1 Preparing for Oracle Streams Replication

Common Reasons to Use Oracle Streams Replication

The following are some of the most common reasons for using Oracle Streams replication:

• Availability: Replication provides fast, local access to shared data because it balances activity over multiple sites. Some users can access one server while other users access different servers, thereby reducing the load at all servers. Also, users can access data from the replication site that has the lowest access cost, which is typically the site that is geographically closest to them.

• Performance and Network Load Reduction: Replication provides fast, local access to shared data because it balances activity over multiple sites. Some users can access one server while other users access different servers, thereby reducing the load at all servers. Applications can access various regional servers instead of accessing one central server. This configuration can reduce network load dramatically.

Rules in an Oracle Streams Replication Environment

A rule is a database object that enables a client to perform an action when an event occurs and a condition is satisfied. Rules are evaluated by a rules engine, which is a built-in part of Oracle Database. Rules control the information flow in an Oracle Streams replication environment. Each of the following components is a client of the rules engine:

• Capture process

• Synchronous capture

• Propagation

• Apply process

You control the behavior of each of these Oracle Streams clients using rules. A rule set contains a collection of rules. You can associate a positive and a negative rule set with a capture process, a propagation, and an apply process, but a synchronous capture can have only a positive rule set.

In a replication environment, an Oracle Streams client performs an action if a logical change record (LCR) satisfies its rule sets. In general, an LCR satisfies the rule sets for an Oracle Streams client if no rules in the negative rule set evaluate to TRUE for the LCR, and at least one rule in the positive rule set evaluates to TRUE for the LCR. If an Oracle Streams client is associated with both a positive and negative rule set, then the negative rule set is always evaluated first.

Specifically, you control the information flow in an Oracle Streams replication environment in the following ways:

• Specify the changes that a capture process captures from the redo log or discards. That is, if a change found in the redo log satisfies the rule sets for a capture process, then the capture process captures the change. If a change found in the redo log does not satisfy the rule sets for a capture process, then the capture process discards the change.

• Specify the changes that a synchronous capture captures or discards. That is, if a DML change made to a table satisfies the rule set for a synchronous capture, then the synchronous capture captures the change. If a DML change made to a table does not satisfy the rule set for a synchronous capture, then the synchronous capture discards the change.

• Specify the LCRs that a propagation propagates from one queue to another or discards. That is, if an LCR in a queue satisfies the rule sets for a propagation, then the propagation sends the LCR. If an LCR in a queue does not satisfy the rule sets for a propagation, then the propagation discards the LCR.

• Specify the LCRs that an apply process dequeues or discards. That is, if an LCR in a queue satisfies the rule sets for an apply process, then the apply process dequeues and processes the LCR. If an LCR in a queue does not satisfy the rule sets for an apply process, then the apply process discards the LCR.

You can use the Oracle-supplied PL/SQL package DBMS_STREAMS_ADM to create rules for an Oracle Streams replication environment. You can specify these system-created rules at the following levels:

• Table level - Contains a rule condition that evaluates to TRUE for changes made to a particular table

• Schema level - Contains a rule condition that evaluates to TRUE for changes made to a particular schema and the database objects in the schema

• Global level - Contains a rule condition that evaluates to TRUE for all changes made to a database

In addition, a single system-created rule can evaluate to TRUE for DML changes or for DDL changes, but not both. So, for example, to replicate both DML and DDL changes to a particular table, you need both a table-level DML rule and a table-level DDL rule for the table.

Oracle Streams also supports subsetting of table data with subset rules. If a replicated table in a database contains only a subset of the data, then you can configure Oracle Streams so that only the appropriate subset of the data is replicated. For example, a particular database might maintain data for employees in a particular department only. One or more other databases in the replication environment might contain all of the data in the employees table. In this case, you can use subset rules to replicate changes to the data for employees in that department with the subset table, but not changes to employees in other departments.

Subsetting can be done at any point in the Oracle Streams information flow. That is, a capture process or synchronous capture can use a subset rule to capture a subset of changes to a particular table, a propagation can use a subset rule to propagate a subset of changes to a particular table, and an apply process can use a subset rule to apply a subset of changes to a particular table.

Decide Which Type of Replication Environment to Configure

Before configuring a replication environment, first decide how many databases will be included in the replication environment, which database objects will be replicated, and how database changes will flow through the replication environment. Here are the most common types of replication environments:

• One-way replication in a two database environment where one database is read/write and the other database is read-only

• Bi-directional replication in a two database environment where both databases are read/write

• Hub-and-spoke replication with a read/write hub and read-only spokes

• Hub-and-spoke replication with a read/write hub and one or more read/write spokes

• N-way replication with multiple read/write databases

One of these environments meet the replication requirements of most organizations. Oracle Database 2 Day + Data Replication and Integration Guide describes these common types of replication environments in detail.

If these common replication environments do not meet your requirements, then you can configure almost any type of custom replication environment with Oracle Streams. For example, a custom replication environment might send database changes through several intermediary databases before the changes are applied at a destination database.

Decide Whether to Configure Local or Downstream Capture for the Source Database

Local capture means that a capture process runs on the source database. Downstream capture means that a capture process runs on a database other than the source database. The primary reason to use downstream capture is to reduce the load on the source database, thereby improving its performance.

The database that captures changes made to the source database is called the capture database. One of the following databases can be the capture database:

• Source database (local capture)

• Destination database (downstream capture)

• A third database (downstream capture)

Figure 1-2 shows the role of the capture database.

Figure 1-2 The Capture Database

Description of "Figure 1-2 The Capture Database"

If the source database or a third database is the capture database, then a propagation sends changes from the capture database to the destination database. If the destination database is the capture database, then this propagation between databases is not needed because the capture process and apply process use the same queue.

