|Oracle® Streams Replication Administrator's Guide
11g Release 2 (11.2)
|PDF · Mobi · ePub|
This chapter contains these topics:
Note:A new feature called XStream is available in Oracle Database 11g Release 2 (11.2) and later. XStream enables Oracle Call Interface and Java applications to access the database changes in a stream. See Oracle Database XStream Guide for information about XStream.
To share DML changes from an Oracle source database to a non-Oracle destination database, the Oracle database functions as a proxy and carries out some steps that would usually be done at the destination database. That is, the LCRs intended for the non-Oracle destination database are dequeued in the Oracle database itself and an apply process at the Oracle database applies the changes to the non-Oracle database across a network connection through an Oracle Database Gateway. Figure 11-1 shows an Oracle database sharing data with a non-Oracle database.
You should configure the Oracle Database Gateway to use the transaction model
See Also:The Oracle documentation for your specific Oracle Database Gateway for information about using the transaction model
COMMIT_CONFIRMfor your Oracle Database Gateway
In an Oracle to non-Oracle environment, a capture process or a synchronous capture functions the same way as it would in an Oracle-only environment. That is, a capture process finds changes in the redo log, captures them based on its rules, and enqueues the captured changes as logical change records (LCRs) into an
ANYDATA queue. A synchronous capture uses an internal mechanism to capture changes based on its rules and enqueue the captured changes as row LCRs into an
ANYDATA queue. In addition, a single capture process or synchronous capture can capture changes that will be applied at both Oracle and non-Oracle databases.
ANYDATA queue that stages the LCRs functions the same way as it would in an Oracle-only environment, and you can propagate LCRs to any number of intermediate queues in Oracle databases before they are applied at a non-Oracle database.
Oracle Streams Concepts and Administration for general information about capture processes, synchronous captures, staging, and propagations
Chapter 1, "Preparing for Oracle Streams Replication" for information about capture processes, synchronous captures, staging, and propagations in an Oracle Streams replication environment
An apply process running in an Oracle database uses Heterogeneous Services and an Oracle Database Gateway to apply changes encapsulated in LCRs directly to database objects in a non-Oracle database. The LCRs are not propagated to a queue in the non-Oracle database, as they would be in an Oracle-only Oracle Streams environment. Instead, the apply process applies the changes directly through a database link to the non-Oracle database.
Note:Oracle Streams apply processes do not support Generic Connectivity.
This section describes the configuration of an apply process that will apply changes to a non-Oracle database.
Before you create an apply process that will apply changes to a non-Oracle database, configure Heterogeneous Services, the Oracle Database Gateway, and a database link.
Oracle Streams supports the following Oracle Database Gateways:
Oracle Database Gateway for Sybase
Oracle Database Gateway for Informix
Oracle Database Gateway for SQL Server
Oracle Database Gateway for DRDA
The database link will be used by the apply process to apply the changes to the non-Oracle database. The database link must be created with an explicit
Oracle Database Heterogeneous Connectivity User's Guide for more information about Heterogeneous Services and Oracle Database Gateway
The Oracle documentation for your Oracle Database Gateway
After the database link has been created and is working properly, create the apply process using the
CREATE_APPLY procedure in the
DBMS_APPLY_ADM package and specify the database link for the
apply_database_link parameter. After you create an apply process, you can use apply process rules to specify which changes are applied at the non-Oracle database.
Oracle Database PL/SQL Packages and Types Reference for more information about the procedures in the
Oracle Streams Concepts and Administration for information about specifying apply process rules
If you use substitute key columns for any of the tables at the non-Oracle database, then specify the database link to the non-Oracle database when you run the
SET_KEY_COLUMNS procedure in the
You must set the
parallelism apply process parameter to
1, the default setting, when an apply process is applying changes to a non-Oracle database. Currently, parallel apply to non-Oracle databases is not supported. However, you can use multiple apply processes to apply changes a non-Oracle database.
If you use a procedure DML handler to process row LCRs for any of the tables at the non-Oracle database, then specify the database link to the non-Oracle database when you run the
SET_DML_HANDLER procedure in the
See Also:Oracle Streams Concepts and Administration for information about message processing options for an apply process
If you want to use a message handler to process user messages for a non-Oracle database, then, when you run the
CREATE_APPLY procedure in the
DBMS_APPLY_ADM package, specify the database link to the non-Oracle database using the
apply_database_link parameter, and specify the message handler procedure using the
Currently, error handlers and conflict handlers are not supported when sharing data from an Oracle database to a non-Oracle database. If an apply error occurs, then the transaction containing the LCR that caused the error is moved into the error queue in the Oracle database.
When applying changes to a non-Oracle database, an apply process applies changes made to columns of only the following data types:
The apply process does not apply changes in columns of the following data types to non-Oracle databases:
UROWID, user-defined types (including object types,
REFs, varrays, and nested tables), and Oracle-supplied types (including
Any types, XML types, spatial types, and media types). The apply process raises an error when an LCR contains a data type that is not listed, and the transaction containing the LCR that caused the error is moved to the error queue in the Oracle database.
