Operation logs for databases

Most changes to a replicated database are recorded as entries in an operation log (oplog). These entries store all the information required to replay the changes in another replica.

The information included in the oplog is as follows:
  • The identity of the replica in which the change originated.
  • The specific changes to a database record or to a schema in the schema repository made during a single checkout; for example, submission of a new record, schema updates, and so on.
  • An integer sequence number: 1 for the first change originating at a particular replica, 2 for the next change, and so on. This is called the oplog ID of the oplog entry.

The exact kind and amount of information varies with the specific operation. For example, an oplog entry for the submission of a new record has different, and more, information than an oplog entry for modifying an existing record.

Note: You can delete a replica’s oplog entries after they have been used to update other replicas.

You do not need the following topics to use MultiSite, but it is helpful when you want to deepen your understanding of the error-recovery facilities.