This section explains illegal table accesses in the upgrade subsystem during the execution of a Zero Downtime Option (ZDO) maintenance event.
The upgrade subsystem must only perform changes on tables that are cloned. All tables that are classified as shared tables must not be changed by the upgrade subsystem. Structural changes cannot be kept unidentified as the table classification algorithm in phase RUN_RSPTBFIL_ZDM_CLASSIFY calculates the delta between source and target structure of all tables known in the ABAP Data Dictionary. Hence, no illegal table access can happen by a structural change.
However, if table content in shared tables is changed from the upgrade subsystem, the upgrade procedure detects an illegal table access and the transaction fails.
Note
Technically, the write access on shared tables from the upgrade subsystem is prevented. If a write access on such a shared table happens, a short dump occurs. This ensures that the bridge subsystem running does not see data that belongs to the target release written by the upgrade subsystem.
Illegal table access can happen in different ways:
- An application-defined procedure (AIM, XPRA, or XCLA) tries to write into a table that is not declared in the ZDO enablement.
- Someone logged on to the upgrade subsystem and performed manual activities.
In both cases, the illegal table access is recorded in an internal control table. At the end of the ZDO procedure, shortly before restarting the system, SUM checks if illegal table access happened. If SUM finds illegal table access, phase RUN_CHECK_ILLACCESS will stop with an error that cannot be skipped and an incident at SAP is required.