Each Oracle Database Gateway might have further limitations regarding data types. For a data type to be supported in an Oracle to non-Oracle environment, the data type must be supported by both Oracle Streams and the Oracle Database Gateway being used.
Oracle Database SQL Language Reference for more information about these data types
The Oracle documentation for your specific Oracle Database Gateway
When you specify that DML changes made to certain tables should be applied at a non-Oracle database, an apply process can apply only the following types of DML changes:
Note:The apply process cannot apply DDL changes at non-Oracle databases.
Before you start an apply process that applies changes to a non-Oracle database, complete the following steps to instantiate each table at the non-Oracle database:
DBMS_HS_PASSTHROUGH package or the tools supplied with the non-Oracle database to create the table at the non-Oracle database.
The following is an example that uses the
DBMS_HS_PASSTHROUGH package to create the
hr.regions table in the
het.example.com non-Oracle database:
DECLARE ret INTEGER; BEGIN ret := DBMS_HS_PASSTHROUGH.EXECUTE_IMMEDIATE@het.example.com ( 'CREATE TABLE regions (region_id INTEGER, region_name VARCHAR(50))'); END; / COMMIT;
See Also:Oracle Database Heterogeneous Connectivity User's Guide and the Oracle documentation for your specific Oracle Database Gateway for more information about Heterogeneous Services and Oracle Database Gateway
If the changes that will be shared between the Oracle and non-Oracle database are captured by a capture process or synchronous capture at the Oracle database, then prepare all tables that will share data for instantiation.
Create a PL/SQL procedure (or a C program) that performs the following actions:
Gets the current SCN using the
GET_SYSTEM_CHANGE_NUMBER function in the
ENABLE_AT_SYSTEM_CHANGE_NUMBER procedure in the
DBMS_FLASHBACK package to set the current session to the obtained SCN. This action ensures that all fetches are done using the same SCN.
Populates the table at the non-Oracle site by fetching row by row from the table at the Oracle database and then inserting row by row into the table at the non-Oracle database. All fetches should be done at the SCN obtained using the
For example, the following PL/SQL procedure gets the flashback SCN, fetches each row in the
hr.regions table in the current Oracle database, and inserts them into the
hr.regions table in the
het.example.com non-Oracle database. Notice that flashback is disabled before the rows are inserted into the non-Oracle database.
SET SERVEROUTPUT ON CREATE OR REPLACE PROCEDURE insert_reg IS CURSOR c1 IS SELECT region_id, region_name FROM hr.regions; c1_rec c1 % ROWTYPE; scn NUMBER; BEGIN scn := DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER(); DBMS_FLASHBACK.ENABLE_AT_SYSTEM_CHANGE_NUMBER( query_scn => scn); /* Open c1 in flashback mode */ OPEN c1; /* Disable Flashback */ DBMS_FLASHBACK.DISABLE; LOOP FETCH c1 INTO c1_rec; EXIT WHEN c1%NOTFOUND; /* Note that all the DML operations inside the loop are performed with Flashback disabled */ INSERT INTO email@example.com VALUES ( c1_rec.region_id, c1_rec.region_name); END LOOP; COMMIT; DBMS_OUTPUT.PUT_LINE('SCN = ' || scn); EXCEPTION WHEN OTHERS THEN DBMS_FLASHBACK.DISABLE; RAISE; END; /
Make a note of the SCN returned.
If the Oracle Database Gateway you are using supports the Heterogeneous Services callback functionality, then you can replace the loop in the previous example with the following SQL statement:
INSERT INTO firstname.lastname@example.org SELECT * FROM hr.region@!;
Note:The user who creates and runs the procedure in the previous example must have
EXECUTEprivilege on the
DBMS_FLASHBACKpackage and all privileges on the tables involved.
See Also:Oracle Database Heterogeneous Connectivity User's Guide and the Oracle documentation for your specific Oracle Database Gateway for information about callback functionality and your Oracle Database Gateway
Set the instantiation SCN for the table at the non-Oracle database. Specify the SCN you obtained in Step 3 in the
SET_TABLE_INSTANTIATION_SCN procedure in the
DBMS_APPLY_ADM package to instruct the apply process to skip all LCRs with changes that occurred before the SCN you obtained in Step 3. Ensure that you set the
apply_database_link parameter to the database link for the remote non-Oracle database.
See Also:"Setting Instantiation SCNs at a Destination Database" and Oracle Database PL/SQL Packages and Types Reference for more information about the
In an Oracle to non-Oracle environment, you can specify rule-based transformations during capture or apply the same way as you would in an Oracle-only environment. In addition, if your environment propagates LCRs to one or more intermediate Oracle databases before they are applied at a non-Oracle database, then you can specify a rule-based transformation during propagation from a queue at an Oracle database to another queue at an Oracle database.
