Understand the Oracle Golden Gate and its components

Understand the Oracle GoldenGate Flow:
1. captured from the source database. The captured data is written to a file called the source trail
2. trail is then read by a datapump, sent across the network, and written to a remote trail file by the Collector process
3. The delivery function reads the remote trail and updates the target database
4. Each of the components is managed by the Manager process

Note: DATAPUMP and COLLECTOR process are optional process.

GoldenGate Components:

1. Source Database
Following is the list of Source database which golden gate support:
DB2 for Linux, UNIX, Windows
DB2 for z/OS
SQL Server

2. Capture (Local Extract) Process
Capture is the process of extracting data that is inserted into, updated on, or deleted from the source database.
In GoldenGate, the capture process is called the Extract. In this case, the Extract is called a Local Extract (sometimes called the Primary Extract) because it captures data changes from the local source database.
Extract is an operating-system process that runs on the source server and captures changes from the database transaction logs.
Extract captures changes from the redologs (and in some exceptional cases, the archived redo logs) and writes the data to a file called the Trail File. For Microsoft SQL Server, Extract captures changes from the transaction log. To reduce the amount of processing, Extract only captures committed changes and filters out other activity such as rolled-back changes.

3. Source Trail
The Extract process sequentially writes committed transactions as they occur to a staging file that GoldenGate calls a source trail. Data is written in large blocks for high performance. Data that is written to the trail is queued for distribution to the target server or another destination to be processed by another GoldenGate process, such as a data pump

Note GoldenGate uses a Commit Sequence Number (CSN) to identify and keep track of transactions processed by GoldenGate and to ensure data integrity. The CSN is a GoldenGate platform-independent representation of unique serial numbers that each DBMS uses to track the transactions it has processed. For example, in an Oracle database, GoldenGate uses the Oracle System Change Number (SCN) to represent the CSN. For a SQL Server database, GoldenGate uses a concatenation of the virtual log-file number, a segment number within the virtual log, and the entry number. Extract writes the CSNs to the checkpoint and trail files that you can view using the Logdump utility. You can use the CSN when starting the Replicat to begin processing at or after a specific CSN.

4. Data Pump
The data pump is another type of GoldenGate Extract process. The data pump reads the records in the source trail written by the Local Extract, pumps or passes them over the TCP/IP network to the target, and creates a target or remote trail.

5. Collector
The Collector process is started automatically by the Manager as needed by the Extract. The Collector process runs in the background on the target system and writes records to the remote trail.

6. Remote Trail
The remote trail is similar to the source trail, except it is created on the remote server, which could be the target database server or some other middle tier server. The source trails and the remote trails are stored in a filesystem directory named dirdat by default.

7. Delivery (Replicat)
Delivery is the process of applying data changes to the target database. In GoldenGate, delivery is done by a process called the Replicat using the native database SQL. The Replicat applies data changes written to the trail file by the Extract process in the same order in which they were committed on the source database.

8. Target Database:
Same as source

9. Manager
The GoldenGate Manager process is used to manage all of the GoldenGate processes and resources. A single Manager process runs on each server where GoldenGate is executing and processes commands from the GoldenGate Software Command Interface (GGSCI). The Manager process is the first GoldenGate process started. The Manager then starts and stops each of the other GoldenGate processes, manages the trail files, and produces log files and reports.


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