Dan Hotka’s PL SQL Tips and Techniques, Part II

EMBARCADERO TECHNOLOGIESEMBARCADERO TECHNOLOGIES
PL/SQL Tips & Techniques Part II
Scott Walz | Embarcadero Director of Software Consultants
Dan Hotka |Author & Instructor |Oracle Ace Director

EMBARCADERO TECHNOLOGIES
PL/SQL Tips and Techniques
• Rapid SQL
– PL/SQL Templates
• Read my blogs
– Live demo of using the Result Cache!
• PL/SQL Tips
– Packages
– Compiler Options
• PL/SQL Limits
• Includes some useful performance Tips for Functions

Recap: PL/SQL Tips and Techniques Part 1
• PL/SQL Architecture
• PL/SQL IF-THEN-ELSE and CASE
• Profiler
• Debugger
• Introduction to Result_Cache
Why do we
use PL/SQL?

PL/SQL Overview
• Procedure
– Does processing
– Returns a code that the work was successful or not
– May or may not be passed values
– May or may not return values
• Functions
– Similar to Procedure EXCEPT it does return a value!
• Packages
– Grouping related procedures and functions
– Can share cursors/work areas
– Code inheritance
– When one module is accessed…entire package is loaded into Oracle

Packages
• Packages
– Organizing related procedures and functions
– Allows for sharing of resources
– Allows for overloading of procedures/functions
• Can have a varchar2 or a date function with same name
– Can be used to hide code
– Read into the library cache as a unit
• Packages can be pinned in the library cache

Packages
• Packages have 2 parts:
– Specification (or header)
• Defines the package name
• Declares the visible packages and procedures
• Defines the common variables, exceptions, types, and cursors to
be shared by objects in the package
– Body
• Contains PRAGMA declarations
• Contains all procedures and functions
– Procedures and functions NOT listed in the spec are ‘private’, used
only in this package, code is not easily visible
– Public procedures/functions are displayed via DESCRIBE

Packages
• Syntax: CREATE [or replace] PACKAGE <pkg name>
[AUTHID {DEFINER | CURRENT_USER }]
IS <proc/functions by name IN OUT vars>
[PRAGMA Declarations]
END;
CREATE [or replace] PACKAGE BODY <same pkg name>
IS <proc/functions by name IN OUT vars with code>
<object, exception, variables, cursors>
[PRAGMA Declarations]
END <same pkg name>;

Packages
• Pragma Declarations
– Compiler directives
– Autonomous Transactions
• Run in separate transaction
• Declared only in the package body
– Serially_Reusable
• Reset global/public variables back to initial state
• Declared in both the package spec and body

Packages

Package Body

Package Body (continued)

• Optional Block
– BEGIN appears after all other definitions (at the end of the
package body)
– Used to load arrays, perform package startup-tasks, etc

. . .
FUNCTION fahrenheit_to_celsius (IN_Temp NUMBER)
RETURN NUMBER IS
. . .
END fahrenheit_to_celsius;
BEGIN
var1 := 1;
var2 := 2;
END temperature;
/

Rapid SQL and Packages
• Templates!
– Right Click on Package…opens both
– Edit  Create Package …basic syntax

Oracle 11g Query Result Cache
• IF same function called with same in_vars
• Enhances Oracle8i thru Oracle10 DETERMINISTIC
• SQL with /*+ RESULT_CACHE */ hint
• Function with RESULT CACHE syntax
– RELIES_ON (table1, table2, …) – optional table DML check
• Deprecated in Oracle11r2
• First result cache returned instead of rerunning the function/SQL!

• Results stored in the SGA (Result Cache Memory)
• Any session running the function/SQL can benefit!
– * Enterprise Edition of Oracle
• Good for any table that is queried more than it is updated
– Result Cache is flushed with an update
Poll Question: Do you use functions? Would this be of use to you?

