Oracle Database Administration
Introduction
Basic administration
Additional information
• http://technet.oracle.com - for developers and
administrators, available for:
– Download of Oracle products
– Download and viewing of product documentation
• http://www.mini.pw.edu.pl/~maczewsk/oracle
– Presentations from the lecture
– Lab tasks
Lecture plan
• Part 1 – basic database administration:
– creating database objects: users, tables, indexes,
tablespaces, datafiles etc.
– managing database objects
– networking, connecting to remote databases
– SQL language – SQL standard and Oracle
extensions
– programming Oracle – PL/SQL language
– exporting and importing data
Lecture plan cont.
• Part 2 – performance tuning:
– database instance parameters (e.g.: memory)
– tuning individual database components (log
buffers, undo space)
– tuning SQL statements (obtaining execution plan,
creating indexes, using hints)
Lecture plan cont.
• Part 3 – backup and recovery:
– Physical data storage
– Offline and online backups
– Restoring database from backup
– Recovering database after hardware failure or user
error
– Managing standby database
Introduction to the
Oracle Database
Oracle History
• 1978 – Oracle V1, never officially released
• 1980 – Oracle V2 released, written in
assembly language
• 1994 – Oracle 7 for PC released
• 1998 – Support for Linux platform
• 1999 – Oracle 8i with Java integration
• 2001 – Oracle 9i – modern Oracle
• 2004 – Oracle 10g
• 2007 – Oracle 11g
• 2013 – Oracle 12c
Oracle database
• The best database for large database systems:
– most reliable in terms of data safety
– highest availability
– scalable
– good internationalization support
• Oracle shortcomings:
– price – expensive
– speed – not the fastest database available
– amount of resources consumed
Data safety
• Many features that ensure safety of data:
– multiplexing of important database files
– writing changes to data files and to special log
files. Log files are used to recover database after
software or hardware failure
– archiving of log files. Archived log files can be
written to backup location(s)
– protection from human errors:
• possibility to view data from some point in time in the
pas
• possibility to use backup and perform point in time
recovery
Availability
• Very high availability:
– online backups – without shutting down the database
– most administrative tasks can be performed while the
database is running and available for users, for example:
analyzing, rebuilding indexes, moving data
– disk failure: it is possible to turn off and recover only the
part of the database that was affected by the failure, the rest
of the database can continue running
– parameters that ensure that recovery after failure will take
no more than the specified time
– standby database – second database that can be opened if
the main database fails
Scalability
• Oracle can handle unlimited amount of data:
– no limit on number of rows, number of tables etc.
– no limit on total size of the database
• Oracle runs on various operating systems:
– Windows NT/XP
– Linux
– Solaris, HP-UX, AIX
• Oracle Cloud/Grid – single database on a
cluster
Internationalization
• Database supports multiple languages/locales:
– sorting of text can be done in client language order
– date, time and currency is client dependent
– character set conversion – database running in utf8
or iso8859-2 will convert data for clients using
windows-1250
• Internally database can store data in Unicode
Oracle editions
• Express edition:
– Simple installation and administration, some
features are not available (for example: Java
Virtual Machine is disabled)
• Standard edition:
– Most frequently used features are available
• Enterprise edition:
– All features, very expensive
Speed of the database
• Oracle favors data safety over speed:
– it is not possible to disable some features to
achieve greater speed (e.g.: transactions)
– some other databases (e.g. MySQL) are faster than
Oracle
Resources consumed
• Oracle consumes large amounts of resources:
– new, empty database – at least 200MB, usually over 1GB
– at least 256MB RAM
• Hint: when installing Oracle on private
computer (Windows):
– install Standard or Enterprise edition
– assign around 256MB RAM for Oracle
– install database normally
– change startup of Oracle services to manual
– when required start the database manually with:
oradim –startup –sid database_sid
Oracle terminology - database
• Database – data stored on disk (data files and
some additional files)
• Database instance – program (group of
programs) that opens the database (disk files)
and makes it available to users
• User connects to the database instance and
retrieves data or requests changes to the
database
• When running Oracle on a cluster, there are
multiple database instances that open the same
database
Oracle terminology - schema
• Schema – set of objects (tables, indexes, views) that
belong to a database user.
