Oracle DBA Basics 2

8/8/2019 Oracle DBA Basics 2

1/19

Overview of Oracle Database 10gOverview of Oracle Database 10g

Srinivasan.KSrinivasan.K

[email protected]

1


2/19

2

Agenda

Oracle Index

Table Partitions

Oracle Enterprise Manager

Analysing SQLQueryplans


3/19

3

Oracle Index

Whatisanindex ?

An index is a performance-tuning method ofallowing faster retrieval of records.

An index creates an entry for each value thatappears in the indexed columns.

By default, Oracle creates B-tree indexes.

TypesofIndex

B-Tree index

Bitmap index


4/19

4

Oracle Index

B-Tree index

B(inary)-Tree Indexes are used on HIGH CARDINALITYcolumns (i.e. columns which have relatively large numberofdistinct values) or on HIGH SELECTIVITY columns (i.e.columns having the capability to filter-out majority of therows when used in a WHERE clause).

Examples of high SELECTIVITY columns are Primary keycolumns & columns having relatively less number ofduplicate values.

For instance, if a table has 1, 00,000 records and one of itsindexed columns have 81,000 distinct values, and then theselectivity of the index is 0.81. Ideal selectivity for anindexed column is 1 (which is true in the case of primarykey indexes).

'


5/19

5

Oracle Index

Syntax :

CREATE [UNIQUE] INDEX index_name ON table_name (column1,column2,.column_n);

For example :

CREATE INDEX supplier_idx ON supplier(supplier_name);

Bitmap Index

A bitmap index is a type of index that uses a string of bits toquickly locate rows in a table

Bitmap indexes are normally used to index low cardinalitycolumns in a warehouse environment.

Syntax :

CREATE BITMAP INDEX on();

cont'd


6/19

6

For example :

CREATE BITMAP INDEX emp_bitmap_idx

ON big_emp(sex);

Table partitions

Partitioning enables tables and indexes to besubdivided into smaller manageable pieces andthese each small piece is called a "partition".

From an "Application Development" perspective,

there is no difference between a partitioned and anon-partitioned table.

The applicationneednot be modified to access apartitioned table if that application was initiallywritten on a non partitioned tables.

Cont'd

Table partitions


7/19

7

Table partitions

Advantagesofusing Partitionsin Table

Smaller and more manageable pieces ofdata (Partitions)

Reduced recovery time

Failure impact is less Faster access ofdata

Very easy to use.

TypesofPartitioning Methods:

Range partitioning

Hash partitioning

List partitioning

cont'd


8/19

8

Table partitions

Range partitioning

This type of partitioning is useful whendealing with datathat has logical ranges into which it can be distributed

Range partitions requires scalarnumeric values.

Performance is best when the data evenly distributesacross the range.

Forexample :

CREATE TABLE emp (

empno NUMBER(4),

ename VARCHAR2(30),

sal NUMBER )

PARTITION BY RANGE(empno) (

partition e1valueslessthan (1000) tablespace ts1,

partition e2 valueslessthan (2000) tablespace ts2,

partition e3valueslessthan (MAXVALUE)tablespace ts3); comt'd


9/19

9

Table partitions

Listpartitioning

List partitioned is used when you require explicitcontrol over how rows map to partitions.

Specify a list ofdiscrete values for the partitioning

column in the description for each partition.List partitioning allows partitioning by non-scalardata.

Forexample :

CREATE TABLE myemp_work ( empno NUMBER PRIMARYKEY,

ename VARCHAR2(30),

salary NUMBER(8,2),

deptno NUMBER)

PARTITION BYLIST (deptno)

( PARTITION p10 VALUES (10),

PARTITION p20 VALUES (20),


10/19

10

Table partitions

Hashpartitioning

Partitions is based on a hashing algorithm

Evenly distributing data between the partitions.

This is typically used where ranges aren't appropriate, i.e.

customernumber, product ID

Forexample :

CREATE TABLE sales_hash

(salesman_id NUMBER(5),

salesman_name VARCHAR2(30),

sales_amount NUMBER(10),week_no NUMBER(2))

PARTITION BY HASH(salesman_id)

PARTITIONS4

STORE IN (data1,data2,data3,data4);

The preceding statementcreatesatable sales_hash,whichishashpartitioned

onsalesman_idfield. The tablespace namesare data1,data2,data3,anddata4. Cont'd


11/19

11



Perform administrative tasks such as creating schemaobjects (tablespaces, tables, and indexes).

Managing user security, backing up and recovering your

database, and importing and exporting data.

View performance and status information about thedatabase instance.

Installationsteps

Loginasoracle userindbserver. Execute the below

commands.$ emctlstopdbconsole

$ emca-deconfig dbcontroldb-reposdrop

$ emca-config dbcontroldb-reposcreate

(or)

$ emca-config dbcontroldb-reposrecreate

cont'd


12/19

12


13/19

13


14/19

14

Analysing Query plans

What is an explain plan ?

The EXPLAIN PLAN statementdisplays executionplanschosenbythe Oracle optimizerforSELECT, UPDATE,

INSERT,and DELETE statements.A statement's executionplanisthe sequence ofoperationsOracle performstorunthe statement.

How to generate an explain plan ? sqlplus "/ assysdba"

sql > @$ORACLE_HOME/sqlplus/admin/plustrce.sql

sql > grant PLUSTRACE touser;

sql > GRANT UNLIMITED TABLESPACE TOuser;

sql > @?/rdbms/admin/utlxplan.sql

sql > GRANT ALLON sys.plan_table TOpublic;

sql > create publicsynonymplan_table forsys.plan_table;

connuser/user

setautotrace traceonly explain

select * from emp;


15/19


16/19

16

Analysing Query plans

Example 2

EXPLAIN PLAN SET statement_id = 'example_plan2'FORSELECT full_name FROM per_all_people_f

WHERE full_name LIKE 'Pe%';

Plan---------------------------------------------

SELECT STATEMENTTABLE ACCESSBY INDEX ROWID PER_ALL_PEOPLE_FINDEX RANGE SCAN PER_PEOPLE_F_N54

Thisplanshows executionofaSELECT statement.* Index per_people_f_n54isusedinarange scanoperation.* The table per_all_people_fisaccessedthrough ROWID. ROWIDsareobtainedfromthe index inthe previousstepforkeysthatmeetthe WHEREclause criteria.Whenthe table isaccessed,anyadditionalWHERE clauseconditionsthatcouldnotbe evaluatedduring the range scan (because thecolumnispresentinthe table andnotinthe index)are also evaluated.

* The SELECT statementreturnsrowssatisfying the WHERE clauseconditions (evaluatedinprevioussteps).

'


17/19

17

Topics/References

Oracle Index

ttp://www.lorentzcenter.nl/

ttp://www.techonthenet.com/

Table Partitions

ttp://www.oracle-dba-online.com/

ttp://www.oracle-base.com/

Oracle Enterprise Managerttp://download.oracle.com/

Analysing SQLQueryplans

ttp://www.oracle-base.com/


18/19

18

Q & A


19/19

19

THANKS

Oracle DBA Basics 2

Documents

Transcript of Oracle DBA Basics 2