If you decide to configure a downstream capture process, then you must decide which type of downstream capture process you want to configure. The following types are available:

• A real-time downstream capture process configuration means that redo transport services use the log writer process (LGWR) at the source database to send redo data to the downstream database, and a remote file server process (RFS) at the downstream database receives the redo data over the network and stores the redo data in the standby redo log.

• An archived-log downstream capture process configuration means that archived redo log files from the source database are copied to the downstream database, and the capture process captures changes in these archived redo log files. These log files can be transferred automatically using redo transport services, or they can be transferred manually using a method such at FTP.

The advantage of real-time downstream capture over archived-log downstream capture is that real-time downstream capture reduces the amount of time required to capture changes made at the source database. The time is reduced because the real-time downstream capture process does not need to wait for the redo log file to be archived before it can capture changes from it. You can configure multiple real-time downstream capture processes that captures changes from the same source database, but you cannot configure real-time downstream capture for multiple source databases at one downstream database.

The advantage of archived-log downstream capture over real-time downstream capture is that archived-log downstream capture allows downstream capture processes from multiple source databases at a downstream database. You can copy redo log files from multiple source databases to a single downstream database and configure multiple archived-log downstream capture processes to capture changes in these redo log files.

If you decide to configure a real-time downstream capture process, then you must complete the steps in "Configuring Log File Transfer to a Downstream Capture Database" and "Adding Standby Redo Logs for Real-Time Downstream Capture".

If you decide to configure an archived-log downstream capture process that uses archived redo log files that were transferred to the downstream database automatically by redo transport services, then you must complete the steps in "Configuring Log File Transfer to a Downstream Capture Database".

Decide Whether Changes Are Allowed at One Database or at Multiple Databases

A replication environment can limit changes to a particular replicated database object to one database only. In this case, the replicated database object is read/write at one database and read-only at the other databases in the replication environment. Or, a replication environment can allow changes to a replicated database object at two or more databases.

When two or more databases can change a replicated database object, conflicts are possible. A conflict is a mismatch between the old values in an LCR and the expected data in a table. Conflicts can occur in an Oracle Streams replication environment that permits concurrent data manipulation language (DML) operations on the same data at multiple databases. Conflicts typically result when two or more databases make changes to the same row in a replicated table at nearly the same time. If conflicts are not resolved, then they can result in inconsistent data at replica databases.

Typically, conflicts are possible in the following common types of replication environments:

• Bi-directional replication in a two database environment where the replicated database objects at both databases are read/write

• Hub-and-spoke replication where the replicated database objects are read/write at the hub and at one or more spokes

• N-way replication where the replicated database objects are read/write at multiple databases

Oracle Database 2 Day + Data Replication and Integration Guide describes these common types of replication environments in more detail.

Oracle Streams provides prebuilt conflict handlers to resolve conflicts automatically. You can also build your own custom conflict handler to resolve data conflicts specific to your business rules. Such a conflict handler can be part of a procedure DML handler or an error handler.

If conflicts are possible in the replication environment you plan to configure, then plan to create conflict handlers to resolve these conflicts.

Decide Whether the Replication Environment Will Have Nonidentical Replicas

Oracle Streams replication supports sharing database objects that are not identical at multiple databases. Different databases in the Oracle Streams environment can contain replicated database objects with different structures. In Oracle Streams replication, a rule-based transformation is any modification to a logical change record (LCR) that results when a rule in a positive rule set evaluates to TRUE. You can configure rule-based transformations during capture, propagation, or apply to make any necessary changes to LCRs so that they can be applied at a destination database.

For example, a table at a source database can have the same data as a table at a destination database, but some column names can be different. In this case, a rule-based transformation can change the names of the columns in LCRs from the source database so that they can be applied successfully at the destination database.

There are two types of rule-based transformations: declarative and custom. Declarative rule-based transformations cover a set of common transformation scenarios for row LCRs, including renaming a schema, renaming a table, adding a column, renaming a column, keeping a list of columns, and deleting a column. You specify such a transformation using a procedure in the DBMS_STREAMS_ADM package. Oracle Streams performs declarative transformations internally, without invoking PL/SQL.

A custom rule-based transformation requires a user-defined PL/SQL function to perform the transformation. Oracle Streams invokes the PL/SQL function to perform the transformation. A custom rule-based transformation can modify captured LCRs, persistent LCRs, or user messages. For example, a custom rule-based transformation can change the data type of a particular column in an LCR. A custom rule-based transformation must be defined as a PL/SQL function that takes an ANYDATA object as input and returns an ANYDATA object.

Rule-based transformations can be done at any point in the Oracle Streams information flow. That is, a capture process or a synchronous capture can perform a rule-based transformation on a change when a rule in its positive rule set evaluates to TRUE for the change. Similarly, a propagation or an apply process can perform a rule-based transformation on an LCR when a rule in its positive rule set evaluates to TRUE for the LCR.

If you plan to have nonidentical copies of database objects in your replication environment, then plan to create rule-based transformations that will modify LCRs so that they can be applied successfully at destination databases.

Decide Whether the Replication Environment Will Use Apply Handlers

When you use an apply handler, an apply process passes a message to either a collection of SQL statements or a user-created PL/SQL procedure for processing.

The following types of apply handlers are possible:

• A statement DML handler uses a collection of SQL statement to process row logical change records (row LCRs).

• A procedure DML handler uses a PL/SQL procedure to process row LCRs.

• A DDL handler uses a PL/SQL procedure to process DDL LCRs.

• A message handler uses a PL/SQL procedure to process user messages.

• A precommit handlers uses a PL/SQL procedure to process the commit information for a transaction.

• An error handler uses a PL/SQL procedure to process row LCRs that have caused apply errors.

An apply handler can process a message in a customized way. For example, a handler might audit the changes made to a table or enqueue an LCR into a queue after the change in the LCR has been applied. An application can then process the re-enqueued LCR. A handler might also be used to audit the changes made to a database.

