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General Information
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Source
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{ORACLE_HOME}/rdbms/admin/dbmslock.sql
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First Available
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7.3.4
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Constants
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Name
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Description
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Data Type
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Value
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nl_mode
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NuLl
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INTEGER
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1
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ss_mode
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Sub Shared: used on an aggregate object to indicate that share locks are being acquired on subparts of the object
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INTEGER
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2
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sx_mode
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Sub eXclusive: used on an aggregate object to indicate that exclusive locks are being acquired on sub-parts of the object
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INTEGER
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3
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s_mode
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Shared: indicates that the entire aggregate object has a share lock, but some of the sub-parts may additionally have exclusive locks
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INTEGER
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4
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ssx_mod
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Shared SubeXclusive
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INTEGER
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5
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x_mode
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eXclusive
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INTEGER
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6
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Dependencies
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SELECT referenced_name
FROM dba_dependencies
WHERE name = 'DBMS_LOCK'
UNION
SELECT name
FROM dba_dependencies
WHERE referenced_name = 'DBMS_LOCK';
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Exceptions
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Error Number
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Description
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ORA-20000
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Unable to find or insert lock <lockname> into catalog dbms_lock_allocated.
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ORU-10003
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Unable to find or insert lock <lockname> into catalog dbms_lock_allocated.
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Object Privileges
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GRANT execute ON dbms_lock TO <schema_name>
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GRANT execute ON dbms_lock TO uwclass;
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ALLOCATE_UNIQUE
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Allocates a unique lock identifier (in the range of 1073741824 to 1999999999) given a lock name. Lock identifiers are used to enable applications to coordinate their use of locks
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dbms_lock.allocate_unique(
lockname IN VARCHAR2,
lockhandle OUT VARCHAR2,
expiration_secs IN INTEGER DEFAULT 864000);
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See dbms_lock demo
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CONVERT
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Converts a lock from one mode to another
Overload 1
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dbms_lock.convert(
id IN INTEGER,
lockmode IN INTEGER,
timeout IN NUMBER DEFAULT maxwait)
RETURN INTEGER;
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Return Values
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0
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Success
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1
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Timeout
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2
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Deadlock
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3
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Parameter error
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4
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Don't own lock specified by id or lockhandle
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5
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Illegal lock handle
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See dbms_lock demo
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Overload 2
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dbms_lock.convert(
lockhandle IN VARCHAR2,
lockmode IN INTEGER,
timeout IN NUMBER DEFAULT maxwait)
RETURN INTEGER;
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See dbms_lock demo
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RELEASE
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Explicitly releases a lock previously acquired using the REQUEST function
Overload 1
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dbms_lock.release(id IN INTEGER) RETURN INTEGER;
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Return Values
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0
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Success
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3
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Parameter error
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4
