How to Calculate Procedures peformance - oracle

Question

Hi to everyone please suggest me how to check in the following among three method which is the best method and which method gives best performance.
Thanks in adavance.
CREATE OR REPLACE PACKAGE PKG_P
AS
G_SAL NUMBER(7,2):=&G;
END;
1.)NORMAL CURSOR FOR LOOP METHOD :
CREATE OR REPLACE PROCEDURE P(
v_deptno NUMBER,
v_dname VARCHAR2
)
AS
CURSOR c_emp(c_deptno NUMBER,c_dname VARCHAR2)
IS
SELECT E.Ename,D.Dname,E.Sal
FROM Emp E,Dept D
WHERE E.Deptno=D.Deptno
AND
E.Deptno=c_deptno
AND
D.Dname=c_dname
AND
E.Sal=PKG_P.G_SAL ;
BEGIN
FOR i IN c_emp(v_deptno,v_dname)
LOOP
DBMS_OUTPUT.PUT_LINE(i.Ename||' '||i.Dname||' '||i.Sal);
END LOOP;
END;
2)NORMAL CURSOR FOR LOOP WITH IF CONDITION :
CREATE OR REPLACE PROCEDURE P(
v_deptno NUMBER,
v_dname VARCHAR2
)
AS
CURSOR c_emp(c_deptno NUMBER,c_dname VARCHAR2)
IS
SELECT E.Ename,D.Dname,E.Sal
FROM Emp E,Dept D
WHERE E.deptno=D.deptno
AND
E.Deptno=c_deptno
AND
D.Dname=c_dname;
BEGIN
FOR i IN c_emp(v_deptno,v_dname)
LOOP
IF i.sal=PKG_P.G_SAL THEN
DBMS_OUTPUT.PUT_LINE(i.Ename||' '||i.Dname||' '||i.Sal);
END IF;
END LOOP;
END;
3)USING ASSCOCIATE ARRAY:
CREATE OR REPLACE PROCEDURE P(
v_deptno NUMBER,
v_dname VARCHAR2
)
AS
CURSOR c_emp(c_deptno NUMBER,c_dname VARCHAR2)
IS
SELECT E.Ename,D.Dname,E.Sal
FROM Emp E,Dept D
WHERE E.deptno=D.deptno
AND
E.Deptno=c_deptno
AND
D.Dname=c_dname;
TYPE t is RECORD
(
v_ename VARCHAR2(30),
v_dname VARCHAR2(30),
v_sal NUMBER(7,2)
);
TYPE t1 IS TABLE OF t;
t2 t1;
BEGIN
OPEN c_emp(v_deptno,v_dname);
FETCH c_emp BULK COLLECT INTO t2;
FOR i in t2.FIRST..t2.LAST
LOOP
IF t2(i).V_sal=PKG_P.G_SAL THEN
DBMS_OUTPUT.PUT_LINE(t2(i).v_ename||' '||t2(i).V_dname||' '||t2(i).V_sal);
END IF;
END LOOP;
END;

Answer 1

Easy answer: IT DEPENDS
With some time I could probably create some tables for you, where each of the three versions could be faster, because skewed data can confuse the optimizer...
But as general guidelines with not to strange data:
With newer Oracle Versions the first will be the fastest, easiest to read and overall best, With older versions you may have to incorporate BULK COLLECT into the first:
You should always give the optimizer as much information as you can - so all conditions should be in WHERE clause, so it can find the best plan. Also you don't want to read data from disk just to throw it away afterwards (loop with IF)
The second performance killer are PL/SQL context-switches. If you process one row at a time you will get an overhead for fetching each row individually - so you should use BULK COLLECT to read a bunch of data into memory and process them at once. But Oracle will automatically bulk collect cursor FOR-LOOPS since 10g. See this Link: CURSORS IN PLSQL
You should RARELY use BULK COLLECT without limit. What if the Cursor returns 10M rows? Without limit your whole memory will be flooded and your server will choke. So you would fetch in batches of about 100-500 rows (which newer oracle versions will do automatically with the FOR IN... Loop)