By default, most parameters are set to a default value and this value is the same across all instances. However, many initialization parameters can also have different values on different instances as described in Table 3-3. Other parameters must either be unique or identical as described in the following sections
Parameters That Must Have Identical Settings on All Instances
Parameters That Should Have Identical Settings on All Instances
Table 3-3 summarizes the initialization parameters used specifically for Oracle RAC databases.
See Also:
Oracle Database Reference for additional information about these and other initialization parameters
Table 3-3 Initialization Parameters Specific to Oracle RAC
Parameter | Description |
---|---|
ACTIVE_INSTANCE_COUNT |
This initialization parameter was deprecated in Oracle RAC 11g release 2 (11.2). Instead, use a service with one preferred and one available instance. |
ASM_PREFERRED_READ_FAILURE_GROUPS |
Specifies a set of disks to be the preferred disks from which to read mirror data copies. The values you set for this parameter are instance specific and need not be the same on all instances. |
CLUSTER_DATABASE |
Enables a database to be started in cluster mode. Set this parameter to |
CLUSTER_DATABASE_INSTANCES |
Oracle RAC uses this parameter to allocate adequate memory resources. It must be set to the same value on all instances.
You can set this parameter to a value that is greater than the current number of instances, if you are planning to add instances. For policy-managed databases, you should set this parameter to a higher value only if you intend to run a database with more than 16 instances. In this case, set the parameter to the expected maximum number of instances on which this database will run. |
CLUSTER_INTERCONNECTS |
Specifies an alternative cluster interconnect for the private network when there are multiple interconnects. Notes:
|
DB_NAME |
If you set a value for |
DISPATCHERS |
Set the Oracle recommends that you configure at least the See Also: Oracle Database Net Services Administrator's Guide for complete information about configuring the |
GCS_SERVER_PROCESSES |
This static parameter specifies the initial number of server processes for an Oracle RAC instance's Global Cache Service (GCS). The GCS processes manage the routing of interinstance traffic among Oracle RAC instances. The default number of GCS server processes is calculated based on system resources with a minimum setting of 2. For systems with one CPU, there is one GCS server process. For systems with two to eight CPUs, there are two GCS server processes. For systems with more than eight CPUs, the number of GCS server processes equals the number of CPUs divided by 4, dropping any fractions. For example, if you have 10 CPUs, then 10 divided by 4 means that your system has 2 GCS processes. You can set this parameter to different values on different instances. |
INSTANCE_NAME |
Specifies the unique name of an instance. Clients can use this name to force their session to be connected to a specific instance in the cluster. The format of the Note: In Grid Plug and Play environments, the |
RESULT_CACHE_MAX_SIZE |
In a clustered database, you can either set
If you do not set the |
SERVICE_NAMES |
When you use services, Oracle recommends that you do not set a value for the Note: Oracle recommends that client connections use services rather than instance names. Entries in the |
SPFILE |
When you use an SPFILE, all Oracle RAC database instances must use the SPFILE and the file must be on shared storage. |
THREAD |
Specifies the number of the redo threads to be used by an instance. You can specify any available redo thread number if that thread number is enabled and is not used. If specified, this parameter must have unique values on all instances. The best practice is to use the |
Certain initialization parameters that are critical at database creation or that affect certain database operations must have the same value for every instance in an Oracle RAC database. Specify these parameter values in the SPFILE or in the individual PFILEs for each instance. The following list contains the parameters that must be identical on every instance:
COMPATIBLE
CLUSTER_DATABASE
CONTROL_FILES
DB_BLOCK_SIZE
DB_DOMAIN
DB_FILES
DB_NAME
DB_RECOVERY_FILE_DEST
DB_RECOVERY_FILE_DEST_SIZE
DB_UNIQUE_NAME
INSTANCE_TYPE
(RDBMS or ASM)PARALLEL_EXECUTION_MESSAGE_SIZE
REMOTE_LOGIN_PASSWORDFILE
UNDO_MANAGEMENT
The following parameters must be identical on every instance only if the parameter value is set to zero:
When it is necessary to set parameters that have unique settings on a policy-managed database, you can ensure that instances always use the same name on particular nodes by running the srvctl modify instance -n
node_name
-i
instance_name
command for each server that can be assigned to the database's server pool. Then a unique value of the parameter can be specified for instance_name
that is used whenever the database runs on node_name
.
