Download Lecture 3

3
Managing an Oracle Instance
Objectives
• Setting up operating system and
password file authentication
• Creating the parameter file
• Starting up an instance and opening the
database
• Closing a database and shutting down
the instance
• Getting and setting parameter values
• Managing sessions
• Monitoring ALERT and trace files
Overview
Instance
SGA
User
process
Shared pool
Server
process
PGA
ALERT
file
Control
files
Parameter
file
Password
file
Data files
Redo log
files
Database Administrator Users
The two database administrator users
SYS and SYSTEM are:
• Automatically created
• Granted the DBA role
User SYS and SYSTEM
SYS
SYSTEM
• Password:
• Password:
change_on_install
• Owner of the
database data
dictionary
manager
• Owner of additional
internal tables used
by Oracle tools
Authentication Methods
Remote database
administration
Do you
have a secure
connection?
No
Yes
Local database
administration
Do you want
to use OS
authentication?
Yes
Use OS
authentication
No
Use a
password file
Operating System
Authentication
• Set up the user to be authenticated by
the operating system.
• Set REMOTE_LOGIN_PASSWORDFILE
(in init.ora) to NONE.
• Use the following commands to connect
to a database:
CONNECT / AS SYSDBA
CONNECT / AS SYSOPER
Using Password File
Authentication
• Create the password file using the
password utility:
$orapwd file=$ORACLE_HOME/dbs/orapwU15\
password=admin entries=5
• Set REMOTE_LOGIN_PASSWORDFILE
(init.ora) to EXCLUSIVE or SHARED
• Use the following command to connect
to a database:
CONNECT INTERNAL/ADMIN
Changing the Internal Password
• Use the password utility on NT and UNIX
to delete and create the password file.
or
• Use the ORADIM80 utility on NT to delete
and create a new password file.
Uses of Parameters
•
•init<SID>.ora
•Size the SGA
•Set database and instance defaults
•Set user or process limits
•Define various physical attributes (e.g.,
database block size)
•Specify control files, datafiles, redo log files,
etc.
The Initialization Parameter File
Instance
SGA
Shared pool
Library
cache
Database
buffer
cache
Redo log
buffer
SMON DBWR PMON CKPT
Data
dictionary
cache
LGWR ARCH
initU15.ora
SVRMGR> CONNECT / AS SYSDBA
SVRMGR> STARTUP PFILE=/DISK1/initU15.ora
Parameter File Example
# Initialization Parameter File: initU15.ora
db_name
= U15
control_files
= (/DISK1/control01.con,
/DISK2/control02.con)
db_block_size
= 8192
db_block_buffers
= 2000
shared_pool_size
= 30000000
log_buffer
= 64K
processes
= 50
db_files
= 100
log_files
= 10
max_dump_file_size
= 10240
background_dump_dest = (/home/disk3/user15/BDUMP)
user_dump_dest
= (/home/disk3/user15/UDUMP)
core_dump_dest
= (/home/disk3/user15/CDUMP)
rollback_segments
= (r01,r02,r03,r04,r05,r06,r07,r08)
...
Startup and Shutdown in Stages
OPEN
MOUNT
All files opened as
described by the
control file for this
instance.
Control file
opened for this
instance.
NOMOUNT
Instance
started.
SHUTDOWN
Startup and Shutdown (cont.)
Starting an instance includes:
• Reading the parameter file
• Allocating the SGA
• Starting the background processes
• Opening the ALERT and trace files
STARTUP Command
Start up the instance, and
open the database.