See Also:Oracle Streams Concepts and Administration for more information about rule-based transformations
Messaging Gateway is a feature of the Oracle database that provides propagation between Oracle queues and non-Oracle message queuing systems. Messages enqueued into an Oracle queue are automatically propagated to a non-Oracle queue, and the messages enqueued into a non-Oracle queue are automatically propagated to an Oracle queue. It provides guaranteed message delivery to the non-Oracle messaging system and supports the native message format for the non-Oracle messaging system. It also supports specification of user-defined transformations that are invoked while propagating from an Oracle queue to the non-Oracle messaging system or from the non-Oracle messaging system to an Oracle queue.
See Also:Oracle Streams Advanced Queuing User's Guide for more information about the Messaging Gateway
If the apply process encounters an unhandled error when it tries to apply an LCR at a non-Oracle database, then the transaction containing the LCR is placed in the error queue in the Oracle database that is running the apply process. The apply process detects data conflicts in the same way as it does in an Oracle-only environment, but automatic conflict resolution is not supported currently in an Oracle to non-Oracle environment. Therefore, any data conflicts encountered are treated as apply errors.
Oracle Streams Extended Examples contains a detailed example that includes sharing data in an Oracle to non-Oracle Streams environment.
To capture and propagate changes from a non-Oracle database to an Oracle database, a custom application is required. This application gets the changes made to the non-Oracle database by reading from transaction logs, by using triggers, or by some other method. The application must assemble and order the transactions and must convert each change into a logical change record (LCR). Next, the application must enqueue the LCRs in an Oracle database using the
DBMS_STREAMS_MESSAGING package or the
DBMS_AQ package. The application must commit after enqueuing all LCRs in each transaction. Figure 11-2 shows a non-Oracle databases sharing data with an Oracle database.
Because the custom user application is responsible for assembling changes at the non-Oracle database into LCRs and enqueuing the LCRs at the Oracle database, the application is completely responsible for change capture. Therefore, the application must construct LCRs that represent changes at the non-Oracle database and then enqueue these LCRs into the queue at the Oracle database. The application can enqueue multiple transactions concurrently, but the transactions must be committed in the same order as the transactions on the non-Oracle source database.
See Also:"Constructing and Enqueuing LCRs" for more information about constructing and enqueuing LCRs
To ensure the same transactional consistency at both the Oracle database where changes are applied and the non-Oracle database where changes originate, you must use a transactional queue to stage the LCRs at the Oracle database. For example, suppose a single transaction contains three row changes, and the custom application enqueues three row LCRs, one for each change, and then commits. With a transactional queue, a commit is performed by the apply process after the third row LCR, retaining the consistency of the transaction. If you use a nontransactional queue, then a commit is performed for each row LCR by the apply process. The
SET_UP_QUEUE procedure in the
DBMS_STREAMS_ADM package creates a transactional queue automatically.
Also, the queue at the Oracle database should be a commit-time queue. A commit-time queue orders LCRs by approximate commit system change number (approximate CSCN) of the transaction that includes the LCRs. Commit-time queues preserve transactional dependency ordering between LCRs in the queue, if the application that enqueued the LCRs commits the transactions in the correct order. Also, commit-time queues ensure consistent browses of LCRs in a queue.
In a non-Oracle to Oracle environment, the apply process functions the same way as it would in an Oracle-only environment. That is, it dequeues each LCR from its associated queue based on apply process rules, performs any rule-based transformation, and either sends the LCR to a handler or applies it directly. Error handling and conflict resolution also function the same as they would in an Oracle-only environment. So, you can specify a prebuilt update conflict handler or create a custom conflict handler to resolve conflicts.
The apply process should be configured to apply persistent LCRs, not captured LCRs. So, the apply process should be created using the
CREATE_APPLY procedure in the
DBMS_APPLY_ADM package, and the
apply_captured parameter should be set to
FALSE when you run this procedure. After the apply process is created, you can use procedures in the
DBMS_STREAMS_ADM package to add rules for LCRs to the apply process rule sets.
There is no automatic way to instantiate tables that exist at a non-Oracle database at an Oracle database. However, you can perform the following general procedure to instantiate a table manually:
At the non-Oracle database, use a non-Oracle utility to export the table to a flat file.
At the Oracle database, create an empty table that matches the table at the non-Oracle database.
At the Oracle database, use SQL*Loader to load the contents of the flat file into the table.
See Also:Oracle Database Utilities for information about using SQL*Loader
Oracle Streams supports data sharing between two non-Oracle databases through a combination of non-Oracle to Oracle data sharing and Oracle to non-Oracle data sharing. Such an environment would use Oracle Streams in an Oracle database as an intermediate database between two non-Oracle databases.
For example, a non-Oracle to non-Oracle environment can consist of the following databases:
A non-Oracle database named
An Oracle database named
A non-Oracle database named
A user application assembles changes at
het1.example.com and enqueues them in
dbs1.example.com. Next, the apply process at
dbs1.example.com applies the changes to
het2.example.com using Heterogeneous Services and an Oracle Database Gateway. Another apply process at
dbs1.example.com could apply some or all of the changes in the queue locally at
dbs1.example.com. One or more propagations at
dbs1.example.com could propagate some or all of the changes in the queue to other Oracle databases.