Specify the ORACLE_SID
environment variable, which consists of the database name and the number of the INSTANCE_NAME
assigned to the instance.
Use the CLUSTER_INTERCONNECTS
initialization parameter to specify an alternative interconnect to the one Oracle Clusterware is using for the private network. Each instance of the Oracle RAC database gets a unique value when setting the CLUSTER_INTERCONNECTS
initialization parameter.
See Also:
"Administering Multiple Cluster Interconnects on Linux and UNIX Platforms" for more information about the CLUSTER_INTERCONNECTS
initialization parameter
Oracle Database uses the INSTANCE_NUMBER
parameter to distinguish among instances at startup and the INSTANCE_NAME
parameter to assign redo log groups to specific instances. The instance name can take the form db_unique_name_instance_number
and when it has this form of name and number separated by an underscore, the number after the underscore is used as the INSTANCE_NUMBER
. With Oracle Database 11.2 using Grid Plug and Play, you no longer have to explicitly assign instance numbers for policy-managed databases and the instance name defaults to db_unique_name_instance_number
, where Oracle Database assigns the instance number.
When you specify UNDO_TABLESPACE
with automatic undo management enabled, then set this parameter to a unique undo tablespace name for each instance.
If you use the ROLLBACK_SEGMENTS
parameters, then Oracle recommends setting unique values for it by using the SID
identifier in the SPFILE. However, you must set a unique value for INSTANCE_NUMBER
for each instance and you cannot use a default value.
Using the ASM_PREFERRED_READ_FAILURE_GROUPS
initialization parameter, you can specify a list of preferred read failure group names. The disks in those failure groups become the preferred read disks. Thus, every node can read from its local disks. This results in higher efficiency and performance and reduced network traffic. The setting for this parameter is instance-specific, and the values need not be the same on all instances.
Oracle recommends that you set the values for the parameters in Table 3-4 to the same value on all instances. Although you can have different settings for these parameters on different instances, setting each parameter to the same value on all instances simplifies administration.
Table 3-4 Parameters That Should Have Identical Settings on All Instances
Parameter | Description |
---|---|
ARCHIVE_LAG_TARGET |
Different values for instances in your Oracle RAC database are likely to increase overhead because of additional automatic synchronization performed by the database processing. When using either Oracle Streams downstream capture or Oracle GoldenGate integrated capture mode in a downstream capture configuration with your Oracle RAC database, the value must be greater than zero. See Also: Oracle Streams Replication Administrator's Guide for more information about downstream capture configuration |
CLUSTER_DATABASE_INSTANCES |
While it is preferable for this parameter to have identical settings across all Oracle RAC database instances, it is not required. |
LICENSE_MAX_USERS |
Because this parameter determines a database-wide limit on the number of users defined in the database, it is useful to have the same value on all instances of your database so you can see the current value no matter which instance you are using. Setting different values may cause Oracle Database to generate additional warning messages during instance startup, or cause commands related to database user management to fail on some instances. |
LOG_ARCHIVE_FORMAT |
If you do not use the same value for all your instances, then you unnecessarily complicate media recovery. The recovering instance expects the required archive log file names to have the format defined by its own value of Databases that support Oracle Data Guard, either to send or receive archived redo log files, must use the same value of |
SPFILE |
If this parameter does not identify the same file to all instances, then each instance may behave differently and unpredictably in fail over, load-balancing, and during normal operations. Additionally, a change you make to the SPFILE with an If the SPFILE values are different in instances for which the values were set by the server, then you should restart the instances that are not using the default SPFILE. |
TRACE_ENABLED |
If you want diagnostic trace information to be always available for your Oracle RAC database, you must set |
UNDO_RETENTION |
By setting different values for |