If you must process LCRs in a customized way in your replication environment, then decide which apply handlers you should use to accomplish your goals. Next, create the PL/SQL procedures that will perform the custom processing and specify these procedures as apply handlers when your environment is configured.

Decide Whether to Maintain DDL Changes

Replication environments typically maintain data manipulation language (DML) changes to the replicated database objects. DML changes include INSERT, UPDATE, DELETE, and LOB update operations. You must decide whether you want the replication environment to maintain data definition language (DDL) changes as well. Examples of statements that result in DDL changes are CREATE TABLE, ALTER TABLE, ALTER TABLESPACE, and ALTER DATABASE.

Some Oracle Streams replication environments assume that the database objects are the same at each database. In this case, maintaining DDL changes with Oracle Streams makes it easy to keep the shared database objects synchronized. However, some Oracle Streams replication environments require that shared database objects are different at different databases. For example, a table can have a different name or shape at two different databases. In these environments, rule-based transformations and apply handlers can modify changes so that they can be shared between databases, and you might not want to maintain DDL changes with Oracle Streams. In this case, you should make DDL changes manually at each database that required them.

When replicating data definition language (DDL) changes, do not allow system-generated names for constraints or indexes. Modifications to these database objects will most likely fail at the destination database because the object names at the different databases will not match. Also, storage clauses might cause problems if the destination databases are not identical. If you decide not to replicate DDL in your Oracle Streams environment, then any table structure changes must be performed manually at each database in the environment.

Decide How to Configure the Replication Environment

There are three options for configuring an Oracle Streams replication environment:

• Run the Setup Streams Replication wizard to configure replication between two databases. You can run the wizard multiple times to configure a replication environment with more than two databases.

  The wizard walks you through the process of configuring your replication environment, but there are some limits to the types of replication environments that can be configured with the wizard. For example, the wizard currently cannot configure synchronous capture.

  See "Configuring Replication Using the Setup Streams Replication Wizard", Oracle Database 2 Day + Data Replication and Integration Guide, and the Oracle Enterprise Manager online help for more information about the replication configuration wizards.

• Run a configuration procedure in the DBMS_STREAMS_ADM supplied PL/SQL package to configure replication between two databases. You can run the procedure multiple times to configure a replication environment with more than two databases.

  The following procedures configure Oracle Streams replication:

  • The MAINTAIN_GLOBAL procedure configures an Oracle Streams environment that replicates changes at the database level between two databases.

  • The MAINTAIN_SCHEMAS procedure configures an Oracle Streams environment that replicates changes to specified schemas between two databases.

  • The MAINTAIN_SIMPLE_TTS procedure clones a simple tablespace from a source database at a destination database and uses Oracle Streams to maintain this tablespace at both databases.

  • The MAINTAIN_TABLES procedure configures an Oracle Streams environment that replicates changes to specified tables between two databases.

  • The MAINTAIN_TTS procedure clones a set of tablespaces from a source database at a destination database and uses Oracle Streams to maintain these tablespaces at both databases.

  These procedures configure multiple Oracle Streams components with a single procedure call, and they automatically follow Oracle Streams best practices. They are ideal for configuring one-way, bi-directional, and hub-and-spoke replication environments.

  See "Configuring Replication Using the DBMS_STREAMS_ADM Package" and Oracle Database PL/SQL Packages and Types Reference for more information about these procedures.

• Configure each Oracle Streams component separately. These components include queues, capture processes, synchronous captures, propagations, and apply processes. Choose this option if you plan to configure an n-way replication environment, or if you plan to configure another type of replication environment that cannot be configured with the wizards or configuration procedures.

  See Chapter 3, "Flexible Oracle Streams Replication Configuration" for information about configuring each component of a replication environment separately.

Your configuration options might be limited by the type of replication environment you want to configure. See "Decide Which Type of Replication Environment to Configure".

Table 1-1 lists the configuration options that are available for each type of replication environment.

Before configuring the replication environment, complete the tasks in "Tasks to Complete Before Configuring Oracle Streams Replication".

Configuring an Oracle Streams Administrator on All Databases

To configure and manage an Oracle Streams environment, either create a new user with the appropriate privileges or grant these privileges to an existing user. You should not use the SYS or SYSTEM user as an Oracle Streams administrator, and the Oracle Streams administrator should not use the SYSTEM tablespace as its default tablespace.

Typically, the user name for the Oracle Streams administrator is strmadmin, but any user with the proper privileges can be an Oracle Streams administrator. The examples in this section use strmadmin for the Oracle Streams administrator user name.

Create a separate tablespace for the Oracle Streams administrator at each participating Oracle Streams database. This tablespace stores any objects created in the Oracle Streams administrator schema, including any spillover of messages from the buffered queues owned by the schema.

Complete the following steps to configure an Oracle Streams administrator at each database in the environment that will use Oracle Streams:

1. In SQL*Plus, connect as an administrative user who can create users, grant privileges, and create tablespaces. Remain connected as this administrative user for all subsequent steps.

   See Oracle Database Administrator's Guide for information about connecting to a database in SQL*Plus.

2. Either create a tablespace for the Oracle Streams administrator or use an existing tablespace. For example, the following statement creates a new tablespace for the Oracle Streams administrator:

   CREATE TABLESPACE streams_tbs DATAFILE '/usr/oracle/dbs/streams_tbs.dbf' 
     SIZE 25M REUSE AUTOEXTEND ON MAXSIZE UNLIMITED;
   

3. Create a new user to act as the Oracle Streams administrator or use an existing user. For example, to create a user named strmadmin and specify that this user uses the streams_tbs tablespace, run the following statement:

   CREATE USER strmadmin IDENTIFIED BY password 
      DEFAULT TABLESPACE streams_tbs
      QUOTA UNLIMITED ON streams_tbs;
   

   Note:

   Enter an appropriate password for the administrative user.

