Controlling Update Access

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Controlling Update Access

Purpose of Physical Area Locks

Physical area locks prevent concurrent update by independent transactions (that is transactions executing outside of a single central version or data sharing group) and prevent update access to an area requiring recovery of incomplete transactions.

How Locking Works

CA IDMS/DB provides this protection as follows:

Protection Name	Description
Local mode	As each area is readied in any update mode, CA IDMS/DB checks the lock. If the lock is set, the transaction receives an error and access to the area is not allowed. If the lock is not set, the local mode transaction causes the lock to be set and the space management page is rewritten immediately. If the transaction terminates abnormally (that is, without issuing a FINISH or COMMIT WORK), the lock remains set. Further update access is prevented until the area is recovered (through CA IDMS recovery procedures).
Central version	At system startup, the central version checks the locks in all areas intended for update. If the physical lock is set and the area is not shared, or the area is shared but is not currently being updated by another member of the central version's data sharing group, then a warning message is displayed at the console and the area status is changed to offline. The central version proceeds without the use of that area and any transaction attempting to ready that area will receive an error. If the physical lock is subsequently removed from the area, the status of the area can be varied to update.

Protection Name

Description

Local mode

As each area is readied in any update mode, CA IDMS/DB checks the lock. If the lock is set, the transaction receives an error and access to the area is not allowed.

If the lock is not set, the local mode transaction causes the lock to be set and the space management page is rewritten immediately. If the transaction terminates abnormally (that is, without issuing a FINISH or COMMIT WORK), the lock remains set. Further update access is prevented until the area is recovered (through CA IDMS recovery procedures).

Central version

At system startup, the central version checks the locks in all areas intended for update. If the physical lock is set and the area is not shared, or the area is shared but is not currently being updated by another member of the central version's data sharing group, then a warning message is displayed at the console and the area status is changed to offline. The central version proceeds without the use of that area and any transaction attempting to ready that area will receive an error. If the physical lock is subsequently removed from the area, the status of the area can be varied to update.