Overview of Data Capturing Methods for Oracle Database

Capture Process can extract Oracle database changes either using “LogMiner” functionality or by getting them directly from “Redo” or “Archived Redo” logs (Direct Log Mining).

LogMiner is built-in Oracle method, which is to analyze Redo Logs and extract the databases changes. LogMiner method can be considered in the following cases:

• Small number of changes (less than 5000 DML operations per second) should be replicated
• Possible CPU extra load (up to 15% at peak) is acceptable for the Source Database
• The replication of the LOB columns contain data size more than 4000 bytes is not required
• Size of the changes to be extracted is less than 5% of the Redo log size
• Clustered tables need to be replicated
• Access to Redo/Archived Logs is not possible to configure

In Direct Log Mining mode the Capture Process retrieves Redo Logs and use them to extract the database changes.

Direct Log Mining method best fits for most databases and used to meet the following replications requirements:

• High replication speed
• Minimal impact on the Source Database
• Support LOB columns
• Replication of Clustered Tables is not required
• Replication of Partitioned Index-Organized Tables is not required

Capture Process configuration varies depending on the Redo Log location. It supports Redo Logs located as either on file system or ASM device. Capture Process can also be configured to extract the changes from Redo Log files, which are available in the Repstance instance.

File System Location

For the Redo Logs located on the file system the “ONLINELOG_DIR” and “ARCHIVELOG_DIR” directories should be created (see chapter Prepare Source Database for the details). The “directlogmode” parameter of the Capture Process should be set to “1”.

ASM Device

Capture Process requires ASM connection to be configured to access Redo Logs. The following parameters should be provided:

• asmuser
• asmpassword
• asmservicename

The “directlogmode” parameter should be set to “2”.

Note – The ASM User has to have “sysdba” role assigned.

Repstance Local File System

Capture Process can be configured to extract the changes from Redo Logs delivered into Repstance instance by any external process. This configuration may be used to reduce load to the Oracle Net Services or if the access to Redo Logs through the Oracle Instance is hard to implement. In order to configure the “locallogdir” parameter should be provided and the “directlogmode” parameter should be set to “1”.