   See Also:

   Oracle Database Security Guide for guidelines for choosing passwords

4. Grant the Oracle Streams administrator DBA role:

   GRANT DBA TO strmadmin;
   

   Note:

   The DBA role is required for a user to create or alter capture processes, synchronous captures, and apply processes. When the user does not need to perform these tasks, DBA role can be revoked from the user.

5. Run the GRANT_ADMIN_PRIVILEGE procedure in the DBMS_STREAMS_AUTH package.

   A user must have explicit EXECUTE privilege on a package to execute a subprogram in the package inside of a user-created subprogram, and a user must have explicit SELECT privilege on a data dictionary view to query the view inside of a user-created subprogram. These privileges cannot be through a role. You can run the GRANT_ADMIN_PRIVILEGE procedure to grant such privileges to the Oracle Streams administrator, or you can grant them directly.

   Depending on the parameter settings for the GRANT_ADMIN_PRIVILEGE procedure, it either grants the privileges for an Oracle Streams administrator directly, or it generates a script that you can edit and then run to grant these privileges.

   See Also:

   Oracle Database PL/SQL Packages and Types Reference for more information about this procedure

   Use the GRANT_ADMIN_PRIVILEGE procedure to grant privileges directly:

   Run the following procedure:

   BEGIN
     DBMS_STREAMS_AUTH.GRANT_ADMIN_PRIVILEGE(
       grantee          => 'strmadmin',    
       grant_privileges => TRUE);
   END;
   /
   

   Use the GRANT_ADMIN_PRIVILEGE procedure to generate a script:

   Complete the following steps:

   1. Use the SQL statement CREATE DIRECTORY to create a directory object for the directory into which you want to generate the script. A directory object is similar to an alias for the directory. For example, to create a directory object called strms_dir for the /usr/admin directory on your computer system, run the following procedure:

      CREATE DIRECTORY strms_dir AS '/usr/admin';
      

   2. Run the GRANT_ADMIN_PRIVILEGE procedure to generate a script named grant_strms_privs.sql and place this script in the /usr/admin directory on your computer system:

      BEGIN
        DBMS_STREAMS_AUTH.GRANT_ADMIN_PRIVILEGE(
          grantee          => 'strmadmin',    
          grant_privileges => FALSE,
          file_name        => 'grant_strms_privs.sql',
          directory_name   => 'strms_dir');
      END;
      /
      

      Notice that the grant_privileges parameter is set to FALSE so that the procedure does not grant the privileges directly. Also, notice that the directory object created in Step a is specified for the directory_name parameter.

   3. Edit the generated script if necessary and save your changes.

   4. Execute the script in SQL*Plus:

      SET ECHO ON
      SPOOL grant_strms_privs.out
      @/usr/admin/grant_strms_privs.sql
      SPOOL OFF
      

   5. Check the spool file to ensure that all of the grants executed successfully. If there are errors, then edit the script to correct the errors and rerun it.

6. If necessary, grant the following additional privileges:

   • If you plan to use Oracle Enterprise Manager to manage databases with Oracle Streams components, then configure the Oracle Streams administrator to be a Database Control administrator. Doing so grants additional privileges required by Oracle Enterprise Manager, such as the privileges required to run Oracle Enterprise Manager jobs. See Oracle Database 2 Day DBA for instructions.

   • Grant the privileges for a remote Oracle Streams administrator to perform actions in the local database. Grant these privileges using the GRANT_REMOTE_ADMIN_ACCESS procedure in the DBMS_STREAMS_AUTH package. Grant this privilege if a remote Oracle Streams administrator will use a database link that connects to the local Oracle Streams administrator to perform administrative actions. Specifically, grant these privileges if either of the following conditions are true:

     • You plan to configure a downstream capture process at a remote downstream database that captures changes originating at the local source database, and the downstream capture process will use a database link to perform administrative actions at the source database.

     • You plan to configure an apply process at the local database and use a remote Oracle Streams administrator to set the instantiation SCN values for replicated database objects at the local database.

   • If no apply user is specified for an apply process, then grant the Oracle Streams administrator the necessary privileges to perform DML and DDL changes on the apply objects owned by other users. If an apply user is specified, then the apply user must have these privileges. These privileges can be granted directly or through a role.

   • If no apply user is specified for an apply process, then grant the Oracle Streams administrator EXECUTE privilege on any PL/SQL subprogram owned by another user that is executed by an Oracle Streams apply process. These subprograms can be used in apply handlers or error handlers. If an apply user is specified, then the apply user must have these privileges. These privileges must be granted directly. They cannot be granted through a role.

   • Grant the Oracle Streams administrator EXECUTE privilege on any PL/SQL function owned by another user that is specified in a custom rule-based transformation for a rule used by an Oracle Streams capture process, synchronous capture, propagation, apply process, or messaging client. For a capture process or synchronous capture, if a capture user is specified, then the capture user must have these privileges. For an apply process, if an apply user is specified, then the apply user must have these privileges. These privileges must be granted directly. They cannot be granted through a role.

   • Grant the Oracle Streams administrator privileges to alter database objects where appropriate. For example, if the Oracle Streams administrator must create a supplemental log group for a table in another schema, then the Oracle Streams administrator must have the necessary privileges to alter the table. These privileges can be granted directly or through a role.

   • If the Oracle Streams administrator does not own the queue used by an Oracle Streams capture process, synchronous capture, propagation, apply process, or messaging client, and is not specified as the queue user for the queue when the queue is created, then the Oracle Streams administrator must be configured as a secure queue user of the queue if you want the Oracle Streams administrator to be able to enqueue messages into or dequeue messages from the queue. The Oracle Streams administrator might also need ENQUEUE or DEQUEUE privileges on the queue, or both. See Oracle Streams Concepts and Administration for information about managing queues.

   • Grant the Oracle Streams administrator EXECUTE privilege on any object types that the Oracle Streams administrator might need to access. These privileges can be granted directly or through a role.

