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Table locking

Former Member
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Hi all,

This is my question:

If a user locked a table in data base from one Application server then how other Application servers will come to know?

rgds

vinnu.

Accepted Solutions (0)

Answers (2)

Answers (2)

Former Member
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Vinnu,

Oracle maintains all locks as enqueues. The enqueue mechanism keeps track of users waiting for locks that are held by others and the lock mode these users require. The enqueue mechanism also keeps track of the order in which users requested the locks.

There are five basic table lock modes within an Oracle system. For DML transactions, some lock modes are automatically assigned. Each lock mode has a different level of restrictiveness that will be used to determine the modes on the table that other transactions can obtain.

A lock can be either exclusive or shared. Queries are always allowed on a structure, even a locked one, but other activities may be prevented. In exclusive mode, the data structure remains locked, preventing the resource from being shared with any other transaction until the lock is released. If you are performing an update of a row in a table, no one else will be able to modify that specific row until you have issued a rollback or commit command. Until you commit your change, Oracle will present a consistent view of that row as it appeared before you started to change it.

With shared locks, more than one transaction can hold a shared lock on a structure at the same time since shared locks are set at the table level for DML transactions.

The Enqueue Server administers the locks in the Lock Table. Have a look on Relationship Between SAP Locks and Database Locks in help.sap.com

Regards

Vinod

Former Member
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Locking mechanism is handled by Central Intance, not application server.

for more details follow http://help.sap.com/saphelp_nw2004s/helpdata/en/7b/f9813712f7434be10000009b38f8cf/frameset.htm

Cheers,

-Sunil