About Extract

Extract is a process that is configured to run against the source database or configured to run on a downstream mining database (Oracle only) with capturing data generated in the true source database located somewhere else. This process is the extraction or the data capture mechanism of Oracle GoldenGate.

You can configure an Extract for the following use cases:

• Initial Loads: When you set up Oracle GoldenGate for initial loads, the Extract process captures the current, static set of data directly from the source objects. See Add Initial Load Extract Using the Admin Client and Replicat: Advance Tasks.

• Change Synchronization: When you set up Oracle GoldenGate to keep the source data synchronized with another set of data, the Extract process captures the DML and DDL operations performed on the configured objects after the initial synchronization has taken place. Extracts can run locally on the same server as the database or on another server using the downstream integrated Extract (in case of Oracle database) for reduced overhead. It stores these operations until it receives commit records or rollbacks for the transactions that contain them. If it receives a rollback, it discards the operations for that transaction. If it receives a commit, it persists the transaction to disk in a series of files called a trail, where it is queued for propagation to the target system. All the operations in each transaction are written to the trail as a sequentially organized transaction unit and are in the order in which they were committed to the database (commit sequence order). This design ensures both speed and data integrity.

Note:

Extract ignores operations on objects that are not in the Extract configuration, even though a transaction may also include operations on objects that are in the Extract configuration.

The Extract process can be configured to capture data from the following types of data sources:

• Source tables: This source type is used for initial loads.

• Database recovery logs or transaction logs: While capturing from the logs, the actual method varies depending on the database type. An example of this source type is the Oracle database redo logs, which are used for supplemental logging.