   • If the Oracle Streams administrator will use Data Pump to perform export and import operations on database objects in other schemas during an Oracle Streams instantiation, then grant the EXP_FULL_DATABASE and IMP_FULL_DATABASE roles to the Oracle Streams administrator.

   • If Oracle Database Vault is installed, then the user who performs the following actions must be granted the BECOME USER system privilege:

     • Creates or alters a capture process

     • Creates or alters an apply process

     Granting the BECOME USER system privilege to the user who performs these actions is not required if Oracle Database Vault is not installed. You can revoke the BECOME USER system privilege from the user after the completing one of these actions, if necessary.

7. Repeat all of the previous steps at each database in the environment that will use Oracle Streams.

Configuring Network Connectivity and Database Links

If you plan to use Oracle Streams to share information between databases, then configure network connectivity and database links between these databases:

• For Oracle databases, configure your network and Oracle Net so that the databases can communicate with each other.

• For non-Oracle databases, configure an Oracle Database Gateway for communication between the Oracle database and the non-Oracle database.

• If you plan to propagate messages from a source queue at a database to a destination queue at another database, then create a private database link between the database containing the source queue and the database containing the destination queue. Each database link should use a CONNECT TO clause for the user propagating messages between databases.

A database link from the source database to the destination database is always required. The name of the database link must match the global name of the destination database.

A database link from the destination database to the source database is required in any of the following cases:

• The Oracle Streams replication environment will be bi-directional.

• A Data Pump network import will be performed during instantiation.

• The destination database is the capture database for downstream capture of source database changes.

• The RMAN DUPLICATE or CONVERT DATABASE command will be used for database instantiation.

  This database link is required because the POST_INSTANTIATION_SETUP procedure with a non-NULL setting for the instantiation_scn parameter runs the SET_GLOBAL_INSTANTIATION_SCN procedure in the DBMS_APPLY_ADM package at the destination database. The SET_GLOBAL_INSTANTIATION_SCN procedure requires the database link. This database link must be created after the RMAN instantiation and before running the POST_INSTANTIATION_SETUP procedure.

In each of these cases, the name of the database link must match the global name of the source database.

If a third database is the capture database for downstream capture of source database changes, then the following database links are also required:

• A database link is required from the third database to the source database. The name of the database link must match the global name of the source database.

• A database link is required from the third database to the destination database. The name of the database link must match the global name of the destination database.

Each database link should be created in the Oracle Streams administrator's schema. For example, if the global name of the source database is dbs1.example.com, the global name of the destination database is dbs2.example.com, and the Oracle Streams administrator is strmadmin at each database, then the following statement creates the database link from the source database to the destination database:

CONNECT strmadmin@dbs1.example.com
Enter password: password

CREATE DATABASE LINK dbs2.example.com CONNECT TO strmadmin 
   IDENTIFIED BY password USING 'dbs2.example.com';

If a database link is required from the destination database to the source database, then the following statement creates this database link:

CONNECT strmadmin@dbs2.example.com
Enter password: password

CREATE DATABASE LINK dbs1.example.com CONNECT TO strmadmin 
   IDENTIFIED BY password USING 'dbs1.example.com';

If a third database is the capture database, then a database link is required from the third database to the source and destination databases. For example, if the third database is dbs3.example.com, then the following statements create the database links from the third database to the source and destination databases:

CONNECT strmadmin@dbs3.example.com
Enter password: password

CREATE DATABASE LINK dbs1.example.com CONNECT TO strmadmin 
   IDENTIFIED BY password USING 'dbs1.example.com';

CREATE DATABASE LINK dbs2.example.com CONNECT TO strmadmin 
   IDENTIFIED BY password USING 'dbs2.example.com';

If an RMAN database instantiation is performed, then the database link at the source database is copied to the destination database during instantiation. This copied database link should be dropped at the destination database. In this case, if the replication is bi-directional, and a database link from the destination database to the source database is required, then this database link should be created after the instantiation.

Ensuring That Each Source Database Is In ARCHIVELOG Mode

In an Oracle Streams replication environment, each source database that generates changes that will be captured by a capture process must be in ARCHIVELOG mode. For downstream capture processes, the downstream database also must run in ARCHIVELOG mode if you plan to configure a real-time downstream capture process. The downstream database does not need to run in ARCHIVELOG mode if you plan to run only archived-log downstream capture processes on it.

If you are configuring Oracle Streams in an Oracle Real Application Clusters (Oracle RAC) environment, then the archive log files of all threads from all instances must be available to any instance running a capture process. This requirement pertains to both local and downstream capture processes.

Setting Initialization Parameters Relevant to Oracle Streams

Some initialization parameters are important for the configuration, operation, reliability, and performance of an Oracle Streams environment. Set these parameters appropriately for your Oracle Streams environment.

Table 1-2 describes the initialization parameters that are relevant to Oracle Streams. This table specifies whether each parameter is modifiable. A modifiable initialization parameter can be modified using the ALTER SYSTEM statement while an instance is running. Some modifiable parameters can also be modified for a single session using the ALTER SESSION statement.

Configuring the Oracle Streams Pool

The Oracle Streams pool is a portion of memory in the System Global Area (SGA) that is used by Oracle Streams. The Oracle Streams pool stores buffered queue messages in memory, and it provides memory for capture processes, apply processes, XStream outbound servers, and XStream inbound servers. The Oracle Streams pool always stores LCRs captured by a capture process, and it stores LCRs and messages that are enqueued into a buffered queue by applications.

The Oracle Streams pool is initialized the first time any one of the following actions occurs in a database:

• Messages are enqueued into a buffered queue.

  Oracle Streams components manipulate messages in a buffered queue. These components include capture processes, propagations, apply processes, XStream outbound servers, and XStream inbound servers. Also, Data Pump export and import operations initialize the Oracle Streams pool because these operations use buffered queues.

• Messages are dequeued from a persistent queue in a configuration that does not use Oracle Real Application Clusters (Oracle RAC).

