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Parameter Management

Oracle RAC Cluster Tips by Burleson Consulting

This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters.  To get immediate access to the code depot of working RAC scripts, buy it directly from the publisher and save more than 30%.


When the Oracle server starts up, it uses a file that contains initialization parameters. These parameters specify the name of the database, the amount of memory to allocate, the names of control files, and various limits and other system parameters.  In Oracle Database 10g, the initialization files can be replaced with an SPFILE, which allows many Oracle parameters to be changed dynamically.

Overview

Initialization parameters control the configuration of the database system. They are the key directives to start and manage any instance in the database. While launching the database instance, parameters are specified and they remain until the instance is shutdown. Optionally, certain parameters can be modified during the instance run time by the ALTER SYSTEM SET method, provided the instance has been started with the SPFILE method.

Before Oracle9i, Oracle instances were always started using a text file called an init.ora. This file is located by default in the $ORACLE_HOME/dbs directory. In Oracle9i, the server parameter file (SPFILE) was introduced. An SPFILE is a binary file stored on the database server. The Oracle Database 10g instance can be started using either the SPFILE or an init.ora file.

The SPFILE feature allows the change of parameter values dynamically. It also allows them to be set either permanently or in memory only. For Oracle Real Application Clusters (RAC), one server parameter file can be used and shared among instances. The usage of a single copy of the SPFILE for the entire database provides administrative convenience and simplification.

Many important values are specified by the initialization parameters, some of which include:

* The Global Database Name (db_name)

* Control Files name and location

* Database Block Sizes

* Initialization Parameters that affect the size of the SGA

* Maximum Number of Processes

* Method of Undo Space Management

* License Parameters

RAC and Initialization Parameters

The RAC system is a multi-instance single database system, and in general each of the instances can have its own parameter values. But certain parameters are common, such as db_name, etc. Since the RAC system can function on nodes that utilize different resources, such as CPUs and memory, database administrators can set appropriate values for the SGA configuration. Those values need not be the same for all the nodes and its instances. At the same time, there are certain parameters that are unique to each of the cluster instances.

There are three types of initialization parameters in the Real Application Clusters environment:

* Parameters That Must Be Identical Across All Instances

* Parameters That Must Be Unique Across All Instances

* Multi-Valued Parameters

Identical Parameters (Across Instances)

These parameters are generally critical directives. Some are specified at the time of database creation, and some are specified (or modified) while the RAC system is running. They must always be common in order for the clustered instances to function.

Table 8.1 shows parameters that must be identical across all the instances. For example, since RAC is a single database with multiple instances, it must have a single parameter to show the maximum number of data files for the database. This is explained in more detail in the Oracle Database 10g Database Reference Manual. These parameters indicate the fact that there is a single database, even though access is through multiple instances. The parameters, which need to be common, are mostly database-level parameters.

PARAMETER

DESCRIPTION

active_instance_count

Designates one instance in a two-instance cluster as the primary instance, and the other as the secondary instance. This parameter has no functionality in a cluster with more than two instances.

archive_lag_target

Specifies a log switch after a user-specified time period elapses.

cluster_database

Specifies whether or not Oracle Database 10g RAC is enabled.

cluster_database_ instances

Equal to the number of instances. Oracle uses the value of this parameter to compute the default value of the large_pool_size parameter when the parallel_automatic_tuning parameter is set to true.

cluster_interconnects

Specifies the additional cluster interconnects available for use in RAC environment. Oracle uses information from this parameter to distribute traffic among the various interfaces.

compatible

This parameter specifies the release with which the Oracle server must maintain compatibility.

control_files

Specifies one or more names of control files.

db_block_size

Specifies the size (in bytes) of Oracle database blocks.

db_domain

In a distributed database system, db_domain specifies the logical location of the database within the network structure.

db_files

Specifies the maximum number of database files that can be opened for this database.

db_name

Specifies a database identifier. It must correspond to the name specified in the create database statement.

dml_locks (if 0, same on all)

They can be different if the dml_locks are positive.

gc_files_to_locks

Controls the mapping of pre-release 9.0.1 parallel cache management (PCM) locks to data files.

license_max_users

Specifies the maximum number of users you can create in the database.

max_commit_ propagation_delay

Specifies the maximum amount of time allowed until the system change number (SCN), held in the SGA of an instance, and is refreshed by the log writer process (LGWR). It determines whether the local SCN should be refreshed from the lock value when getting the snapshot SCN for a query. Units are in hundredths of seconds.

parallel_execution_ message_size

Specifies the size of messages for parallel execution (formerly referred to as parallel query, PDML, Parallel Recovery, and replication).

parallel_max_servers

Specifies the maximum number of parallel execution processes and parallel recovery processes for an instance.

remote_login_ passwordfile

Specifies whether Oracle checks for a password file and how many databases can use the password file.

row_locking

Specifies whether row locks are acquired during update operations.

spfile

The value of this parameter is the name of the current server parameter file (SPFILE) in use. This parameter can be defined in a client side PFILE to indicate the name of the server parameter file to use.

trace_enabled

Controls tracing of the execution history, or code path; Oracle Support Services uses this information for debugging. When trace_enabled is set to true, Oracle records information in specific files when errors occur.

undo_management

Specifies which undo space management mode the system should use. When set to AUTO, the instance starts in automatic undo management mode. In manual undo management mode, undo space is allocated externally as rollback segments.

undo_retention

Specifies (in seconds) the amount of committed undo information to retain in the database. You can use undo_retention to satisfy queries that require old undo information in order to rollback changes to produce older images of data blocks. You can set the value at instance startup.

Table 8.1: Parameters that should remain identical among the instances

Unique Parameters (across instances)

The next category of parameters uniquely identifies a particular instance. They specify the identifiers of the independent instance, and give independent characteristics to an instance. Table 8.2 shows these parameters, which need to be unique in the cluster.

PARAMETER

DESCRIPTION

instance_name

Specifies the unique name of this instance.

instance_number

Specifies a unique number that maps the instance to one free list group for each database object created with storage parameter freelist groups.

rollback_ segments

Allocates one or more rollback segments by name to this instance.

thread

Specifies the number of the redo thread to be used by an instance.

undo_tablespace

Specifies the undo tablespace to be used when an instance starts up. If this parameter is specified when the instance is in manual undo management mode, an error will occur and startup will fail.

Table 8.2: Parameters Unique for each of the instances

 


This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters, Rampant TechPress, by Mike Ault and Madhu Tumma.

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.

http://www.rampant-books.com/book_2004_1_10g_grid.htm


 

 
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