ORACLE 11g SQL PL/SQL Performance Enhancements Developers

New performance features for Developers

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11g new performance features for DevelopersA Knowledge Transfer session

Nikos Plevris, Principal Service Delivery Manager, November 2009


Agenda

• SQL and PL/SQL performance improvement and scalability• New and Enhanced

• Functionality

• Structures

• Objects

• The Developer’s approach


Automatic “Native” PL/SQL Compilation

• Previous releases: PL/SQL interpreted to C code, then compiled by 3rd party compiler or DLL loader

• 11g: PL/SQL source code is directly translated to the DLL for the server, bypassing the file system directories by doing the linking and loading itself.

• Initialization parameter: plsql_code_type• [NATIVE | INTERPRETED]

• Dynamic change:• alter system | alter session• alter procedure <PROC> compile plsql_code_type=native;

• DBA_PLSQL_OBJECT_SETTINGS view

20% improved performance With native PL/SQL compilation:

The Whetstone Benchmark shows

that real native compilation is

two-and-a-half times faster than

C native compilation.


Adaptive Cursor Sharing1

• Parameter cursor_sharing := [EXACT|SIMILAR|FORCE]

• Bind peeking – Optimizer evolves execution plan during first hard parse of bind variables

• 11g adaptive cursor sharing – Optimizer generates multiple execution plans for a statement that uses bind variables


Adaptive Cursor Sharing2

• Allows for intelligent cursor sharing for statements that use bind variables

• Is used to compromise between cursor sharing and optimization

• Has the following benefits:• Automatically detects when different executions

would benefit from different plans

• The optimizer avoids expensive table scans and index searches based on selectivity criteria thus speeding up data retrieval

• Automated mechanism that cannot be turned off


Adaptive Cursor Sharing3 - Architecture


Adaptive Cursor Sharing4 – Dictionary Views


Adaptive Cursor Sharing Demo


SQL Query Result Cache1

• Cache the result of a query or query block for future use (SQL query and PL/SQL function results)

• Cache is used across sessions and statements unless it is stale

• Benefits:• Scalability

• Reduction of memory usage and I/O

• Good candidate statements:• Access many rows

• Return few rows

200% improved performance for read-intensive workload Part of SGA shared pool (~1% of shared_pool_size up to 75%) or(0.25% of memory_target) or(0.50% of sga_target)


Setting Up SQL Query Result Cache2

• At the instance level using parameter RESULT_CACHE_MODE. Values are:

• AUTO: The optimizer decides to cache based on repetitive executions

• MANUAL: Use hint result_cache• FORCE: All results are stored in the cache

• At table level:

Three new init parameters result_cache_mode result_cache_max_size result_cache_max_result

Dynamic parameters:ALTER SYSTEM SET

result_cache_mode = ‘AUTO’;


Setting Up SQL query result cache3

• At the session level:• ALTER SESSION SET result_cache_mode=FORCE;

• At the statement level – Queries, subqueries and inline views:

• Hints result_cache_mode and no_result_cache

Using the hint

PL/SQL code


Administer SQL query result cache4

• Use DBMS_RESULT_CACHE package:

• View SQL Query cache dictionary information:


Result Query Cache Demo


Considerations on query result cache5

• The result cache is disabled for queries containing:

• Result cache does not release memory:

• Bind variables:


Sequences in PLSQL

• Sequence calls directly into statements without first querying them from the dual pseudotable

• In 11g, the usage of the pseudocolumns CURRVAL and NEXTVAL make writing PL/SQL source code easier and improve run-time performance and scalability.

• The usage of sequence_name.CURRVAL and sequence_name.NEXTVAL can be utilized whenever a number expression is used.

CREATE TABLE seq_table (sequencing_id NUMBER);

CREATE SEQUENCE sequencing_s1;

-- In Oracle 10g you would use a sequence value in a PL/SQL block as follows:

DECLAREsequence_value NUMBER;BEGINSELECT sequencing_s1.nextval INTO sequence_value FROM dual;INSERT INTO seq_table VALUES (sequence_value);COMMIT;END;/

--While this syntax still works in Oracle 11g, you can now simplify it by using:

BEGININSERT INTO seq_table VALUES (sequencing_s1.nextval);COMMIT;END;/


Next-Generation LOBs• 11g provides two storage implementations

for LOB columns:• BASICFILE = Pre-Oracle 11g CLOBs, BLOBs

• SECUREFILE = New LOB storage implementation

• Prerequisites• automatic segment space management

(compatible 11.0.0.0.0)

• Benefits• Faster LOB Retrieval

• ODP.NET now makes fewer round trips to the database server to retrieve LOB information. ODP.NET LOB retrieval performance is now faster

• Queries in SQL*Plus now support BLOB columns.

