Positions within the Oracle replication processe can be identified and/or set using the Oracle System Change Number (SCN) reference. By setting the replication to start at a specific SCN you can take advantage of provisioning, or starting replication on specific known boundaries, for example, after a specific backup operation, or snapshot, has taken place.
By default tpm sets up Oracle replication to start at
the current position of the Oracle DBMS, which is denoted by the current
SCN. The replicator represents this value using the word
NOW. To enable default behavior
simply install normally and include the tpm
--start-and-report option in the
installation. The replicator will extract the first transaction committed
after the time when the replicator was installed.
To start replication at a specific SCN in the past, you must bring the replicator online explicitly with an option that specifies the exact SCN where replication should start. Here are the exact steps.
Determine the SCN from which you would like to begin replication.
After installation completes successfully, start the replicator on the source Oracle instance and bring it online using the following commands:
replicator start offlineshell>
trepctl online -from-event
Start the target replicator(s) normally using:
Replication will now start at the target SCN value. Here is a short example of how to select the target SCN and then bring the replicator online to pick up older changes.
select current_scn from v$database;CURRENT_SCN ----------- 14140241
Depending on how old the SCN is the replicator may take a while to extract up to the current position of the Oracle instance. You can confirm that older data were extracted by looking in the log using the thl utility.
It is important to note that specifying an older SCN will require the source host to still have, on disk, all the Archive Logs up to and including that position. If you have RMAN or some other process periodically backing up and removing Archive Logs, you will need to restore them first.
You can reset replicators to begin extracting from a specific SCN after replication has been installed using the following procedure:
Reset target and source replicators using the reset command to clear all logs:
trepctl -service servicename reset -all -y
Bring the source replicator online starting at the desired SCN:
trepctl -service servicename online -from-event 14140241
Bring the target replicator online normally:
trepctl -service servicename online
You can use the
command to change the position of replication in the source Oracle
instance. This allows you to skip over parts of the log or reposition
replication without disturbing target replicators.
Bring the source replicator offline and reset the redo component only.
trepctl -service servicename offlineshell>
trepctl -service servicename reset -redo -y
Bring the source replicator online starting at the desired SCN.
trepctl -service servicename online -from-event 61754320
Target replicators will automatically reconnect to the source replicator.