Tuning and Best Practices Oracle PLSQL

7/30/2019 Tuning and Best Practices Oracle PLSQL

1/13

Copyright 1999 Steven Feuerstein, PL/Solutions Page 1

Oracle PL/SQL

Tuning and OptimizationTechniques

Quiz Problems and Solutions


2/13


Tuning Data Structures - Before

File: slowds_q1.sql

ALTER TABLE employee ADD info VARCHAR2(2000);

CREATE OR REPLACE PACKAGE comm_pkgIS

TYPE reward_rt IS RECORD (nm VARCHAR2(2000),sal NUMBER,

comm NUMBER);

TYPE reward_tt IS TABLE OF reward_rtINDEX BY BINARY_INTEGER;

END;/

CREATE OR REPLACE PROCEDURE fix_me (nmfilter IN VARCHAR2,comm_list IN OUT comm_pkg.reward_tt

)IS

v_nmfilter VARCHAR2(2000) NOT NULL := nmfilter;v_info VARCHAR2(2000);v_nth INTEGER;

indx INTEGER;

BEGINFOR indx IN comm_list.FIRST .. comm_list.LAST

LOOPv_nth := v_nth + 1;/*

|| Record date on which increase occurred; time is not

|| important. Job is run at noon and lasts 15 minutes.*/v_info :=

'Doubled ' || v_nth || 'th employee''s salary on ' ||SYSDATE || ' to ' || comm_list(indx).sal * 2;

IF UPPER (comm_list(indx).nm) LIKE UPPER (v_nmfilter)THEN

UPDATE employee

SET salary := comm_list(indx).sal * 2,info := v_info,

commission := comm_list(indx).commWHERE last_name = UPPER (comm_list(indx).nm);comm_list(indx).comm := 0;

END IF;

END LOOP;END;

/


3/13


Tuning Data Structures - After

File: slowds_a1.sql

/* 1. Move collection out of parameter list and into package spec */

CREATE OR REPLACE PACKAGE comm_pkgIS

TYPE reward_rt IS RECORD (nm VARCHAR2(2000),sal NUMBER,

comm NUMBER);

TYPE reward_tt IS TABLE OF reward_rtINDEX BY BINARY_INTEGER;

rewards reward_tt;

END;

/

CREATE OR REPLACE PROCEDURE fix_me (

nmfilter IN VARCHAR2)

IS/* 2. Use %TYPE whenever appropriate to reduce memory requirements

and improve robustness of code. */

/* 3. UPPER the name filter here and not in the loop. Remove NOT NULL constraint.*/

v_nmfilter CONSTANT employee.last_name%TYPE := UPPER (nmfilter);v_name employee.last_name%TYPE;

v_sal employee.salary%TYPE;

/* 4. Use PLS_INTEGER */

/* 5. Grab first row in table to do optimal scanning code. */

indx PLS_INTEGER := comm_pkg.rewards.FIRST;

/* 7. Date is not going to change, so capture and convert once. */

v_date CONSTANT VARCHAR2(10) := TO_CHAR (SYSDATE, 'MM/DD/YYYY');

/* 8. Use PLS_INTEGER */v_first PLS_INTEGER;

BEGIN

/* 9. Do explicit NOT NULL check here */

IF nmfilter IS NOT NULL

THENv_first := indx - 1;

LOOP

EXIT WHEN indx IS NULL;


4/13


/* 10. Move repeated operations to local variables. */

v_name := UPPER (comm_pkg.rewards(indx).nm);v_sal := comm_pkg.rewards(indx).sal * 2;

/* 11. Skip assignment to v_info; put in SQL directly. */

IF v_name LIKE v_nmfilterTHEN

UPDATE employee

SET salary = v_sal,info = 'Doubled ' || TO_CHAR (indx - v_first) ||

'th employee''s salary on ' ||

v_date || ' to ' || TO_CHAR (v_sal),commission = comm_pkg.rewards(indx).comm

WHERE last_name = v_name;comm_pkg.rewards(indx).comm := 0;

END IF;END LOOP;

END IF;END;/


5/13


Present Value Calculation

Package Specification and Util ities

File: presvalue.sql

CREATE OR REPLACE PACKAGE pv

I S/ * Tabl e st r uct ur e t o hol d t he l ease accumul at i ons. */TYPE pv_t abl e_t ype I S TABLE OF NUMBER( 9) I NDEX BY BI NARY_I NTEGER;pv_t abl e pv_t abl e_t ype;