• Reduce space consumption

• Enhanced Security

create table secure_docs

( document_id number not null primary key,

name varchar2(255) not null,

edba_knowledgebase_category_id number not null,

mime_type varchar2(128),

doc_size number,

dad_charset varchar2(128),

last_updated date,

content_type varchar2(128),

blob_content blob)

tablespace tools

lob (blob_content) store as securefile (

tablespace tools enable storage in row chunk 8192 pctversion 10 nocache logging)


Compound trigger1

• Easier to program one trigger to fire at various timing points instead of multiple simple triggers each fires at single timing point.

• Has a section for each of the BEFORE STATEMENT, BEFORE EACH ROW, AFTER EACH ROW, and AFTER STATEMENT timing points.

• Improved usability for the PL/SQL programmer and improved runtime performance and scalability:

• accumulate rows destined for a second table so that you can periodically bulk-insert them

• To avoid the mutating-table error (ORA-04091)

• Can be defined on either a table or a view

• Only DML statements trigger compound triggers

CREATE [OR REPLACE] TRIGGER trigger_name

FOR {INSERT | UPDATE | UPDATE OF column1

[, column2 [, column(n+1)]] | DELETE}

ON table_name

COMPOUND TRIGGER

[declaration_statement;]

BEFORE STATEMENT IS[declaration_statement;]BEGINexecution_statement;

END BEFORE STATEMENT;

BEFORE EACH ROW IS[declaration_statement;]BEGINexecution_statement;

END BEFORE EACH ROW;

AFTER EACH ROW IS[declaration_statement;]BEGINexecution_statement;

END AFTER EACH ROW;

AFTER STATEMENT IS[declaration_statement;]BEGINexecution_statement;END AFTER STATEMENT;

END [trigger_name];

/


Compound trigger2

• They DO NOT fire when:• the DML statement doesn’t change any rows AND• the trigger hasn’t implemented at least a BEFORE

STATEMENT or AFTER STATEMENT block.

• The declaration section executes before any timing-point sections execute. Variables and subprograms declared in this section have firing-statement duration.

• Support filtering actions :• Instead of the WHEN clause, use the UPDATE OF

column name filter as a governing event in updates.• Implement EXCEPTION blocks in any of the subordinate

timing point blocks

• The :new and :old pseudo-records can be used in the row-level statement blocks

• Requires at least one timing-point block.

CREATE [OR REPLACE] TRIGGER trigger_name

FOR {INSERT | UPDATE | UPDATE OF column1

[, column2 [, column(n+1)]] | DELETE}

ON table_name

COMPOUND TRIGGER

[declaration_statement;]

BEFORE STATEMENT IS[declaration_statement;]BEGINexecution_statement;

END BEFORE STATEMENT;

BEFORE EACH ROW IS[declaration_statement;]BEGINexecution_statement;

END BEFORE EACH ROW;

AFTER EACH ROW IS[declaration_statement;]BEGINexecution_statement;

END AFTER EACH ROW;

AFTER STATEMENT IS[declaration_statement;]BEGINexecution_statement;END AFTER STATEMENT;

END [trigger_name];

/


Compound Trigger Demo


Additional PL/SQL enhancements

• Native dynamic SQL now supports statements bigger than 32K characters by allowing a CLOB argument

• Increased in functionality of string functions: REGEXP_INSTR, REGEXP_SUBSTR, REGEXP_COUNT

• CONTINUE statement

• Minimum need to recompile dependent PL/SQL packages or view after an online table redefinition. ONLY if logically affected


Online Index creation-rebuild and Invisible indexes

• Online index creation and rebuild prior to this release (like 10g) required a DML-blocking exclusive lock at the beginning and end of the rebuild for a short period of time. This meant that there would be two points at which DML activity came to a halt.

• This DML-blocking lock is no longer required, making these online index operations fully transparent.

