configuration of all services so that they all use the same server pool before you convert the Oracle RAC database to an Oracle RAC One Node database.