  The Oracle Streams pool is used to optimize dequeue operations from persistent queues. The Oracle Streams pool is not used to optimize dequeue operations from persistent queues in an Oracle RAC configuration.

• A capture process is started.

• A propagation is created.

• An apply process is started.

• An XStream outbound server is started.

• An XStream inbound server is started.

The size of the Oracle Streams pool is determined in one of the following ways:

• Using Automatic Memory Management to Set the Oracle Streams Pool Size

• Using Automatic Shared Memory Management to Set the Oracle Streams Pool Size

• Setting the Oracle Streams Pool Size Manually

• Using the Default Setting for the Oracle Streams Pool Size

Specifying Supplemental Logging

When you use a capture process to capture changes, supplemental logging must be specified for certain columns at a source database for changes to the columns to be applied successfully at a destination database. Supplemental logging places additional information in the redo log for these columns. A capture process captures this additional information and places it in logical change records (LCRs), and an apply process might need this additional information to apply changes properly.

This section contains these topics:

• Required Supplemental Logging in an Oracle Streams Replication Environment

• Specifying Table Supplemental Logging Using Unconditional Log Groups

• Specifying Table Supplemental Logging Using Conditional Log Groups

• Dropping a Supplemental Log Group

• Specifying Database Supplemental Logging of Key Columns

• Dropping Database Supplemental Logging of Key Columns

• Procedures That Automatically Specify Supplemental Logging

ALTER TABLE hr.regions ADD SUPPLEMENTAL LOG DATA (PRIMARY KEY) COLUMNS;

ALTER TABLE hr.regions ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS;

ALTER TABLE hr.departments ADD SUPPLEMENTAL LOG GROUP log_group_dep_pk
  (department_id, manager_id) ALWAYS;

ALTER TABLE hr.employees ADD SUPPLEMENTAL LOG DATA 
  (UNIQUE, FOREIGN KEY) COLUMNS;

ALTER TABLE hr.jobs ADD SUPPLEMENTAL LOG GROUP log_group_jobs_cr 
  (min_salary, max_salary);

ALTER TABLE hr.jobs DROP SUPPLEMENTAL LOG GROUP log_group_jobs_cr;

ALTER DATABASE ADD SUPPLEMENTAL LOG DATA 
   (PRIMARY KEY, UNIQUE, FOREIGN KEY) COLUMNS;

ALTER DATABASE ADD SUPPLEMENTAL LOG DATA 
   (PRIMARY KEY, UNIQUE) COLUMNS;

ALTER DATABASE DROP SUPPLEMENTAL LOG DATA 
  (PRIMARY KEY, UNIQUE, FOREIGN KEY) COLUMNS;

Configuring Log File Transfer to a Downstream Capture Database

If you decided to use a local capture process at the source database, then log file transfer is not required. However, if you decided to use downstream capture that uses redo transport services to transfer archived redo log files to the downstream database automatically, then configure log file transfer from the source database to the capture database before configuring the replication environment. See "Decide Whether to Configure Local or Downstream Capture for the Source Database" for information about the decision.

You must complete the steps in this section if you plan to configure downstream capture using either of the following methods:

• Running a configuration procedure in the DBMS_STREAMS_ADM supplied PL/SQL package to configure replication between two databases

• Configuring each Oracle Streams component separately

See "Decide How to Configure the Replication Environment" for information about these methods.

Complete the following steps to prepare the source database to transfer its redo log files to the capture database, and to prepare the capture database to accept these redo log files:

1. Configure Oracle Net so that the source database can communicate with the downstream database.

   See Also:

   Oracle Database Net Services Administrator's Guide

2. Configure authentication at both databases to support the transfer of redo data.

   Redo transport sessions are authenticated using either the Secure Sockets Layer (SSL) protocol or a remote login password file. If the source database has a remote login password file, then copy it to the appropriate directory on the downstream capture database system. The password file must be the same at the source database and the downstream capture database.

   See Also:

   Oracle Data Guard Concepts and Administration for detailed information about authentication requirements for redo transport

3. At the source database, set the following initialization parameters to configure redo transport services to transmit redo data from the source database to the downstream database:

   • LOG_ARCHIVE_DEST_n - Configure at least one LOG_ARCHIVE_DEST_n initialization parameter to transmit redo data to the downstream database. Set the following attributes of this parameter in the following way:

     • SERVICE - Specify the network service name of the downstream database.

     • ASYNC or SYNC - Specify a redo transport mode.

       The advantage of specifying ASYNC is that it results in little or no effect on the performance of the source database. If the source database is running Oracle Database 10g Release 1 or later, then ASYNC is recommended to avoid affecting source database performance if the downstream database or network is performing poorly.

       The advantage of specifying SYNC is that redo data is sent to the downstream database faster then when ASYNC is specified. Also, specifying SYNC AFFIRM results in behavior that is similar to MAXIMUM AVAILABILITY standby protection mode. Note that specifying an ALTER DATABASE STANDBY DATABASE TO MAXIMIZE AVAILABILITY SQL statement has no effect on an Oracle Streams capture process.

     • NOREGISTER - Specify this attribute so that the location of the archived redo log files is not recorded in the downstream database control file.

     • VALID_FOR - Specify either (ONLINE_LOGFILE,PRIMARY_ROLE) or (ONLINE_LOGFILE,ALL_ROLES).

     • TEMPLATE - If you are configuring an archived-log downstream capture process, then specify a directory and format template for archived redo logs at the downstream database. The TEMPLATE attribute overrides the LOG_ARCHIVE_FORMAT initialization parameter settings at the downstream database. The TEMPLATE attribute is valid only with remote destinations. Ensure that the format uses all of the following variables at each source database: %t, %s, and %r.

       Do not specify the TEMPLATE attribute if you are configuring a real-time downstream capture process.

     • DB_UNIQUE_NAME - The unique name of the downstream database. Use the name specified for the DB_UNIQUE_NAME initialization parameter at the downstream database.