PROCEDURE showt ab;PROCEDURE bui l d_l ease_schedul e1( di sp I N BOOLEAN : = FALSE) ;PROCEDURE bui l d_l ease_schedul e2( di sp I N BOOLEAN : = FALSE) ;PROCEDURE bui l d_l ease_schedul e3( di sp I N BOOLEAN : = FALSE) ;

END;

/CREATE OR REPLACE PACKAGE BODY pvI S

FUNCTI ON pv_of _f i xed (year I N I NTEGER) RETURN NUMBER I SBEGI N

/ * Dummy computat i on */RETURN ( year * 1. 25) ;

END;

FUNCTI ON pv_of _var i abl e ( year I N I NTEGER) RETURN NUMBER I SBEGI N

/ * Dummy computat i on */RETURN ( year / 1. 25) ;

END;

PROCEDURE showt ab I Si ndx I NTEGER;

BEGI N/ * Di spl ay t he r esul t s */i ndx : = pv_t abl e. FI RST;LOOP

EXI T WHEN i ndx I S NULL;DBMS_OUTPUT. PUT_LI NE (

' PV i n year ' | | i ndx | | ' = ' | | pv_tabl e( i ndx) ) ;i ndx : = pv_t abl e. NEXT ( i ndx) ;

END LOOP;END;


6/13


Present Value Calculation - Version 1File: presvalue.sql

PROCEDURE bui l d_l ease_schedul e1(di sp I N BOOLEAN : = FALSE)/ * Const r uct pr esent val ue l ease schedul e over 20 years. */I S

/ * Temporar y var i abl e t o hol d l ease accumul at i on. */pv_t ot al _l ease NUMBER( 9) ;

BEGI NFOR year_ count i n 1 . . 20LOOP

/ * Reset t he l ease amount f or t hi s year . */pv_t ot al _l ease : = 0;/ *| | Bui l d t he PV based on t he remai ni ng years

| | pl us t he f i xed and var i abl e amount s.*/FOR year_count 2 i n year_count . . 20LOOP

/ * Add annual t otal l ease amount t o cummul at i ve. */pv_t ot al _l ease : =

pv_t ot al _l ease +pv_of _f i xed ( year_count 2) +pv_of _var i abl e ( year _count 2) ;

END LOOP;

/ * Add t he annual PV t o the tabl e. */pv_t abl e ( year_count ) : = pv_t ot al _l ease;

END LOOP;

I F di sp THEN showt ab; END I F;END;

Hint for Tuning

Analyze the frequency of execution of the pv_of_* functions.


7/13



PROCEDURE build_lease_schedule2

(disp IN BOOLEAN := FALSE)IS

one_year_pv NUMBER(9) := 0;pv_total_lease NUMBER(9) := 0;

BEGIN/*|| Build the 20-year accumulated total and save each

|| of the annual lease amounts to the PL/SQL table. Notice that

|| pv_table (N) is set to the annual lease amount for year N-1.*/FOR year_count in 1 .. 20

LOOPone_year_pv :=

pv_of_fixed (year_count) + pv_of_variable (year_count);

pv_total_lease := pv_total_lease + one_year_pv;IF year_count < 20THEN

pv_table (year_count+1) := one_year_pv;END IF;

END LOOP;

/* Save the 20-year total in the first row. */

pv_table (1) := pv_total_lease;

/* For each of the remaining years... */

FOR year_count IN 2 .. 20LOOP

/* Subtract the annual amount from the remaining total. */

pv_total_lease := pv_total_lease - pv_table (year_count);

/*|| Save the Nth accumulation to the table (this writes right|| over the annual lease amount, which is no longer needed.

|| I get double use out of the pv_table in this way.*/

pv_table (year_count) := pv_total_lease;

END LOOP;

IF disp THEN showtab; END IF;

END;


8/13



PROCEDURE bui l d_l ease_schedul e3( di sp I N BOOLEAN : = FALSE)

I Spv_t ot al _l ease NUMBER( 9) : = 0;one_year _pv NUMBER( 9) : = 0;

BEGI NFOR year_count I N REVERSE 1. . 20LOOP

one_year_ pv : = pv_of _f i xed( year_ count ) +pv_of _var i abl e( year _count ) ;

pv_t otal _l ease : = pv_t otal _l ease + one_year_ pv;pv_t abl e ( year_count ) : = pv_t ot al _l ease;

END LOOP;

I F di sp THEN showt ab; END I F;END;


9/13


LStrip Function - Version 1File: lstrip1.sf

CREATE OR REPLACE FUNCTION lstrip1 (

string_in IN VARCHAR2,substring_in IN VARCHAR2,

num_in IN INTEGER := 1)RETURN VARCHAR2

ISBEGIN

IF num_in < 1

OR string_in IS NULL

OR substring_in IS NULLTHEN

RETURN string_in;