• Query Result Cache Sizing and
Monitoring
– Sizing via Init.Ora settings:
• RESULT_CACHE_MAX_SIZE
– 0 disables it
– Size in bytes in increments of 32K [num
G | M | K ]
– Initially defaults to 10% Shared Pool Size
• RESULT_CACHE_MAX_RESULT
– 0 – 100
– Percentage of
RESULT_CACHE_MAX_SIZE single result
can take
– Dynamic performance views:
• V$RESULT_CACHE_STATISTICS
• V$RESULT_CACHE_MEMORY
• V$RESULT_CACHE_OBJECTS
• V$RESULT_CACHE_DEPENDENCY

• RESULT_CACHE from function calls
– IF same function called with same in_vars
– First result cache returned instead of rerunning the function!
– Results stored in the SGA…any session running the function can
benefit!
SQL> create or replace function get_dname
(in_deptno number) return in_dname varchar2
RESULT_CACHE
As
…
SQL> select get_dname(10) DNAME from dual;
SQL>
DNAME
-----------
CHICAGO
SQL> Time: 00.00.01
SQL> select get_dname(10) DNAME from dual;
SQL>
DNAME
-----------
CHICAGO
SQL> Time: 00.00.00

First Execution

Next Execution

User1 - 5 executions

Dept Table Updated
Rt Click on DEPT Table
Edit Data
or
Generate Statement
 INSERT

User0 - 5 executions

• RESULT_CACHE from SQL
– IF same SQL ran from any session:
• First result cache returned instead of rerunning the SQL!
• Appears to work with bind variables
– Init.Ora settings:
• RESULT_CACHE_MODE [MANUAL | FORCE]
– Manual…must use RESULT_CACHE hint
– FORCE…always uses result cache unless NO_RESULT_CACHE used
USER1
SQL> select /*+RESULT_CACHE */ ename from emp;
SQL>
ENAME
-----------
SMITH
SQL> Time: 00.00.10
SQL>
USER2
SQL> select /*+RESULT_CACHE */ ename from emp;
SQL>
ENAME
-----------
SMITH
SQL> Time: 00.00.00
SQL>

Be careful out there!
– Make sure the SQL inside the function does not have other
dependencies
• Such as a SYSDATE or some other variable NOT passed in as an in
variable
• Can probably fix about ANY problem by putting the dependencies
as in variables!

PL/SQL Limits
• PL/SQL Limits (Oracle11 and before)
– Program/Variable Name – 30 characters
– PL/SQL Block Nesting – 255
– Bind Variables passed – 32K
– Record Nesting – 32
– Record Limit – 64K
– Sub Query Nesting – 254
– Trigger size 32K
Memory Footprint:
Select * from USER_OBJECT_SIZE
Where NAME = ‘<procedure/function/package name>’;

PL/SQL Limits
• PL/SQL
– Varchar2 – 32K
– Char – 32K
• IF selecting/saving to database fields
– Always specify a SIZE…
– Manage sizes with SUBSTR
– Change database data type to CLOB
– Unmanaged: Ora-12899: value too large for column
• SQL
– Varchar2 – 4000 bytes
– Char – 2000 bytes

New Limits
• Increased column size limits in Oracle12
– IF MAX_STRING_SIZE = EXTENDED
• Varchar2 – new limit 32K
• NVarchar2 – new limit 32K
• RAW – new limit 32K
– MAX_STRING_SIZE = STANDARD (default behavior)
• Varchar2 –limit 4K
• NVarchar2 –limit 4K
• RAW – limit 2K
Oracle Database 12c New Features pg 228 - 229

New Limits
Database Type Current Table Limit Current PL/SQL Limit Oracle12c New
Limit
Varchar2 4K 32K 32K
Nvarchar2 4K 32K 32K
Raw 2K 32K 32K

New Limits
• New Oracle12 init.ora setting: Max_String_Size
– Set to EXTENDED
• Allows new limits
– Set to STANDARD
• Old limits used
– Indexes only support keys up to 6,400 bytes long
– THERE IS NO GOING BACK!!!
• Backup well/test then implement.

Course Materials
• Additional Reading
– Book: Oracle12c Database
New Features
– Author: Robert Freeman

Questions
34

Thank you for attending!
Connect with us Online
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http://community.embarcadero.co
m/index.php/article/articles-
database
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Dan Hotka’s PL SQL Tips and Techniques, Part II

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