Download DBA625 Covered so far

Material to be Covered During DBA625 Lectures, WINTER 2014
Text Book: Oracle 11g Notes -- DBA ( official Oracle Notes)
Week 1:
Intro:
INTRODUCTION incl. Course Objectives
Lesson 1: ORACLE DATABASE ARCHITECTURE
Commands/Content:
Course Overview and Course Objectives
History of Oracle Evolution , Years and Versions
Oracle Products and Services
Interacting with an Oracle Database – Steps
Oracle Database Server Structure
What is an Instance and what is a Database --> together they form a Database Server
Instance is made of SGA (Shared - System Global Area) and several Background Processes
Database is made of bunch of files and the Database Core contains Control files, Redo Log files and
Data files (all are in binary format)
All SGA Regions: 1. SHARED_POOL
-- Library Cache (holds most recently executed SQL and PL/SQL statements, their parsed versions
and their Execution plans
-- Dictionary (Row) Cache (holds information about Data Dictionary Objects and User's Privileges)
-- New
TO 11g are SQL and PL/SQL Result Caches
Both caches behave by the LRU algorithm, so that data blocks are aged out if not being used very
often
2. DATA BUFFER CACHE (DBC)
-- holds recent Data Blocks that contain rows being processed by users' SQL statements
-- 3 states of buffers --> a) Clean) b) Dirty c) Pinned (which will become clean or dirty)
-- behaves according to the LRU algorithm as well
3. LOG BUFFER CACHE (LBC)
-- holds only Data Blocks that are “dirty” – blocks that contain either DML or DDL modifications
by users
-- behaves in a circular manner, so that data blocks are aged out in the order they arrived
4. LARGE POOL (optional region)
-- holds information about Shared Server, I/O related tasks and RMAN related topics for
Backup/Restore operations (only if used)
5. JAVA POOL (optional region)
-- stores information for JVM and Java related applications (only if used)
6. STREAMS POOL (optional region)
-- holds information about product ORACLE STREAMS (if being used0
Important SGA parameters are:
1. DB_BLOCK_SIZE(static, lifetime) -- 2K, 4K, 8K (default), 16K,32K --> can NOT be
changed ever
2.. SGA_MAX_SIZE (static) -- in hundreds of M till several GB, this is MAX value for SGA
that can be used (if specified)
3. SGA_TARGET (dynamic) -- less or equal to SGA_MAX_SIZE , if non-zero value then
considers values for parameters 6,7,9,10 as MINIMAL ones (if specified) and
it means that DBA is going for ASMM (Auto Shared Memory
Management) Feature
4. MEMORY_MAX_SIZE (dynamic) -- if specified, this is MAX amount of memory for BOTH
SGA components and PGA part
5.MEMORY_TARGET (dynamic) -- less or equal to MEMORY_MAX_SIZE, Server takes
care of BOTH SGA components and PGA with non-zero value here
-- Parameters 4 and 5 are new to 11g.
6.. SHARED_POOL_SIZE (dynamic) -- at least 64MB till several GB
7. DB_CACHE_SIZE (dynamic) -- at least 32MB till several GB
8. LOG_BUFFER (static) -- from 2.7M till several MB
9. LARGE_POOL_SIZE (dynamic) -- from 4MB till several hundreds MB, might be set to 0
initially at startup
10. JAVA_POOL_SIZE (dynamic) -- from 4MB till several hundreds MB, might be set to 0
initially at startup
Week 2:
Lesson 1: ORACLE ARCHITECTURAL COMPONENTS continued
Lesson 2: PREPARING THE DATABASE ENVIRONMENT (on LINUX) incl. DBA Tasks and
Duties
Commands/Content:
Process architecture – User and Database (it may be Server and Background) processes
Two types of Server Process – Dedicated (one for each User) and Shared (may serve many Users and
needs one or more Dispatcher processes)
Important Background Processes -- SMON, PMON, LGWR, DBW0, CKPT, ARC0 (optional),
MMON, MMAN, CJQ0, Jnnn
Task of DBW0 is to flush off all “dirty” buffers from DBC to Data Files on disk. Here is
Checkpoint a crucial criteria or when it can not find Free buffer after scanning a certain number of
buffers.
Note: "Dirty buffers" flush off by DBWR to Data Files may happen anytime before/after the Commit
and it may happen that some NOT committed buffers finish on Disk
Task of LGWR is to flush off SEQUENTIALLY all buffers from LBC to Redo Log Files on disk.
Here is Commit a crucial criteria or
when Log buffer one third full, or every 3 000 mili-seconds or
always before Database Writer writes.
