START EXTRACT

Use START EXTRACT to start the Extract process. To confirm that Extract has started, use the INFO EXTRACT or STATUS EXTRACT command. Extract can be started at its normal start point (from initial or current checkpoints) or from an alternate, user-specified position in the data source.

Normal Start Point

Without options, START EXTRACT directs a primary Extract and a data pump Extract to start processing at one of the following locations in the data source to maintain data integrity:

  • After graceful or abnormal termination: At the first unprocessed transaction in the data source from the previous run, as represented by the current read checkpoint.

  • First-time startup after the group was created: At the start point specified with the ADD EXTRACT command.

See Administering Oracle GoldenGate for Windows and UNIX for more information about checkpoints.

Extract also can be started from the command line of the operating system for certain synchronization configurations. For more information on the proper configuration and startup method to use for your purposes, see Administering Oracle GoldenGate for Windows and UNIX.

Alternate Start Point

The ATCSN and AFTERCSN options enable you to establish a logical starting point for a primary Extract or a data pump, after you establish an approximate physical starting point with the ADD EXTRACT or ALTER EXTRACT command. For example, in an initial-load scenario, after a backup is applied to the target, the serial identifier of the last transaction (such as an Oracle SCN) can be mapped to an Oracle GoldenGate CSN (commit sequence number) value, which can be used to start Extract with the AFTERCSN option. By starting with the first transaction after the specified CSN, Extract omits the transactions that were included in the backup, which would otherwise cause duplicate-record and missing-record errors.

Before starting Extract with ATCSN or AFTERCSN, you must establish a physical starting location with one of the following commands:

  • ADD EXTRACT with the BEGIN option set to a timestamp that is earlier than the CSN value specified with ATCSN or AFTERCSN. The transaction log that contains the timestamp and every log thereafter must be available on the system before Extract is started.

  • ALTER EXTRACT to the sequence number of the log that contains the CSN specified with ATCSN or AFTERCSN.

Note:

See Administering Oracle GoldenGate for Windows and UNIX for more information about the values that comprise a CSN for a given database.

Syntax

START EXTRACT group_name [ATCSN csn | AFTERCSN csn]
group_name

The name of an Extract group or a wildcard (*) to specify multiple groups. For example, T* starts all Extract groups whose names begin with T.

ATCSN csn | AFTERCSN csn

Specifies an alternate start point. (See "Alternate Start Point" for usage instructions.)

ATCSN

Directs Extract to position its start point at the first transaction that has the specified CSN. Any transactions in the data source that have CSN values less than the specified one are skipped.

AFTERCSN

Directs Extract to position its start point at the beginning of the first transaction after the one that has the specified CSN. Any transactions in the data source that have CSN values that are less than, or equal to, the specified one are skipped.

csn

Specifies a CSN value. Enter the CSN value in the format that is valid for the database. See Administering Oracle GoldenGate for Windows and UNIX for CSN formats and descriptions. Extract abends if the format is invalid and writes a message to the report file. To determine the CSN to supply after an initial load is complete, use the serial identifier at which the load utility completed. Otherwise, follow the instructions in the initial load procedure for determining when to start Extract.

The following are additional guidelines to observe when using ATCSN and AFTERCSN:

  • To support starting at, or after, a CSN, the trail must be of Oracle GoldenGate version 10.0.0 or later, because the CSN is stored in the file header so that it is available to downstream processes.

  • When a record that is specified with a CSN is found, Extract issues a checkpoint. The checkpoint ensures that subsequent Extract startups begin from the requested location, and not from a point prior to the requested CSN.

  • You must establish a physical start point in the transaction log or trail for Extract with ADD EXTRACT or ALTER EXTRACT before using ATCSN or AFTERCSN. These options are intended to be an additional filter after Extract is positioned to a physical location in the data source.

Examples

Example 1   
START EXTRACT finance
Example 2   
START EXTRACT finance ATCSN 684993
Example 3   
START EXTRACT finance AFTERCSN 684993