ELSIF INSTR (string_in, substring_in) = 1THEN

RETURN lstrip1 (

SUBSTR (string_in, LENGTH (substring_in) + 1),substring_in,num_in - 1

);ELSE

RETURN string_in;END IF;

END;

/


10/13



CREATE OR REPLACE FUNCTION lstrip2 (

string_in IN VARCHAR2,substring_in IN VARCHAR2,

num_in IN INTEGER := 1)RETURN VARCHAR2

ISretval VARCHAR2(32767);subnum INTEGER := 0;

sublen INTEGER := LENGTH (substring_in);

subpos INTEGER;BEGIN

retval := string_in;

WHILE (subnum < num_in)LOOP

subpos := INSTR (retval, substring_in, 1);

IF (subpos = 1)THEN

retval := SUBSTR (retval, sublen + 1);

subnum := subnum + 1;ELSE

subnum := num_in;END IF;

END LOOP;

RETURN retval;

END lstrip2;/

Commentary

The algorithm in this case uses a WHILE loop. For each iteration of the loop body, it checks to see if the

sub-string occurs at the beginning of the string. If so, that sub-string is stripped off using SUBSTR and

tested again. So which is the better implementation (version 1 or version2)? Neither is particularly longor complex. One should, however, always be concerned about the use of recursion, because it can be

very resource-intensive.

- Danny Wagenaar ([email protected]):


11/13



CREATE OR REPLACE FUNCTION lstrip3 (string_in IN VARCHAR2,

substring_in IN VARCHAR2,num_in IN INTEGER := 1)

RETURN VARCHAR2IS

v_length NUMBER;v_clip VARCHAR2(32767);v_clipcount INTEGER := 0;

BEGIN

v_length := LENGTH (substring_in);WHILE v_clipcount < num_inLOOP

v_clip :=SUBSTR (

string_in, v_clipcount * v_length + 1, v_length);

EXIT WHEN v_clip != substring_in;v_clipcount := v_clipcount + 1;

END LOOP;

RETURN SUBSTR (string_in, v_clipcount * v_length + 1);END;

/

Commentary

"We avoided the use of the char_in parameter in our implementation. We were careful not to userecursion to make sure there would be no problem with nesting depth. Also, we do not use INSTR to see

if the substring_in is at the beginning of string_in, since this could potentially lead to a search through32767 bytes for a nonexistent pattern.

"My new solution to the lstrip problem is significantly faster than the one I sent yesterday when used to

strip large numbers of substrings from the input string. It is also much faster on stripping small

iterations, although that is not really noticeable to the user unless the function is called a lot. On top ofthat, the code is smaller while maintaining readability."

- Ken Geis and Jay Weiland ([email protected] [email protected])


12/13


DBMS_SQL Binding Optimization

Large Volume of BindingFile: slowsql_q2.sql

CREATE OR REPLACE PROCEDURE bindall

IScur INTEGER := DBMS_SQL.open_cursor;

rows_inserted INTEGER;

BEGIN

DBMS_SQL.parse (

cur,'INSERT INTO emp (empno, deptno, ename)

VALUES (:empno, :deptno, :ename)',DBMS_SQL.native);

FOR rowind IN 1 .. 1000LOOP

DBMS_SQL.bind_variable (cur, 'empno', rowind);

DBMS_SQL.bind_variable (cur, 'deptno', 40);DBMS_SQL.bind_variable (cur, 'ename', 'Steven' || rowind);

rows_inserted := DBMS_SQL.execute (cur);

END LOOP;

DBMS_SQL.close_cursor (cur);

END;

/


13/13


Maybe We Can Avoid Binding Altogether!

File: slowsql_a2.sql

CREATE OR REPLACE PROCEDURE bindnoneIS

cur INTEGER := DBMS_SQL.open_cursor;

rows_inserted INTEGER;

BEGINDBMS_SQL.parse (

cur,'BEGIN

INSERT INTO emp (empno, deptno, ename)

VALUES (myvars.empno, myvars.deptno, myvars.ename);

END;',DBMS_SQL.native

);

FOR rowind IN 1 .. 1000

LOOPmyvars.empno := rowind;myvars.deptno := 40;

myvars.ename := 'Steven' || rowind;

rows_inserted := DBMS_SQL.execute (cur);END LOOP;

DBMS_SQL.close_cursor (cur);END;/

Run the slowsql_a2.tst to compare the performance.

Tuning and Best Practices Oracle PLSQL

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