STARTUP PFILE=/DISK1/initU15.ora
STARTUP [FORCE][RESTRICT][PFILE = filename]
[OPEN [RECOVER][database]
| MOUNT
| NOMOUNT]
STARTUP Command
OPEN: enables users to access the database
MOUNT: mounts the database for certain
activities but does not allow user access to db
NOMOUNT: creates SGA + bg processes; no
access to database
FORCE: aborts the running instance before
performing a normal startup
RESTRICT: restricted access
RECOVER: begins media recovery
ALTER DATABASE Command
•Change state of the database from NOMOUNT to
MOUNT
• ALTER DATABASE database MOUNT
•Open the database as a read-only database
•ALTER DATABASE database OPEN READ
ONLY
Opening a Database in ReadOnly Mode
•Any database can be opened as a read-only
database
•A read-only database can be used to:
•Execute queries
•Execute disk sorts
•Take datafiles offline and online
•Perform recovery of offline data files
Shutdown Options
Shutdown Mode
A
I
T
N
Allow new connections
X
X
X
X
Wait until current sessions end
X
X
X
O
Wait until current transactions end
X
X
O
O
Force a checkpoint and close files
X
O
O
O
Shutdown mode:
A Abort
I Immediate
T Transactional
N Normal
NO
YES
Shutdown Time
4
3
2
1
Normal
Time
Transactional
Immediate
Abort
Oracle Memory and Background
Processes: Connecting to a Shared Server
Red lines trace
the path
between the
client and the
instance
Oracle Memory and Background
Processes: Connecting to a Dedicated Server
Red lines trace
the path
between the
client and the
instance
Oracle Memory : PGA & SGA
The PGA has
private areas
for each
application
The SGA is
allocated
when the
instance
starts up
Oracle Memory : SGA Components
The buffer
cache stores
data blocks
read from the
datafiles
The shared
pool stores
parsed SQL
commands
for possible
reuse
Oracle Memory: SGA Components
The cursor
pool is
optional and
provides extra
memory for
program
cursors
The redo log
buffer stores
all changes to
data before
the changes
are written to
the datafiles
The large pool
is optional and
adds more
memory for
better
response time
Background Processes: PMON & SMON
PMON (Process
Monitor) cleans
up remaining
resources
after the server
and user
processes end
SMON (System
Monitor) handles
recovery if
needed, cleans
up old temporary
tables, and
restores space
Background Processes: DBWn & CKPT
DBWn (Database
Writer) writes
modified buffers
to the datafiles
CKPT
(Checkpoint
Process) signals
the DBWn
process and
assigns SCN
Background Processes: ARCn & LGWR
ARCn (Archiver)
copies redo log
files to archive
log files
LGWR (Log
Writer) writes
redo log buffers
to the redo log
files
Background Processes: RECO & LMS
RECO (Recoverer
Process) fixes
errors if changes
across distributed
databases fail
LMS (Lock
Manager Service)
handles updates
that affect data in
multiple clustered
databases
Dynamic Performance Views
• Maintained by the Oracle Server
and continuously updated
• Contain data on disk and memory
structures
• Contain data that is useful for
performance tuning
• Have public synonyms with the
prefix V$
Accessing Dynamic
Performance Views
OPEN
Data dictionary
MOUNT
NOMOUNT
SHUTDOWN
Dynamic
performance
views reading
data from disk
Dynamic
performance
views reading
from memory
Example
SGA
Control file
V$PARAMETER
V$SGA
V$OPTION
V$PROCESS
V$SESSION
V$VERSION
V$INSTANCE
V$THREAD
V$CONTROLFILE
V$DATABASE
V$DATAFILE
V$DATAFILE_HEADER
V$LOGFILE
Displaying Current
Parameter Values
• Use the Server Manager command:
SHOW PARAMETER control
• Query the dynamic performance view
V$PARAMETER:
SELECT name FROM v$parameter
WHERE name LIKE ‘%control%’;
Dynamic Initialization Parameters
Some initialization parameters can be
modified while an instance is running.
ALTER SESSION SET SQL_TRACE=true;
ALTER SYSTEM SET TIMED_STATISTICS=true;
ALTER SYSTEM SET SORT_AREA_SIZE=131072
DEFERRED;
Enable and Disable
Restricted Session
• Use the STARTUP command to
restrict access to a database:
STARTUP RESTRICT
• Use the ALTER SYSTEM command to
place an instance in restricted mode:
ALTER SYSTEM ENABLE RESTRICTED
SESSION;
Terminating Sessions
1. Identify which session to terminate
with the dynamic performance view
V$SESSION:
SELECT sid, serial# FROM v$session
WHERE username=‘SCOTT’;
2. Execute the ALTER SYSTEM command:
ALTER SYSTEM KILL SESSION ‘7,15’;
Trace Files
• Trace files can be written by server
and background processes.
• Oracle dumps information about errors
in trace files.
• The ALERT file consists of a
chronological log of messages and
errors.
• Server process tracing can be enabled
or disabled by:
– An ALTER SESSION command
– The parameter SQL_TRACE
Controlling the Trace File
Instance
SGA
User
process
Shared pool
Server
process
ALERT file
USER_DUMP_DEST
BACKGROUND_DUMP_DEST
Guidelines
Check the ALERT file periodically to:
• Detect internal errors (ORA-600)
and block corruption errors
• Monitor database operations
• View the nondefault initialization
parameter
Summary
• Creating the parameter file
• Starting up and shutting down an
instance
• Understanding the use of dynamic
performance views
• Manage sessions
• Describing the use of trace files