The Integrated Capture GoldenGate Mode also known as the Integrated Extract Goldengate process in 12c (also backported to 11gr2) is one of the more interesting and useful feature released with this version. This capture process is the component responsible for extracting the DML transactional data and DDL’s from the source database redo log files. This data is then written to local trail files which eventually is move to the destination database to be applied there.
Here are the list of topics to be covered in this article.
• What is the GoldenGate Integrated Capture Mode?
• Integrated Extract Goldengate vs Classic Capture
• On-Source Capture
• Downstream Capture
What is the GoldenGate Integrated Capture Mode?
Integrated Capture Mode (IC) is a new form of the Extract process, were in this process is moved closer, inside the source database. In the traditional Classic extract process, the extract works on the redo logs outside the domain of the actual database. In this new integrated capture mode, a server Log Miner process is started which extracts all the DML data and DDLS statements creating Logical Change Records (LCR’s). These are then handed to the Goldengate memory processes which writes these LCR’s to the local trail files. This Log Miner server process is not the Log Miner utility we are used to in the database but is a similar mechanism which has been tuned and enhanced for specific use by the Goldengate processes.
The purpose of moving this inside the database is to be able to make use of the already existing internal procedures in the database, making it easier to provide support for the newer features of Oracle faster than was previously possible. Due to this change, Oracle is now able to provide the following.
• Full Support of Basic, OLTP and EHCC compressed data.
• No need to fetch LOB’s from tables.
• Full Secure File support for Secure file lobs.
• Full XML support.
• Automatically handles addition of nodes and threads in RAC environment.
• Senses node up down in RAC and handles it in its processes transparently.
Integrated Capture vs Classic Capture
The Integrated Capture mode offers the following.
• Integrated with Database features
• Allows to mine earlier versions of integrated capture on secondary
• More efficient. It does not have to fetch data because of the datatype, etc..
• No longer necessary to set this: Threads, ASMUSER, ASMBUF, DBLOGREADER, DECRYPASSWORD
• For RAC no additional manual steps required. Transparent with RAC.
Integrated Capture Modes
Integration capture supports two types of deployment configurations. They are:
• On-Source Capture
• Downstream Capture
When the integrated capture process is configured using the on-source capture mode, the capture process is started on the actual source database server itself. Changes as they happen on source database will be captured locally, routed, transformed and applied on target database in near real-time.
This may seem convenient but consideration needs to be given to the additional workload that will be placed by this process on the database server. However if real-time replication is required this is the best option.
Note: All features are supported in both On-Source or Downstream Deployment
In the downstream mode, the capture process is configured to run on a remote database host. All the database redo logs from the source database are shipped to this remote server using Dataguard technology and then mined there by the capture process.
In this mode there is an inherent latency introduced due to the fact that the redo log on the source needs to switch first before the log can be shipped downstream. So there will be some delay in the replication of data to a target database as the extraction will be delayed due to the log switch. The main benefit of this setup however is the offset of the resource usage on the source server.
In this mode, to overcome the log switch latency, Oracle has provide a near Real time capture using Standby redo logs for extraction. In this configuration the redo log from the source continuously writes into the standby redo logs of the downstream database. The capture process directly capture the data from here.
It is important to keep in mind when deciding whether to use the Integrated capture or the classic capture mechanism that both configuration will remain available in future releases. However Oracle recommends to use the new Integrated capture mechanism as Oracle will not be adding new features to classic capture in the future and it will only be there for legacy support purposes.
The database where integrated capture runs:
• Must be at least 11.2.0..3
• Database patch 1411356.1 must be installed.
• Works with Oracle 12c.