• Invisible index – Not being visible to the cost optimizer during execution plans

• test the usefulness of a new index without affecting execution plans

• Temporary purposes

The SHARED EXCLUSIVE locking strategy

applies to:

• create index online• rebuild index online• create materialized view log

Invisible index:• CREATE index <idx_name> invisible• ALTER index <idx_name> invisible;• DBA_INDEXES.visibility column

Use hint to force index use• Select /*+index ( <table> <idx> */ FROM ..

At the instance level – Init parameteroptimizer_use_invisible_indexes = FALSE


Partitioning Enhancements1

• Extended Composite Partitioning• Range-Hash (available since 8i)

• Range-List (available since 9i)

• Range-Range

• List-Range

• List-Hash

• List-List

• Extended composite partitioning allows data to be partitioned along two dimensions

CREATE TABLE list_hash_tab ( id NUMBER, code VARCHAR2(10), description VARCHAR2(50), created_date DATE)PARTITION BY LIST (code)SUBPARTITION BY HASH (id)( PARTITION part_aa values ('AA') ( SUBPARTITION part_aa_01, SUBPARTITION part_aa_02 ), partition part_bb values ('BB') ( SUBPARTITION part_bb_01, SUBPARTITION part_bb_02 ));


Extended Composite Partitioning Demo



• Interval Partitioning• automate the creation of range partitions by

creating partitions on demand

• Considerations:• Restricted to a single partition key that must be

a numerical or date range

• At least one partition must be defined when the table is created

• A MAXVALUE partition cannot be defined for an interval partitioned table

• NULL values are not allowed in the partition column

CREATE TABLE interval_tab ( id NUMBER, code VARCHAR2(10), description VARCHAR2(50), created_date DATE)PARTITION BY RANGE (created_date)INTERVAL (NUMTOYMINTERVAL(1,'MONTH'))( PARTITION part_01 values LESS THAN (TO_DATE('01-NOV-2007','DD-MON-YYYY')));


Interval Partitioning Demo



• System Partitioning• Allows large tables to be broken down into

smaller partitions

• There are no partitioning keys, system partitions have no bounds for ranges or lists

• Explicitly specify the rows to the target table partition using partition-aware syntax

• Benefits• The application controls the data placement and

how it is retrieved

• Db has no control over row placement – No partition pruning

CREATE TABLE system_partitioned_tab (

id NUMBER, code VARCHAR2(10), description VARCHAR2(50), created_date DATE)PARTITION BY SYSTEM( PARTITION part_1, PARTITION part_2);

INSERT INTO system_partitioned_tab PARTITION (part_1) VALUES (1, 'ONE', 'One', SYSDATE);

DELETE FROM system_partitioned_tab PARTITION (part_2) WHERE id = 1;

UPDATE system_partitioned_tab PARTITION (part_1) SET code = 'TWO' WHERE id = 2;



• Reference Partitioning• Relies on existing parent-child relationships and

is enforced by an active primary key and foreign key constraint

• The child table automatically inherits the partitioning key from the parent table without duplicating the key columns

• Use the keywords PARTITION BY REFERENCE (foreign_key name) as part of your create table statement

CREATE TABLE parent_tab (

id NUMBER NOT NULL,

code VARCHAR2(10) NOT NULL,

description VARCHAR2(50),

created_date DATE,

CONSTRAINT parent_tab_pk

PRIMARY KEY (id))

PARTITION BY RANGE (created_date)

( PARTITION part_2007 VALUES

LESS THAN (TO_DATE('01-JAN-2008',

'DD-MON-YYYY')),

PARTITION part_2008 VALUES

LESS THAN (TO_DATE('01-JAN-2009',

'DD-MON-YYYY')));

CREATE TABLE child_tab (

id NUMBER NOT NULL,

parent_tab_id NUMBER NOT NULL,

code VARCHAR2(10),

description VARCHAR2(50),

created_date DATE,

CONSTRAINT child_tab_pk PRIMARY KEY (id),

CONSTRAINT child_parent_tab_fk

FOREIGN KEY (parent_tab_id)

REFERENCES parent_tab (id))

PARTITION BY REFERENCE (child_parent_tab_fk);


The other approach: DBA ‘s view

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ORACLE 11g SQL PL/SQL Performance Enhancements Developers

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