– In Oracle SCHEMA = USER
– When new user is created (CREATE USER command),
initially it has an empty schema
– When the user logs in and creates new table, the table is
added to his schema
– When user issues:
SELECT * FROM some_table
Oracle looks for some_table in the user’s schema
– It is possible to access data in some other schema:
SELECT * FROM some_user.some_table
Major differences from other
database systems
Single database
• Many other database systems (Postgres,
MSSQL) can have multiple databases opened
by a single database engine
– each application can use separate database for its
data
• In Oracle single Oracle Instance can open one
database
– normally on a single database server there will be
only one database
– each application can store its data in separate user
schema
Data storage
• Many other database systems (Postgres,
MySQL) store table data in a separate file or
group of files
• Oracle stores table data in a tablespace.
Multiple tables are normally stored in the same
tablespace. Tablespace can be stored in one or
more data files (physical disk files)
Transactions
• Oracle executes every statement in a
transaction
– there is no command to start a transaction (like
BEGIN TRANSACTION)
– transaction is started automatically with a first
statement after COMMIT or ROLLBACK
– usually transaction must be finished manually with
COMMIT, exceptions:
• it is possible to turn on AUTOCOMMIT (by default:
disabled)
• some statements commit the transaction automatically:
all CREATE, ALTER, DROP and TRUNCATE
statements
Transaction example
-- user connects to the database
DELETE FROM table1;
-- new transaction created
INSERT INTO table1 VALUES (1, ‘some text’);
INSERT INTO table1 VALUES (2, ‘some text’);
CREATE TABLE table2
(
id NUMBER PRIMARY KEY,
text VARCHAR2(256)
);
ROLLBACK; -- table1 contains 2 rows,
-- the rollback statement rolled
-- back empty transaction
Date format, language
• Oracle has no fixed date and time format.
When displaying dates, Oracle uses the format
consistent with the connected client
• Language used by Oracle (for example: error
messages) also depend on the language
settings
• To use English with Oracle, set the
environment variable NLS_LANG before
starting SQLPlus:
– SET NLS_LANG=AMERICAN_AMERICA.UTF8
General database terminology
• Database user – login and password used to connect
to the database. Each user has:
– set of privileges for accessing the database
– schema objects: objects: tables, indexes etc.
• Table – database object used for data storage:
– can have any number of rows
– has fixed number of columns, each column has a name and
datatype
– can have constraints, indexes and relations to other tables
• Relation – defines a dependency between two tables
• Constraint – rule that must be satisfied by each
table row. Constraint can be:
– PRIMARY KEY constraint
– NOT NULL constraint
– UNIQUE constraint
– FOREIGN KEY constraint (relation)
– CHECK constraint
• Index – object that organizes data in a table.
Indexes are used:
– to enforce PRIMARY KEY and UNIQUE
constraints
– to improve query performance
• Trigger – action performed when user makes
changes to database data
• Session – single connection to the database.
One user can open multiple sessions to the
database
• Transaction – set of operations that are visible
as single (atomic) operation on the database.
Transaction belongs to a single open database
session.
Accessing the database
• Oracle can be accessed from various tools:
– Oracle tools:
• SQLPlus (always available) – command line tool for
executing SQL statements. All administrative statements
can be executed from SQLPlus
• SQL Developer – free development tool, easier to use
than SQLPlus
– Third party tools:
• TOAD –application for administrating Oracle database,
executing SQL statements, TOAD Freeware Edition is
available for free
Connecting to the database
• In order to connect, you need to specify:
– user name
– password
– connect string (optional)
– connect mode (optional)
• Connect string:
– determines location of the database, if not
specified – local database
• Connect mode – specified for administrative
connections (database startup and shutdown)
Starting database session
• The following commands will start SQLPlus
and connect to the database:
– sqlplus test/testpass – Log in as user “test”
password “testpass” to local database
– sqlplus test/testpass@db – Log in as user
“test” to database “db”
– sqlplus system/orclstudent – Log in as user
“system” password “orclstudent”
– sqlplus sys/orclstudent as sysdba – Log in
as user “sys” with special SYSDBA privileges
Networking
Connecting to Oracle
• Connection to Oracle is possible:
– in local mode – when connecting to local database
only
– via network – when connecting to some other
database
• All non-local connections are done through the
listener
The listener
• Oracle Listener is separate from the database
• In Windows it starts as service
OraclexxxxTNSListener
• One listener can handle connections for
multiple databases
• Listener configuration determines how clients
will connect to the database. By default
listener:
– uses TCP/IP
– listens on port 1521 – default Oracle port
Listener configuration
• Listener configuration is in
$ORACLE_HOME/network/admin/listener.ora
• Example configuration:
LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)
