Oracle PL/SQL Best Practices – Part 2

John Mullinsjmullins@themisinc.com

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Presenter

John Mullins Themis Inc. (jmullins@themisinc.com) 30+ years of Oracle experience Oracle Certified Professional DBA Certified Technical Trainer Over 300 classes taught

Themis Inc.

More than 25 years in the industry More than 90,000 students have attended a

Themis training event Courses:

DB2, SQL Server, Oracle, Unix, Linux, Java, Web Development, .NET and many more

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Related Themis Courses

Introduction to Oracle PL/SQL Programming June 26

Oracle Advanced PL/SQL Programming June 29

Troubleshooting, Debugging and Tuning Oracle PL/SQL Programs May 8, 2017

Webinar Objectives

To become familiar with suggested best practices related to performance and troubleshooting when coding Oracle PL/SQL programs

1 – Use the PL/SQL Profiler

Enables the collection of performance data Information Gathered:

The total number of times each line has been executed

The total amount of time that has been spent executing that line

The minimum and maximum times that have been spent on a particular execution of that line

The PL/SQL Profiler

The dbms_profiler package START_PROFILER procedure STOP_PROFILER procedure

Identify “hot” spots in your PL/SQL code Identify starting points for further tuning efforts

DBMS_PROFILER Usage

Easy to use Steps:

Start the profiler Execute application code Stop the profiler Examine the profiler data

PLSQL_PROFILER_DATATEXT TOTAL_OCCUR TOTAL_TIME LINE

------------------------------------------------------- ----------- ------------- ----------

...

...v_calculated_value(read_data%ROWCOUNT) := ((12.34 50000 .045677 18

/2.91) / i.id) + (3.41 * i.id /1.179);

FOR i IN 1..50000 LOOP 50001 .004041 21

INSERT INTO forall_2 VALUES (v_id(i), v_calculate 50000 .726758 22

d_value(i));

FOR i IN 1..50000 LOOP 50000 .014334 25

UPDATE forall_2 50000 57.191248 26

FOR i IN 40001..50000 LOOP 10000 .002895 31

DELETE FROM forall_2 10000 11.872791 32

COMMIT; 1 .000136 35

END; 1 .000909 36

2 – Be Aware of the PL/SQL Optimizer Settings

Enabled by default Can rearrange code PLSQL_OPTIMIZE_LEVEL parameter ALL_PLSQL_OBJECT_SETTINGS data

dictionary view

PLSQL_OPTIMIZE_LEVEL

Parameter Controls automatic optimizations Valid values: (0-3) Default value is 2

3 - Tune the SQL First

Use typical SQL tuning methods Explain Plan utility Good indexing Up to date object statistics SQL Tuning Advisor

4 – Use the Result Cache Where Appropriate

Cache stores entire result sets in shared memory Reduces reads

PL/SQL Function with Result Cache

CREATE OR REPLACE FUNCTION AVG_SAL_DEPT (v_deptno IN NUMBER)

RETURN NUMBER RESULT_CACHE ISv_avg NUMBER;

BEGINSELECT avg(sal) INTO v_avgFROM empWHERE deptno = v_deptno;

RETURN v_avg; END;/

5 - Subprogram Inlining

Subprogram inlining replaces a subprogram invocation with a copy of the invoked subprogram If the invoked and invoking subprograms are in the

same program unit Be aware of the PLSQL_OPTIMIZE_LEVEL

setting

6 – Give Data Types Some Thought

Use PLS_INTEGER or SIMPLE_INTEGER instead of NUMBER for computations

Be aware of PLSQL_CODE_TYPE setting INTERPRETED NATIVE

7 – Passing Parameters and the NOCOPY Clause

Pass the corresponding actual parameter by reference instead of value

The NOCOPY clause requests that the compiler pass the corresponding actual parameter by reference instead of value

8 – Reduce Context Switches

A context switch occurs every time the PL/SQL engine calls the SQL engine to parse, execute, or fetch from a cursor. This increases CPU time. This increases logical reads.

Goal: Reduce context switches.

When to Consider Bulk Binds

A PL/SQL program that reads thousands of rows or more from a cursor or performs that many similar INSERT/UPDATE/DELETE statements will most likely benefit from bulk binds.

Bulk Binding Benefits

Bulk Binds enable a PL/SQL program to fetch many rows from a cursor in one call instead of fetching one row at a time.

They also allow many similar DML statements to be executed with one call instead of requiring a separate call for each.

The Need for Arrays

Bulk Binds use arrays to carry many rows of data between the PL/SQL program and the database.

Any array type is ok. Associative Arrays VARRAYS Nested Tables

Reading with Bulk CollectBEGINOPEN read_orders;FETCH read_ordersBULK COLLECT INTO v_order_ids, v_order_totals;

SELECT order_id, order_totalBULK COLLECT INTO v_order_ids, v_order_totalsFROM product_order;

DML with Bulk BindsFORALL i IN 1..v_order_ids.COUNT

UPDATE product_order SET order_total = v_order_totals(i)-(v_order_totals(i)*.10)WHERE order_id = v_order_ids(i);

Summary

Following best practices helps promote consistent, reliable, readable, easier to maintain PL/SQL code along with possible performance gains

Questions? jmullins@themisinc.com

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Thank you for attending. Have a good day.