SMON is performing at the STARTUP following 3 actions (if the Instance Crash happened)
1. ROLL FORWARD -- moving committed transactions from Redo Logs to Data Files
2. OPENS DATABASE -- only partially (the Database part not affected with step 3)
3. ROLLBACK -- all NOT committed transactions that were placed in Data Files (by using Undo
Segments)
Note: It might happen (although rarely) that some NOT committed transactions finish on
Disk (in Data Files)
PMON is performing cleanup after User process has failed, which involves 3 steps:
1. Releasing all Locks that were imposed by that User session
2. Rollback of Not committed transactions by that User session
3. Releasing all Resources (memory and disk) that were held by that User session
Oracle Database Files -- CONTROL FILE (min 1), REDO LOG FILES (min 2) and DATA FILES
(min 3),
Other Key Files -- Password File, Alert Log File alert_SID.log, Trace Files (for Background and
Server processes)
Server Parameter file spfileSID.ora and Initial Parameter File initSID.ora
Database Storage Architecture  Tablespace, Segment, Extent and Data Block vs. Data Files and OS
Blocks
SYSTEM and SYSAUX tablespaces as mandatory ones (SYSTEM must be On-Line always). The
third mandatory tablespace is UNDOTBSP.
Tasks and Duties of a DBA.  Ten tasks incl. Performance Tuning.
Database Administration Tools -ORACLE UNIVERSAL INSTALLER, DATABASE CONFIGURATION ASSISTANT, EM,
SQL*PLUS, SQL*LOADER, EXPORT/IMPORT etc.
System Requirements – Kernel parameters, Memory and Disk space
Planning Database File Locations, What is OFA (Optimal Flexible Architecture)
Important Environment Variables like ORACLE_BASE, ORACLE_HOME, ORACLE_SID, HOME,
PATH then
where to look for 'admin', 'oradata', 'diag', 'trace', 'pfile' etc. subdirectories
How to set the Environment Variable with export VAR=value and how to check that value with echo
$VAR
Oracle Universal Installer --> Installing 11g Enterprise Database on Linux --> Steps and Options
(incl. Advanced options)
Planning the Database (Capacity Planning)
Week 3:
Lesson3: CREATING AN ORACLE DATABASE
Lesson 4: MANAGING the ORACLE INSTANCE
Commands/Content:
Creating a New Database -- GUI by using the Database Configuration Assistant (DBCA) or by using
Scripts
Configuring a Starter Database by using DBCA, Steps and Options
Other features of DBCA  Delete Database, Configure Database Template, Manage Templates and
Configure ASM (Automatic Storage Management)
Default Administrator's Accounts/Passwords --- Three types with the different power descending:
SYS/ORACLE AS SYSDBA, --> Password may be ORACLE as well
SYS/ORACLE AS SYSOPER --> Password may be ORACLE as well
SYSTEM
--> Password may be ORACLE as well
DBSNMP
--> Password may be ORACLE as well
Two basic Authentication Methods -- OPERATING SYSTEM and PASSWORD FILE
Value of the parameter REMOTE_LOGIN_PASSWORDFILE to either
NONE for OS authentication > CONNECT / AS SYSDBA
EXCLUSIVE for the Single Instance and Oracle Password option and
> CONNECT SYS/ORACLE AS SYSDBA
SHARED for the RAC ( FORMER OPS) option with Oracle Password
What is Listener (Process) and how to ADD one by using Oracle Net Configuration Assistant
(NETCA)
How to START and STOP Listener in Linux with:
$ lsnrctl start | stop
How to START and STOP Database Control (EM) in Linux with:
$ emctl start | stop dbconsole
What is ENTERPRISE MANAGER (EM) and how to invoke it with
https://hostname:PORT/em
Home Page of EM
What is SQL*PLUS and how to use the COMMAND LINE MODE
What is the Initialization Parameter File initSID.ora and what are the crucial parameters and their
possible values:
Db_name, Instance_name, Db_block_size, Db_cache_size, Shared_pool_size, Log_buffer,
Control_files, Compatible,
Processes, Undo_management, Memory_Target, SGA_Target, Memory_Max_Target,
SGA_Max_Size, PGA_Aggregate_Target
PFILE (ASCII text/static/manual editing) vs. SPFILE (binary/dynamic-persistent/modified through
command line)
Using SHOW PARAMETER string to see the names and values for all parameters containing string or
going for data dictionary view V$PARAMETER and V$SPPARAMETER
Two ways to Set (change) a Database Initialization Parameter -STATIC (editing the entry in the parameter file PFILE , shutting down and restarting the
instance) or
DYNAMIC (by either changing it for a SESSION or SYSTEM or SYSTEM Delayed option) by
using:
> ALTER { SESSION| SYSTEM} SET parameter=value [DEFERRED]
How to MODIFY dynamically values in SPFILE by specifying SCOPE, where default value for PFILE
is Memory and for SPFILE is Both
> ALTER SYSTEM SET paramater=value [SCOPE = {MEMORY| SPFILE| BOTH}]
How to see content of the SPFILE (using 'more' or Wordpad) , but it can NOT be edited.