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Don't own lock specified by id or lockhandle
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5
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Illegal lock handle
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See dbms_lock demo
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Overload 2
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dbms_lock.release(lockhandle IN VARCHAR2) RETURN INTEGER;
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See dbms_lock demo
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REQUEST
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Requests a lock with a given mode
Overload 1
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dbms_lock.request(
id IN INTEGER,
lockmode IN INTEGER DEFAULT x_mode,
timeout IN INTEGER DEFAULT maxwait,
release_on_commit IN BOOLEAN DEFAULT FALSE)
RETURN INTEGER;
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Return Values
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0
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Success
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1
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Timeout
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2
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Deadlock
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3
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Parameter error
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4
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Don't own lock specified by id or lockhandle
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5
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Illegal lock handle
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See dbms_lock demo
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Overload 2
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dbms_lock.request(
lockhandle IN VARCHAR2,
lockmode IN INTEGER DEFAULT x_mode,
timeout IN INTEGER DEFAULT maxwait,
release_on_commit IN BOOLEAN DEFAULT FALSE)
RETURN INTEGER;
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See dbms_lock demo
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SLEEP
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Suspends the session for a given period of time
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dbms_lock.sleep(seconds IN NUMBER);
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exec dbms_lock.sleep(1.00);
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Demo
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-- create demo table
CREATE TABLE lock_test (
action VARCHAR2(10),
when TIMESTAMP(9));
GRANT insert ON lock_test TO public;
CREATE OR REPLACE PACKAGE lock_demo IS
v_lockname VARCHAR2(12) := 'control_lock';
v_lockhandle VARCHAR2(200);
v_result PLS_INTEGER;
-- obtain a lock
PROCEDURE request_lock(p_ltype INTEGER, p_retval OUT INTEGER);
-- release an existing lock
PROCEDURE release_lock(p_retval OUT INTEGER);
-- view the stored handle
FUNCTION see_handle RETURN VARCHAR2;
-- decode lock request
FUNCTION decode_req(p_result PLS_INTEGER) RETURN VARCHAR2;
-- decode lock release
FUNCTION decode_rel(p_result PLS_INTEGER) RETURN VARCHAR2;
END lock_demo;
/
CREATE OR REPLACE PACKAGE BODY lock_demo IS
PROCEDURE request_lock(p_ltype IN INTEGER, p_retval OUT INTEGER) IS
BEGIN
IF v_lockhandle IS NULL THEN
dbms_lock.allocate_unique(v_lockname, v_lockhandle);
p_retval := dbms_lock.request(v_lockhandle, p_ltype);
END IF;
END request_lock;
------------------------------------------------------------
PROCEDURE release_lock(p_retval OUT INTEGER) IS
BEGIN
IF v_lockhandle IS NOT NULL THEN
p_retval := dbms_lock.release(v_lockhandle);
END IF;
END release_lock;
------------------------------------------------------------
FUNCTION see_handle RETURN VARCHAR2 IS
BEGIN
IF v_lockhandle IS NOT NULL THEN
RETURN v_lockhandle;
ELSE
RETURN 'Not Allocated';
END IF;
END see_handle;
------------------------------------------------------------
FUNCTION decode_req(p_result PLS_INTEGER) RETURN VARCHAR2 IS
retval VARCHAR2(20);
BEGIN
SELECT DECODE(p_result,0,'Success',1,'Timeout',2,'Deadlock',
3,'Parameter Error',4,'Already owned',5,'Illegal Lock Handle')
INTO retval
FROM dual;
RETURN retval;
END decode_req;
------------------------------------------------------------
FUNCTION decode_rel(p_result PLS_INTEGER) RETURN VARCHAR2 IS
retval VARCHAR2(20);
BEGIN
SELECT DECODE(p_result,0,3, 'Parameter Error',4, 'Already owned',
5, 'Illegal Lock Handle')
INTO retval
FROM dual;
RETURN retval;
END decode_rel;
------------------------------------------------------------
END lock_demo;
/
GRANT execute ON lock_demo TO public;
set serveroutput on
-- get an exclusive lock in the current session (Session 1)
DECLARE
s VARCHAR2(200);
BEGIN
lock_demo.request_lock(6, s);
dbms_output.put_line(s);
END;
/
/* Two session request a shared lock (ss_mode). The shared lock cannot be acquired because session 1 holds an exclusive lock. Execution will stop on the request until the the exclusive lock is released. */
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Session 2
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Session 3
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set serveroutput on
DECLARE
s VARCHAR2(200);
BEGIN
uwclass.lock_demo.request_lock(
dbms_lock.ss_mode, s);
dbms_output.put_line(s);
INSERT INTO uwclass.lock_test
(action, when)
VALUES
('started', SYSTIMESTAMP);
dbms_lock.sleep(5);
INSERT INTO uwclass.lock_test
(action, when)
VALUES
('ended', SYSTIMESTAMP);
COMMIT;
END;
/
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set serveroutput on
DECLARE
s VARCHAR2(200);
BEGIN
uwclass.lock_demo.request_lock(
dbms_lock.ss_mode, s);
dbms_output.put_line(s);
INSERT INTO uwclass.lock_test
(action, when)
VALUES
('started', SYSTIMESTAMP);
dbms_lock.sleep(5);
INSERT INTO uwclass.lock_test
(action, when)
VALUES
('ended' , SYSTIMESTAMP);
COMMIT;
END;
/
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-- Session 1 releases its lock
DECLARE
s VARCHAR2(200);
BEGIN
lock_demo.release_lock(s);
dbms_output.put_line(s);
END;
/
-- Execution resumes when the exclusive lock is released
SELECT TO_CHAR(when,'dd.mm.yyyy hh24:mi:ss'), action
FROM lock_test
ORDER BY when;
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