(HOST = host_name)(PORT = 1521))
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC0))
)
)
Listener startup and shutdown
• Listener can be started manually from the
command line:
– lsnrctl start
• Other commands:
– lsnrctl stop – stops the listener
– lsnrctl status – shows list of services that
this listener supports
Naming configuration
• When connecting to database using SQLPlus
you specify:
– user name
– password
– database name
• When the database name is empty –
connection to the local database
• When the database name is not empty – lookup
of the database name. By default database
names are looked up in tnsnames.ora file
tnsnames.ora
• Location:
$ORACLE_HOME/network/admin/tnsnames.ora
• This file is used to lookup names of databases:
– IP address of the database
– listener port number
– name of the Oracle instance
tnsnames.ora - example
• Typical entry in the tnsnames.ora file:
TEST =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = name_or_ip)
(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = database_instance_name)
)
)
tnsnames.ora - example
• Entries in tnsnames.ora enable:
– specifying multiple addresses for a connection (connect
time failover)
– request load balancing between the list of available
addresses
TEST =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = name_or_ip)
(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = other_host)
(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = database_instance_name)
)
)
tnsnames.ora - example
• Load balancing example
TEST =
(DESCRIPTION =
(ADDRESS_LIST =
(LOAD_BALANCE=on)
(FAILOVER=off)
(ADDRESS = (PROTOCOL = TCP)(HOST = name_or_ip)
(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = other_host)
(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = database_instance_name)
)
)
Database administration
Administrative privileges
• Database administration requires strong
privileges:
– SYSDBA – the most powerful database privilege,
enables database startup, shutdown and access to
all data in the database
– SYSOPER – enables database startup and
shutdown without access to database data
– DBA – role (a group of privileges) giving user full
administrative access, but without the right to start
and shut down the database
Administrator accounts
• Each Oracle database has two accounts:
– SYS – owner of the administrative objects, created
with DBA role, has SYSDBA and SYSOPER
privileges
– SYSTEM – automatically created with DBA role
• SYS and SYSTEM users should not be used to
create any tables
DBA, SYSDBA and SYSOPER
• DBA role grants administrator access to the
database when the database is running
• DBA role is not enough to startup and
shutdown the database
• SYSDBA and SYSOPER enable database
startup and shutdown
• In order to use the SYSDBA or SYSOPER
privilege, the connection must be in special
mode:
connect sys/sys_password as sysdba
Important!
• SYSDBA is not database user name – it is a
privilege and special connect mode.
• When connecting to the database:
connect sys/sys_password as sysdba
special connection with in SYSDBA mode is
requested.
SYSDBA and SYSOPER
• DBA user can be granted SYSDBA or SYSOPER
privilege
• SYSDBA privilege enables you to
– Perform STARTUP and SHUTDOWN operations
– ALTER DATABASE: open, mount, back up, or change
character set
– CREATE DATABASE
– DROP DATABASE
– CREATE SPFILE
– ALTER DATABASE ARCHIVELOG
– ALTER DATABASE RECOVER
– Includes the RESTRICTED SESSION privilege
– SYSDBA lets you look at any user’s data
Database shutdown
• SHUTDOWN NORMAL – waits for all users
to disconnect, not recommended – can take a
long time
• SHUTDOWN TRANSACTIONAL – waits
for all users to finish their transactions
• SHUTDOWN IMMEDIATE – rolls back all
uncommitted transactions, closes all sessions,
closes the database and shuts down the
instance
• SHUTDOWN ABORT – aborts the instance,
does not close the database properly. Requires
automatic recovery after startup.
Database startup
• Database startup involves 3 steps:
– starting the instance
– mounting the database
– opening the database – opened database is
available for use
• STARTUP – executes those 3 steps
• When performing administrative actions, those
steps can be performed one by one:
– STARTUP NOMOUNT – only start the instance,
useful when creating the database
– STARTUP MOUNT – start the instance and
mount the database (open database control files)
Database startup
• Example startup (rarely used):
– STARTUP NOMOUNT
– ALTER DATABASE MOUNT
– ALTER DATABASE OPEN
• Example startup (used for many administrative
actions):
– STARTUP MOUNT
– perform some administrative actions, e.g. recover
the database, change archiving mode
– ALTER DATABASE OPEN – opens database for
use
System views
• Oracle provides many system views that
provide information about the database:
– v$session – all open sessions
– v$datafile – all data files
– v$logfile – all log files
– v$database – general information about the
database
– v$instance – general information about the
instance
• Some of those views are available when the
database is closed
Example scenario
• The database cannot start, error message is that
file number 4 is corrupt.
• Recovery:
– STARTUP MOUNT
– SELECT name FROM v$datafile WHERE file# = 4
– fix the problem with the file, e.g. restore it from
backup
– recover the database
– ALTER DATABASE OPEN