Creating Extracts

Extracts can be created at any authorized Location: the parent extract must be allocated to the Location first.

Like other databases in a Global project, extracts have a primary Location, and this need not be the same as the Primary location of the parent database. By default, the primary location of the new extract will be the current location.

• If the user is at the Hub and creating an extract for a satellite, use the AT option in the CREATE command. The extract will be created with its primary location at the Satellite specified.

• If the user is at an administering location, the user must also use the AT option to specify that the extract will be created at the administered location, otherwise the extract will be created at the administering location (that is, the true current location, queried using Q CURLOC). The parent extract must be allocated to the administered location.

• When creating an Extract at a satellite, make sure the CREATE EXTRACT command is given only once and check that the command has completed by issuing a Q DB dbname command. The user can issue further CREATE EXTRACT commands provided that the user does not use the same db name or db number (if specified). The daemon will assign a db number (dbno) if none is specified.

The CREATE EXTRACT command will be executed by the Daemon (which will imply a delay in executing the command) if any of the following is true:

• If the master database is primary somewhere else

• If the current location is a satellite

• If the parent extract is primary at another location

• If the new child extract is specified to be primary at another location (AT loc option).

  Note:
  An in-built recovery operation exists for CREATE EXTRACT and, therefore, the PREVOWNER command is not usually needed after a failure of the CREATE EXTRACT command. However, the automatic recovery operation does not cover the CREATE command Allocate operation and PREVOWNER may be needed in the unlikely event of this failing.

  Note:
  The ALLOCATE command allows child extracts to be allocated to a satellite without their parent being allocated, but the user will not be able to open the extract until all its ancestors have been allocated to the location. Also note that the ancestor extracts may need to be synchronised, if timed updates of extracts has not been implemented.

Extract creation is controlled by the NOEXTC attribute of a location. If this is TRUE, then extract creation is disabled and extracts cannot be created by that location. However the Hub or its administering location (if authorised) may create extracts.

The purpose of the NOEXTC attribute is to prevent a satellite from creating databases on the fly without authorization, and it applies to the administering location, not the administered location. However, if the HUB is doing it, it is by definition authorized. Thus the HUB is always able to create extracts.

Similarly, we could have a situation where one satellite AAA is administering another BBB. Satellite AAA might have NOEXTC false, and BBB might have NOEXTC true. In this case, AAA would be allowed to create extracts for itself and for satellite BBB.

But BBB would not be allowed to create any extracts itself. The screenshots below show how to set the NOEXTC attribute in the Modify Location window.