abap 数据库表锁机制（ABAP database table lock mechanism）.docVIP

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abap 数据库表锁机制（ABAP database table lock mechanism）.doc

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abap 数据库表锁机制（ABAP database table lock mechanism）

abap 数据库表锁机制（ABAP database table lock mechanism） *---------------------------- overview of SAP ---------------------------- lock mechanism SAP, why do you want to set the lock: 1, to maintain data consistency If several users to access the same resources, we need to find a method to synchronize access to maintain data consistency. For example, in flight reservation system In the system, there is no need to check the empty seat, when the examination, you dont want others to modify important data (the number of empty seats). 2, only the Database lock is not enough The database management system for physical lock rows to be modified, other users can access the database until the lock is released this record. In the SAP system, when a new screen will release the Database lock screen because the change will trigger an implicit DB COMMIT . If the data is collected from several screens to it, and in this period of time the data will be locked separately, using only the Database lock is not enough. The SAP system has a global level in the application server LOCK TABLE, can be used to set the logical lock to lock the table entries, and The ENQUEUE process to manage the lock. SAP lock is a lock on the logical meaning, you may lock table entries in DATABASE simply Non-existent。 Two, the lock object and its corresponding Function Module Create a SE11 object in the lock, lock object must be custom named EZ or EY at the beginning. A lock object contains only a PRIMARY TABLE can contain several SECONDARY TABLE lock in three modes: E, S, X. LOCK PARAMETERS you have to fill in the root According to what fields to lock the table entry. E mode: when changes in the data set for the pattern. Model: S itself does not need to change the data, but the data do not want to show others change. Model X: similar to E, but does not allow the accumulation of monopoly. If you are successful for a lock object lock in a program, if the mode is E, other users cant lock on this object with E, X, S Any