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How to make sure Oracle Sequence in SP is called only from 1 thread / user at a time

Posted on 2009-05-04
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Last Modified: 2013-12-07
I have an SP which resets a Sequence to 1 and return the nextvalue to user.

How to handle race condition in here so following error is avoided.
exception ORA-08004 sequence
            COB_SEEQ_KITID.nextval goes below min value and cannot be instantiated
CREATE OR REPLACE PROCEDURE SP_GetNextKitID
(
        O_KitID             OUT NVARCHAR2
)
AS
BEGIN
 
        DECLARE
        v_Sequence         INTEGER;
        
        BEGIN
              
        SELECT COB_SEQ_KITID.NEXTVAL INTO v_Sequence FROM DUAL; 
        
        IF <some condition> THEN
            BEGIN
                EXECUTE IMMEDIATE ' ALTER SEQUENCE COB_SEQ_KITID INCREMENT BY '|| TO_CHAR (1 - v_Sequence);
                SELECT COB_SEQ_KITID.NEXTVAL INTO v_Sequence FROM DUAL;                
                EXECUTE IMMEDIATE 'ALTER SEQUENCE COB_SEQ_KITID INCREMENT BY 1';       
            END;
        END IF;     
 
        SELECT TO_CHAR(SYSDATE,'YY') ||TO_CHAR(SYSDATE,'DDD')|| LPAD(v_Sequence,5,'0') INTO O_KitID FROM DUAL;
    END;
END;

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Question by:thermalsun
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10 Comments
 
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Accepted Solution

by:
sdstuber earned 500 total points
ID: 24294888
see attached
ee.txt
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Author Comment

by:thermalsun
ID: 24295251
Can I trap that I values is going below minimum value of the sequence then use another value of reset?
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Expert Comment

by:sdstuber
ID: 24295409
yes, you can either define a pragma for that exception or check sqlcode in a when others clause of an exception block in your procedure

or you can avoid the error by checking the minimum value before trying to reset

select min_value from user_sequences where sequence_name = 'COB_SEQ_KITID';

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LVL 74

Expert Comment

by:sdstuber
ID: 24295413
if the sequences is owned by a different user you may need to use all_sequences or dba_sequences and specify the owner
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Author Comment

by:thermalsun
ID: 24302917
I created a package and used Locks but the system is not able to acquire lock..

what could be going wrong... pls help.
CREATE OR REPLACE PACKAGE FLXUSER."COB_KIT_SEQUENCE" 
AS  
    PROCEDURE reset_kitid_seq (v_SequenceOUT OUT INTEGER);      
END;
 
 
CREATE OR REPLACE PACKAGE BODY  "COB_KIT_SEQUENCE" 
AS  
lock_handle NUMBER := 1073741800;    
PROCEDURE RESET_KITID_SEQ (v_SequenceOUT OUT INTEGER)
IS    
    lock_status INTEGER;    
    v_LastRefresh DATE;
    v_Error EXCEPTION;
      
        BEGIN           
           v_SequenceOUT:=0;         
            
           lock_status := dbms_lock.REQUEST(lockhandle => lock_handle, lockmode => dbms_lock.x_mode);
 
           IF lock_status = 0 THEN
            SELECT LastUpdateOn INTO v_LastRefresh 
            FROM SEQUENCE_ 
            WHERE UPPER(NAME) = 'KITID';        
                
            SELECT COB_SEQ_KITID.NEXTVAL INTO v_SequenceOUT FROM DUAL; 
                
                IF TO_CHAR(v_LastRefresh,'DD/MM/YYYY') <> TO_CHAR(SYSDATE,'DD/MM/YYYY') THEN
                    BEGIN
                        EXECUTE IMMEDIATE ' ALTER SEQUENCE COB_SEQ_KITID INCREMENT BY '|| TO_CHAR (1 - v_SequenceOUT);
                        SELECT COB_SEQ_KITID.NEXTVAL INTO v_SequenceOUT FROM DUAL;                
                        EXECUTE IMMEDIATE 'ALTER SEQUENCE COB_SEQ_KITID INCREMENT BY 1';
                        UPDATE SEQUENCE_ SET NEXT_ = 2, LASTUPDATEON = SYSDATE, LASTUPDATEDBY = 'GetNextKitID'
                        WHERE UPPER(NAME) = 'KITID';
                    END;
                END IF;
                           
           ELSE
          
               RAISE v_Error;           
           END IF;
        
           lock_status := dbms_lock.release(lockhandle => lock_handle);
            
            EXCEPTION
            WHEN v_Error THEN raise_application_error (-20660, 'Failed to process sequence COB_SEQ_KITID');  
        END;       
    END;

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by:thermalsun
ID: 24303172
getting status = 3 (Parameter error).

Which parameter is incorrect !!
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Assisted Solution

by:sdstuber
sdstuber earned 500 total points
ID: 24303551
dbms_lock.release and request are overloaded

lockhandle should be a string that you have used "allocate_unique" to generate a number for.

if you just want to use the number, then use parameter ID instead.
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Author Comment

by:thermalsun
ID: 24305197
cool.. that a lot sdstuber for your help.

I got it working :)
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Author Closing Comment

by:thermalsun
ID: 31577489
Excellent and timely help  :)
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Expert Comment

by:sdstuber
ID: 24305287
Glad I could help!
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