ORA-04021: timeout occurred while waiting to lock object

问题

I have this anonymous PL/SQL block which calculates and prints a value return from a table.

DECLARE
    U_ID NUMBER :=39;
    RETAIL BINARY_FLOAT:=1;
    FLAG NUMBER;
BEGIN
    SELECT NVL(RETAIL_AMOUNT,1),UNIT_ID INTO RETAIL, FLAG FROM UNITS WHERE UNIT_ID=U_ID;
    LOOP
    SELECT NVL(MAX(UNIT_ID),U_ID) INTO FLAG FROM  UNITS WHERE FATHER_ID=FLAG;
    IF FLAG=U_ID THEN EXIT; END IF;
    SELECT RETAIL* RETAIL_AMOUNT INTO RETAIL FROM UNITS WHERE UNIT_ID=FLAG;
    EXIT WHEN FLAG=U_ID;
    END LOOP;
DBMS_OUTPUT.PUT_LINE( RETAIL);
END;

This block work correctly, but I wanted to do the same thing using a PL/SQL Function

I wrote the function as follow:

CREATE OR REPLACE FUNCTION GET_UNIT_RETAIL(U_ID NUMBER)
     RETURN NUMBER
IS
    RETAIL BINARY_FLOAT:=1;
    FLAG NUMBER;
BEGIN
    SELECT NVL(RETAIL_AMOUNT,1),UNIT_ID 
    INTO RETAIL, FLAG 
    FROM UNITS 
    WHERE UNIT_ID=U_ID;

    LOOP
        SELECT NVL(MAX(UNIT_ID),U_ID) 
        INTO FLAG 
        FROM  UNITS 
        WHERE FATHER_ID=FLAG;
        IF FLAG=U_ID THEN 
            EXIT; 
        END IF;
        SELECT RETAIL* RETAIL_AMOUNT 
        INTO RETAIL 
        FROM UNITS 
        WHERE UNIT_ID=FLAG;
        EXIT WHEN FLAG=U_ID;
    END LOOP;

    RETURN NUMBER;
END;
/

When I try to execute the above code to save the function to the database, the environment (SQL*PLUS) hangs for a long time and at the end returns this error:

ERROR at line 1:
ORA-04021: timeout occurred while waiting to lock object

What is the problem ??? Please !

回答1:

Sounds like ddl_lock problem

Take a look at
dba_ddl_locks to see who is "blocking" a create or replace.

Also try to create under different name - and see what happens.

回答2:

The problem was because the Object GET_UNIT_RETAIL was busy by other environment Here is the answer:

https://community.oracle.com/thread/2321256

来源：https://stackoverflow.com/questions/39051788/ora-04021-timeout-occurred-while-waiting-to-lock-object

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