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Difference between of CHECK DATA in ONLINE and ADMIN Operational state

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Difference between of CHECK DATA in ONLINE and ADMIN Operational state
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CHECK DATA in the ONLINE operational state

In the ONLINE operational state, the database system verifies the structural consistency of all LOB columns, tables, indexes, and so on, in the data and cache area.

Whenever the database system reads the data pages from the data area, it calculates a check sum which should correspond to the check sum stored on the page.

The database system goes through all B* trees and page chains once completely. It verifies whether all the pages in the B* trees or page chains can be reached, and whether the management structures on the pages are complete (for instance, the separators at the B* tree index level).

CHECK DATA SNAPSHOT in ONLINE operational state (only as of SAP MaxDB Version 7.9)

The database system creates a database snapshot before the CHECK DATA runs through all B* trees and page chains once on this converter version. It also verifies whether all the pages in the B* trees or page chains can be reached, and whether the management structures on the pages are all complete (for example, the separators at the B* tree index level).

Incase no errors occur for CHECK DATA SNAPSHOT, unlike the CHECK DATA (without SNAPSHOT) in the operational state ONLINE, the database system wipes out the converter utilizing the results of the checks: It removes all pages which it did not read during the checks and to which no further references currently exist in the converter.

CHECK DATA in the operational state ADMIN

Firstly, in the ADMIN operational state, the database system performs out the same checks as in the ONLINE operational state.

Incase no errors occur for this CHECK DATA, the database system utilizes the results of the checks to for cleaning the converter: It deletes all pages which it did not read during the checks and to which no further references currently exist in the converter.

If BAD indexes are identified during the CHECK DATA, the converter is not cleaned up. Therefore, the user needs to ensure that the indexes marked as BAD are again created before the database structure check is performed out in ADMIN operational state.