Oracle9i Supplied PL/SQL Packages and Types Reference Release 2 (9.2) Part Number A96612-01 |
|
Oracle Lock Management services for your applications are available through procedures in the DBMS_LOCK
package. You can request a lock of a specific mode, give it a unique name recognizable in another procedure in the same or another instance, change the lock mode, and release it.
Because a reserved user lock is the same as an Oracle lock, it has all the functionality of an Oracle lock, such as deadlock detection. Be certain that any user locks used in distributed transactions are released upon COMMIT
, or an undetected deadlock may occur.
User locks never conflict with Oracle locks because they are identified with the prefix "UL". You can view these locks using the Enterprise Manager lock monitor screen or the appropriate fixed views. User locks are automatically released when a session terminates.
The lock identifier is a number in the range of 0 to 1073741823.
Some uses of user locks:
This chapter discusses the following topics:
DBMS_LOCK
is most efficient with a limit of a few hundred locks for each session. Oracle strongly recommends that you develop a standard convention for using these locks in order to avoid conflicts among procedures trying to use the same locks. For example, include your company name as part of your lock names.
There might be operating system-specific limits on the maximum number of total locks available. This must be considered when using locks or making this package available to other users. Consider granting the EXECUTE
privilege only to specific users or roles.
A better alternative would be to create a cover package limiting the number of locks used and grant EXECUTE
privilege to specific users. An example of a cover package is documented in the DBMSLOCK.SQL
package specification file.
nl_mode constant integer := 1; ss_mode constant integer := 2; -- Also called 'Intended Share' sx_mode constant integer := 3; -- Also called 'Intended Exclusive' s_mode constant integer := 4; ssx_mode constant integer := 5; x_mode constant integer := 6;
These are the various lock modes (nl -> "NuLl", ss -> "Sub Shared", sx -> "Sub eXclusive", s -> "Shared", ssx -> "Shared Sub eXclusive", x -> "eXclusive").
A sub-share lock can be used on an aggregate object to indicate that share locks are being aquired on sub-parts of the object. Similarly, a sub-exclusive lock can be used on an aggregate object to indicate that exclusive locks are being aquired on sub-parts of the object. A share-sub-exclusive lock indicates that the entire aggregate object has a share lock, but some of the sub-parts may additionally have exclusive locks.
When another process holds "held", an attempt to get "get" does the following:
maxwait constant integer := 32767;
The constant maxwait
waits forever.
|
Copyright © 2000, 2002 Oracle Corporation. All Rights Reserved. |
|