Running Global Projects
Updates and Synchronisation
: Reverse Propagation Prevention
Reverse Propagation Prevention
When a database update is initiated, a check is automatically made to make sure that the update direction is correct. If the check implies that the propagation is in the reverse direction (that is from out-of-date database to up-to-date database) the update is aborted and an error message 'Prevented reverse update' or 'Prevented reverse copying' is displayed. Note that this check cannot be made if the primary location is being changed.
The check involves an analysis of the status of the two databases. The result of the analysis determines the appropriate propagation direction. This propagation direction is compared with that expected at the primary location and the update is allowed to continue only when these propagation directions are the same.
The database status that is analysed comprises a Non-additive Changes Count (NACCNT), Header Changes Count (HCCNT), Claim List Changes Count (CLCCNT) and the Latest Session. The three counts are pseudo-attributes of the DB element, and can be queried.
The message 'Prevented reverse update' means that the session data or the header page at the secondary location is greater than at the primary location. This may be investigated by checking the session number at each location, and, if necessary, by querying the HCCNT attribute at the DB elements of the databases.
The message 'Prevented reverse copying' means that the NACCNT at the secondary location is greater than at the primary location. This attribute may be queried at the DB element of the database at each location.
It may be necessary to recover the database at the secondary location to solve the problem.
If either of the above messages is reported for a system or Global database, a similar investigation can be made. For a system database the HCCNT and NACCNT attributes should be queried at the STAT /*S element. For a Global database, they should be queried at the GSTAT /*GS element.
To resolve the problem, the database at the appropriate location must be recovered.
Refer to
Recovery from Reverse Propagation Errors
for further information.
1974 to current year.
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