Oracle Consulting Oracle Training Oracle Support Development
Home
Catalog
Oracle Books
SQL Server Books
IT Books
Job Interview Books
eBooks
Rampant Horse Books
911 Series
Pedagogue Books

Oracle Software
image
Write for Rampant
Publish with Rampant
Rampant News
Rampant Authors
Rampant Staff
 Phone
 800-766-1884
Oracle News
Oracle Forum
Oracle Tips
Articles by our Authors
Press Releases
SQL Server Books
image
image

Oracle 11g Books

Oracle tuning

Oracle training

Oracle support

Remote Oracle

STATSPACK Viewer

Privacy Policy

 

   
 

Streams log miner dictionary

Oracle Tips by Burleson 

Oracle Streams
Capture and Propagate Configuration

LogMiner Data Dictionary

The Capture process makes use of a data dictionary, which is different from the source database data dictionary. This special data dictionary is called the LogMiner Data Dictionary. The Capture process requires a LogMiner data dictionary because the information in the primary data dictionary may not match the changes being captured from the redo log. These changes may have occurred minutes, hours, or even days before they are captured by a Capture process. This is important in the sense that when the actual capture takes place, it needs to have the right dictionary information. Since the timing of the Capture process and timing of the actual database table change can be different, the maintenance of the log dictionary, which can provide time sensitive dictionary information, becomes significant.

The first time a Capture process is started at the database, Oracle uses the extracted data dictionary information in the redo log to create a LogMiner data dictionary.  This dictionary is separate from the primary data dictionary for the source database. Additional Capture processes may use this existing LogMiner data dictionary, or they may create new LogMiner data dictionaries.

Since the Capture process can have its own timing, when it does extract and create the LCRs, the object’s structure in the primary dictionary may not match. The Capture process cannot depend on the primary data dictionary, especially when it is stopped for some time. This is the reason that the LogMiner Data Dictionary is maintained.

 

LogMiner Data Dictionary

The dbms_capture_adm.build procedure extracts data dictionary information to the redo log. The extracted data dictionary information in the redo log is consistent with the primary data dictionary at the time when the dbms_capture_adm.build procedure is run. The build procedure is automatically run when the Capture process is created.

The amount of information extracted to a redo log, when the dbms_capture_adm.build procedure is run, depends on the number of database objects in the database. The dbms_capture_adm.build procedure generates a corresponding valid first SCN value that can be specified when the new Capture process is created. A First SCN generated by the dbms_capture_adm.build procedure can be found by running the following query:

SELECT DISTINCT FIRST_CHANGE#, NAME FROM V$ARCHIVED_LOG WHERE DICTIONARY_BEGIN = 'YES';

Propagation and Apply processes use a Streams data dictionary to keep track of the database objects from a particular source database. A Streams data dictionary is populated whenever one or more database objects are prepared for instantiation at a source database. When a database object is prepared for instantiation, it is recorded in the redo log. When a Capture process scans the redo log, it uses this information to populate the local Streams data dictionary for the source database. After an object has been prepared for instantiation, the local Streams data dictionary is updated whenever a DDL statement on the object is processed by a Capture Process.


The above text is an excerpt from:

Oracle Streams
High Speed Replication and Data Sharing

ISBN 0-9745993-5-2

by Madhu Tumma
 


Download your Oracle scripts now:

www.oracle-script.com

The definitive Oracle Script collection for every Oracle professional DBA

Linux Oracle commands syntax poster

ION Oracle tuning software

Oracle data dictionary reference poster



Oracle Forum

BC Oracle consulting support training

BC remote Oracle DBA   

 

   

 Copyright © 1996 -2016 by Burleson. All rights reserved.


Oracle® is the registered trademark of Oracle Corporation. SQL Server® is the registered trademark of Microsoft Corporation. 
Many of the designations used by computer vendors to distinguish their products are claimed as Trademarks