A replication is a copy of a database which can be used for recovery or as a shadow database.
Replications can be executed under a different name in the same DBH as the original or in another DBH under an optional name. Replications can be added to the SQL database catalog in multiple DBHs for read access.
The database administrator can create and update replications of an original database from SESAM backup copies (catalog backups on disk or magnetic tape cartridge) or from a foreign copy (see section “Creating replications from foreign copies”) at any intervals. If necessary, he/she can deletes spaces from a replication or extends the replication with new spaces.
A replication which contains all the spaces of the original database (catalog space and all user spaces) is known as a complete replication. A partial replication contains the catalog space and at least one of the user spaces.
A complete replication can become a partial replication. Conversely, a partial replication can be extended to become a complete replication.
Replications and partial replications are available for read access. If a replication contains a partitioned table, all the partitions of the table must be contained in the replication. A partial replication must always be complete in itself, i.e. the partial replication must contain all the indexes for all the tables which belong to the partial replication.
A complete replication is created from a complete catalog backup via the utility statement CREATE REPLICATION.
A partial replication is created by:
the utility statement CREATE REPLICATION ... FOR SPACE ... from a complete catalog backup or a catalog backup without NO LOG index spaces
the utility statement CREATE REPLICATION ... from a catalog backup without NO LOG index spaces
the utility statement REFRESH REPLICATION ... FOR SPACE ... from a complete replication or a partial replication, for example, when logging was interrupted for a replication space in the original and this space can no longer be updated in the replication
the SQL statement CREATE SPACE which is used to create a new space in the original
The database administrator can extend a replication by adding user spaces of the original to the replication using the utility statement REFRESH SPACE on the basis of a backup. These spaces can be new to the replication or they may have previously belonged to the replication (“previous replication spaces”). The replication must be updated to such an extent that the backup used is known in the replication.
You can find information about current and previous replication spaces via the utility monitor, mask COP.4.6 (see “Utility Monitor” manual).
In order to be able to update a replication with REFRESH REPLICATION, all the replication spaces must be included in the logging and logging must have been interrupted (e.g. using LOAD OFFLINE). This also applies to spaces which are to be added to a replication using REFRESH SPACE.
As part of the media recovery, the database administrator can also use a replication as an alternative to SESAM backups to repair or reset an original database:
He/she can repair user spaces, the catalog space or an entire database with the aid of a replication (see section “Using a replication to repair an original database”). Under certain circumstances this may be faster than a normal RECOVER.
He/she can use the replication to reset user spaces, the catalog space or an entire database to the status of the replication (see section “Reset the original database using replications”).
He/she can create a new original database from the replication (see section “Creating a separate original database from the replication”).