Extract Process : 

Extract process captures all the changes made to all objects which we configure for Golden Gate for the synchronization process. It reads data either from transaction logs of database or archive log files.

Once those transactions are completed, the Extract process sends all details of those transactions to trail files for propagation to the target system.

We can configure two types of Extract Process :

  1. Primary Extract Process: Primary Extract process can read data directly from the source table for the initial load process. It captures changed data from database logs or archive logs. It can then send data to local trail files or remote trail files.
  2. Secondary or Data Pump Extract Process: It is an optional process but a highly recommended process. It is used to distribute data from local trail files to a remote server.

Setting Change Capture:

Extract process is added on Source System.

Steps to configure Change Capture using Primary Extract

1. Add Primary Extract, This process has an associated parameter file and it reads from the transaction logs located at source system.

Login to ggsci :

GGSCI (localhost.localdomain) 1> dblogin userid ggs_owner@orcl
Successfully logged into database.

Add Extract

GGSCI (localhost.localdomain as ggs_owner@orcl)2> add extract ext2 , tranlog , begin now
EXTRACT added.

Check with info all command that extract is added

GGSCI (localhost.localdomain as ggs_owner@orcl) 3> info all  

Program     Status      Group       Lag at Chkpt  Time Since Chkpt

MANAGER     RUNNING                                           
EXTRACT     STOPPED     EXT1        00:00:00      384:28:54       
EXTRACT     STOPPED     EXT2        00:00:00      00:00:20

2. Edit Parameter File

GGSCI (localhost.localdomain as ggs_owner@orcl) 4> edit params ext2
Extract ext2
exttrail /u02/ggate/dirdat/ab
userid ggs_owner@orcl, password oracle
Table hr.*;

3. Add exttrail/rmttrail for extract ext2

GGSCI (localhost.localdomain as ggs_owner@orcl) 12> add exttrail /u02/ggate/dirdat/ab, EXTRACT EXT2

4. Start Extract Process

GGSCI (localhost.localdomain as ggs_owner@orcl) 13> start extract ext2

Sending START request to MANAGER ...
EXTRACT EXT2 starting

5. Check extract process is running using info all command unless you find info command you will not get extract process status.

GGSCI (localhost.localdomain as ggs_owner@orcl) 14> info all

Program     Status      Group       Lag at Chkpt  Time Since Chkpt

MANAGER     RUNNING                                           
EXTRACT     STOPPED     EXT1        00:00:00      386:32:52   
EXTRACT     RUNNING     EXT2        00:00:00      00:00:00    

Steps to Configure Change Capture with Secondary Capture : 

Data Pump is called secondary extract in Oracle Golden Gate environment.

A data pump extract can write to one or many remote trails and servers.

The task of Data Pump Extract :

1. Reads local trail files.

2. Manipulate data or passes it without any change.

3. Sends those data to one or many targets.

It is optional but highly recommended as it provides many benefits as below :

1. Data Pump extract is useful as a safeguard against network or target failures means when we use only primary extract and use the remote trail for capture and replication when the network goes down or target server goes down trail files may fail or lose. But when we use data pump extract it ensures that the trail file is at least stored locally.

2. Data Pump Extract is useful to break complex data filtering and transformation into phases.

3. Use Data Pump Extract we can consolidate data from many sources.

4. We can use Data Pump Extract to synchronize one source with multiple targets.

Let us add one Data Pump Extract for primary extract we have created in the previous example :

Step 1: Add extract with exttrailsource as primary extract trail files.

GGSCI (localhost.localdomain as ggs_owner@orcl) 15> add extract pump2 , exttrailsource /u02/ggate/dirdat/ab
EXTRACT added.

Step 2: Check extract added with info all command

GGSCI (localhost.localdomain as ggs_owner@orcl) 14> info all

Program     Status      Group       Lag at Chkpt  Time Since Chkpt

MANAGER     RUNNING                                           
EXTRACT     STOPPED     EXT1        00:00:00      399:16:01   
EXTRACT     RUNNING     EXT2        00:00:00      00:00:08    
EXTRACT     STOPPED     EXT_HR      00:00:00      15:02:28    
EXTRACT     STOPPED     EXT_HR1     00:00:00      13:56:31    
EXTRACT     STOPPED     PUMP2       00:00:00      00:00:03

Step 3: Configure parameter of pump2 [secondary ] extract

GGSCI (localhost.localdomain as ggs_owner@orcl) 16> edit params pump2

I have set the following parameters for pump2 extract

extract pump2
rmthost repserver,mgrport 7809
rmttrail ./dirdat/ba
table hr.*;

I have set remote host with replication server and remote trail [rmttrail] as ./dirdat/ba.

This process will copy local trail file to remote destination: repserver at a defined location in rmttrail.

Step 4: add a rmttrail option with a pump2 extract from ggsci prompt.

GGSCI (localhost.localdomain as ggs_owner@orcl) 20> add rmttrail ./dirdat/ba , extract pump2

Step 5: Start pump2 extract

GGSCI (localhost.localdomain as ggs_owner@orcl) 21> start extract pump2    

Sending START request to MANAGER ...
EXTRACT PUMP2 starting

Step 6: Check pump2 process is running

GGSCI (localhost.localdomain as ggs_owner@orcl) 22> info all

Program     Status      Group       Lag at Chkpt  Time Since Chkpt

MANAGER     RUNNING                                           
EXTRACT     STOPPED     EXT1        00:00:00      399:21:39   
EXTRACT     RUNNING     EXT2        00:00:00      00:00:06    
EXTRACT     STOPPED     EXT_HR      00:00:00      15:08:06    
EXTRACT     STOPPED     EXT_HR1     00:00:00      14:02:09    
EXTRACT     RUNNING     PUMP2       00:00:00      00:00:05    

In the next article, we will see configuring change delivery.

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