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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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Accepted Solution

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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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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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Author Comment

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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