     The following example is a LOG_ARCHIVE_DEST_n setting that specifies the downstream database dbs2 for a real-time downstream capture process:

     LOG_ARCHIVE_DEST_2='SERVICE=DBS2.EXAMPLE.COM ASYNC NOREGISTER
        VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE)
        DB_UNIQUE_NAME=dbs2'
     

     The following example is a LOG_ARCHIVE_DEST_n setting that specifies the downstream database dbs2 for an archived-log downstream capture process:

     LOG_ARCHIVE_DEST_2='SERVICE=DBS2.EXAMPLE.COM ASYNC NOREGISTER
        VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE)
        TEMPLATE=/usr/oracle/log_for_dbs1/dbs1_arch_%t_%s_%r.log
        DB_UNIQUE_NAME=dbs2'
     

     See "Decide Whether to Configure Local or Downstream Capture for the Source Database" for information about the differences between real-time and archived-log downstream capture.

     Tip:

     If you are configuring an archived-log downstream capture process, then specify a value for the TEMPLATE attribute that keeps log files from a remote source database separate from local database log files. In addition, if the downstream database contains log files from multiple source databases, then the log files from each source database should be kept separate from each other.

   • LOG_ARCHIVE_DEST_STATE_n - Set this initialization parameter that corresponds with the LOG_ARCHIVE_DEST_n parameter for the downstream database to ENABLE.

     For example, if the LOG_ARCHIVE_DEST_2 initialization parameter is set for the downstream database, then set the LOG_ARCHIVE_DEST_STATE_2 parameter in the following way:

     LOG_ARCHIVE_DEST_STATE_2=ENABLE 
     

   • LOG_ARCHIVE_CONFIG - Set the DB_CONFIG attribute in this initialization parameter to include the DB_UNIQUE_NAME of the source database and the downstream database.

     For example, if the DB_UNIQUE_NAME of the source database is dbs1, and the DB_UNIQUE_NAME of the downstream database is dbs2, then specify the following parameter:

     LOG_ARCHIVE_CONFIG='DG_CONFIG=(dbs1,dbs2)'
     

     By default, the LOG_ARCHIVE_CONFIG parameter enables a database to both send and receive redo.

   See Also:

   Oracle Database Reference and Oracle Data Guard Concepts and Administration for more information about these initialization parameters

4. At the downstream database, set the DB_CONFIG attribute in the LOG_ARCHIVE_CONFIG initialization parameter to include the DB_UNIQUE_NAME of the source database and the downstream database.

   For example, if the DB_UNIQUE_NAME of the source database is dbs1, and the DB_UNIQUE_NAME of the downstream database is dbs2, then specify the following parameter:

   LOG_ARCHIVE_CONFIG='DG_CONFIG=(dbs1,dbs2)'
   

   By default, the LOG_ARCHIVE_CONFIG parameter enables a database to both send and receive redo.

5. If you reset any initialization parameters while the instance was running at a database in Step 3 or Step 4, then you might want to reset them in the initialization parameter file as well, so that the new values are retained when the database is restarted.

   If you did not reset the initialization parameters while the instance was running, but instead reset them in the initialization parameter file in Step 3 or Step 4, then restart the database. The source database must be open when it sends redo log files to the downstream database, because the global name of the source database is sent to the downstream database only if the source database is open.

When these steps are complete, you are ready to perform one of the following tasks:

• Configure an archived-log downstream capture process. In this case, see the instructions in the following sections:

  • "Configuring Replication Using the DBMS_STREAMS_ADM Package"

  • "Configuring an Archived-Log Downstream Capture Process"

• Add standby redo logs files at the downstream database for a real-time downstream capture process. In this case, see the instructions in "Adding Standby Redo Logs for Real-Time Downstream Capture".

Adding Standby Redo Logs for Real-Time Downstream Capture

The example in this section adds standby redo logs at a downstream database. Standby redo logs are required to configure a real-time downstream capture process. In the example, the source database is dbs1.example.com and the downstream database is dbs2.example.com

See "Decide Whether to Configure Local or Downstream Capture for the Source Database" for information about the differences between real-time and archived-log downstream capture. The steps in this section are required only if you are configuring real-time downstream capture. If you are configuring archived-log downstream capture, then do not complete the steps in this section.

Complete the following steps to add a standby redo log at the downstream database:

1. Complete the steps in "Configuring Log File Transfer to a Downstream Capture Database".

2. At the downstream database, set the following initialization parameters to configure archiving of the redo data generated locally:

   • Set at least one archive log destination in the LOG_ARCHIVE_DEST_n initialization parameter either to a directory or to the fast recovery area on the computer system running the downstream database. Set the following attributes of this parameter in the following way:

     • LOCATION - Specify either a valid path name for a disk directory or, to use a fast recovery area, specify USE_DB_RECOVERY_FILE_DEST. This location is the local destination for archived redo log files written from the standby redo logs. Log files from a remote source database should be kept separate from local database log files. See Oracle Database Backup and Recovery User's Guide for information about configuring a fast recovery area.

     • VALID_FOR - Specify either (ONLINE_LOGFILE,PRIMARY_ROLE) or (ONLINE_LOGFILE,ALL_ROLES).

     The following example is a LOG_ARCHIVE_DEST_n setting for the locally generated redo data at the real-time downstream capture database:

     LOG_ARCHIVE_DEST_1='LOCATION=/home/arc_dest/local_rl_dbs2
        VALID_FOR=(ONLINE_LOGFILE,PRIMARY_ROLE)'
     

     A real-time downstream capture configuration should keep archived standby redo log files separate from archived online redo log files generated by the downstream database. Specify ONLINE_LOGFILE instead of ALL_LOGFILES for the redo log type in the VALID_FOR attribute to accomplish this.

     You can specify other attributes in the LOG_ARCHIVE_DEST_n initialization parameter if necessary.

