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Definition

The lock table is a table in the main memory of the enqueue server that records the current locks in the system. For each elementary lock, the table specifies the owner, lock mode, name, and the fields in the locked table.

Use

The lock table is used to manage locks. Every time the enqueue server receives a lock request, the system checks the lock table to determine whether the request collides with an existing lock (see Lock Collisions). If this is the case, the request is rejected. Otherwise, the new lock is written to the lock table.

Structure

Each elementary lock corresponds to a data record in the lock table.

The structure of the lock entries is shown below.

This graphic is explained in the accompanying text

The individual field have the following meaning:

Field

Contents and meaning

Owner_1

Owner id and cumulation counter of owner_1: the ID contains the computer name, the work process, and a timestamp. It is also used to identify the SAP LUW. The cumulation counter specifies how often the owner has already set this elementary lock.

Owner_2

The above applies here to owner_2

Backup Id

Backup Id (index indicating where the lock entry is stored in the backup file) and backup flag (0 (no backup) or 1 (backup)).

Elementary lock

Lock mode

S (Shared lock, read lock)

E (Exclusive lock, write lock)

X (eXclusive lock, extended write lock, cannot be cumulated)

Name

Name of the database table in which fields are to be locked

Argument

Locked fields in the database table (linked key fields, can also contain wildcards)

Integration

The lock entries can be viewed for diagnosis purposes. This is described in the section entitled Managing Lock Entries.

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