   • Set the LOG_ARCHIVE_DEST_STATE_n initialization parameter that corresponds with the LOG_ARCHIVE_DEST_n parameter previously set in this step to ENABLE.

     For example, if the LOG_ARCHIVE_DEST_1 initialization parameter is set, then set the LOG_ARCHIVE_DEST_STATE_1 parameter in the following way:

     LOG_ARCHIVE_DEST_STATE_1=ENABLE 
     

3. At the downstream database, set the following initialization parameters to configure the downstream database to receive redo data from the source database and write the redo data to the standby redo log at the downstream database:

   • Set at least one archive log destination in the LOG_ARCHIVE_DEST_n initialization parameter either to a directory or to the fast recovery area on the computer system running the downstream database. Set the following attributes of this parameter in the following way:

     • LOCATION - Specify either a valid path name for a disk directory or, to use a fast recovery area, specify USE_DB_RECOVERY_FILE_DEST. This location is the local destination for archived redo log files written from the standby redo logs. Log files from a remote source database should be kept separate from local database log files. See Oracle Database Backup and Recovery User's Guide for information about configuring a fast recovery area.

     • VALID_FOR - Specify either (STANDBY_LOGFILE,PRIMARY_ROLE) or (STANDBY_LOGFILE,ALL_ROLES).

     The following example is a LOG_ARCHIVE_DEST_n setting for the redo data received from the source database at the real-time downstream capture database:

     LOG_ARCHIVE_DEST_2='LOCATION=/home/arc_dest/srl_dbs1
        VALID_FOR=(STANDBY_LOGFILE,PRIMARY_ROLE)'
     

     You can specify other attributes in the LOG_ARCHIVE_DEST_n initialization parameter if necessary.

   • Set the LOG_ARCHIVE_DEST_STATE_n initialization parameter that corresponds with the LOG_ARCHIVE_DEST_n parameter previously set in this step to ENABLE.

     For example, if the LOG_ARCHIVE_DEST_2 initialization parameter is set for the downstream database, then set the LOG_ARCHIVE_DEST_STATE_2 parameter in the following way:

     LOG_ARCHIVE_DEST_STATE_2=ENABLE 
     

   See Also:

   Oracle Database Reference and Oracle Data Guard Concepts and Administration for more information about these initialization parameters

4. If you reset any initialization parameters while an instance was running at a database in Step 2 or 3, then you might want to reset them in the relevant initialization parameter file as well, so that the new values are retained when the database is restarted.

   If you did not reset the initialization parameters while an instance was running, but instead reset them in the initialization parameter file in Step 2 or 3, then restart the database. The source database must be open when it sends redo data to the downstream database, because the global name of the source database is sent to the downstream database only if the source database is open.

5. Create the standby redo log files.

   Note:

   The following steps outline the general procedure for adding standby redo log files to the downstream database. The specific steps and SQL statements used to add standby redo log files depend on your environment. For example, in an Oracle Real Application Clusters (Oracle RAC) environment, the steps are different. See Oracle Data Guard Concepts and Administration for detailed instructions about adding standby redo log files to a database.

   1. In SQL*Plus, connect to the source database dbs1.example.com as an administrative user.

      See Oracle Database Administrator's Guide for information about connecting to a database in SQL*Plus.

   2. Determine the log file size used on the source database. The standby log file size must exactly match (or be larger than) the source database log file size. For example, if the source database log file size is 500 MB, then the standby log file size must be 500 MB or larger. You can determine the size of the redo log files at the source database (in bytes) by querying the V$LOG view at the source database.

      For example, query the V$LOG view:

      SELECT BYTES FROM V$LOG;
      

   3. Determine the number of standby log file groups required on the downstream database. The number of standby log file groups must be at least one more than the number of online log file groups on the source database. For example, if the source database has two online log file groups, then the downstream database must have at least three standby log file groups. You can determine the number of source database online log file groups by querying the V$LOG view at the source database.

      For example, query the V$LOG view:

      SELECT COUNT(GROUP#) FROM V$LOG;
      

   4. In SQL*Plus, connect to the downstream database dbs2.example.com as an administrative user.

   5. Use the SQL statement ALTER DATABASE ADD STANDBY LOGFILE to add the standby log file groups to the downstream database.

      For example, assume that the source database has two online redo log file groups and is using a log file size of 500 MB. In this case, use the following statements to create the appropriate standby log file groups:

      ALTER DATABASE ADD STANDBY LOGFILE GROUP 3
         ('/oracle/dbs/slog3a.rdo', '/oracle/dbs/slog3b.rdo') SIZE 500M;
      
      ALTER DATABASE ADD STANDBY LOGFILE GROUP 4
         ('/oracle/dbs/slog4.rdo', '/oracle/dbs/slog4b.rdo') SIZE 500M;
      
      ALTER DATABASE ADD STANDBY LOGFILE GROUP 5
         ('/oracle/dbs/slog5.rdo', '/oracle/dbs/slog5b.rdo') SIZE 500M;
      

   6. Ensure that the standby log file groups were added successfully by running the following query:

      SELECT GROUP#, THREAD#, SEQUENCE#, ARCHIVED, STATUS
         FROM V$STANDBY_LOG;
      

      You output should be similar to the following:

      GROUP#    THREAD#  SEQUENCE# ARC STATUS
      ---------- ---------- ---------- --- ----------
               3          0          0 YES UNASSIGNED
               4          0          0 YES UNASSIGNED
               5          0          0 YES UNASSIGNED
      

   7. Ensure that log files from the source database are appearing in the location specified in the LOCATION attribute in Step 3. You might need to switch the log file at the source database to see files in the directory.

When these steps are complete, you are ready to configure a real-time downstream capture process. See the instructions in the following sections:

• "Configuring Replication Using the DBMS_STREAMS_ADM Package"

• "Configuring a Real-Time Downstream Capture Process"