Three Database Startup Stages -- NOMOUNT, MOUNT and OPEN (default), also possible
RESTRICT mode upon startup for DBA’s only
Changing the stage with ALTER DATABASE {MOUNT | OPEN}or
ALTER DATABASE OPEN READ {WRITE | ONLY}
Four Database Shutdown Modes -- NORMAL (default for SQL), TRANSACTIONAL, IMMEDIATE
(default in EM) and ABORT
What activity is NOT allowed in each of these four stages
How to Enable/Disable a Restricted Session while the Instance is running, but only for new users
with:
> ALTER SYSTEM { ENABLE| DISABLE} RESTRICTED SESSION;
What is an Alert Log File -- Database diary or journal and its default directory
$ORACLE_BASE/diag/rdbms/Db_Name/SID/alert
How to view Alert Log file dynamically with tail -f alert_SID.log
Two types of Trace Files -- for BACKGROUND PROCESSES, they reside in the same directory as
Alert Log file
and SERVER PROCESSES, they reside in default directory
ORACLE_BASE/diag/rdbms/Db_Name/SID/trace
What are Dynamic Performance Views – dynamic info about operation/performance of the instance,
owned by SYS user, all names stored in the V$FIXED_TABLE
and which ones can be accessed at NOMOUNT, MOUNT or OPEN stage
like V$INSTANCE, V$PARAMETER, V$SGA, V$CONTROLFILE, V$DATABASE, V$LOG,
V$LOGFILE, V$DATAFILE, DBA_viewname etc.
Data Dictionary Views and Categories ( USER_name ALL_name and DBA_name )
Week 4:
Lesson 6: MANAGING DATABASE STORAGE STRUCTURES – about CREATE TABLESPACE
(Permanent) and ALTER TABLESPACE/DATABASE
Commands/Content:
Database Storage Hierarchy -- Logical vs. Physical Storage Model
Logical components are: Database, Tablespaces, Segments, Extents and Database Blocks
Physical components are: Datafiles and Operating System Blocks
Two basic Types of Tablespaces are:
Mandatory -- SYSTEM, SYSAUX, UNDO and Optional - USERS, TEMP, INDEX, TOOLS,
EXAMPLES etc.
How to add a new Tablespace with default options (PERMANENT, ONLINE, LOGGING, READ
WRITE)
and default EXTENT MANAGEMENT mode --> LOCAL with:
CREATE TABLESPACE tbsp_name
DATAFILE '/path/filename' SIZE { 100M | n {K | M }}
-- where 'path' means the Full
Unix Path to the directory
[ AUTOEXTEND { OFF | ON [NEXT n{K|M}] [MAXSIZE {UNLIMITED | n{K|M}}] } ]
[ EXTENT MANAGEMENT LOCAL [{ AUTOALLOCATE | UNIFORM [SIZE {1M |
n{K|M}}]}] ]
[ SEGMENT SPACE MANAGEMENT { AUTO | MANUAL}] ;
How to choose Dictionary Management Mode instead of Local one by using Default Storage clause
that allows for customizing the size of all extents with: :
EXTENT MANAGEMENT DICTIONARY [MINIMUM EXTENT n{K|M}]
[DEFAULT STORAGE (INITIAL n{K|M} NEXT n{K|M} MINEXTENTS n MAXEXTENTS n
PCTINCREASE n)]
Local Mode means that Free Extents are managed through a Bitmap (bunch of 1 and 0), each bit
represents a Group of Blocks
Dictionary Mode means that Free Extents are managed through a Data Dictionary (slower and may
lead to the Fragmentation)
Default Extent Management Submode for LOCAL is AUTOALLOCATE --> Server will decide about
the Extent Size (MULTIPLES of 64K) and
we will NOT know what will be that value; If we go for UNIFORM without specifying SIZE --> it will
be 1M always
How to change (modify) Default Tablespace options with:
ALTER TABLESPACE tbsp_name NEWOPTION ;
where NewOption may be TEMPORARY, OFFLINE, NOLOGGING, READ ONLY
Three Methods to ADD space or to CHANGEsize of a Tablespace:
1) Add a new datafile to a Tablespace with:
ALTER TABLESPACE tbsp_name
ADD DATAFILE 'path' SIZE { 100M | n{K|M}} [autoextend_option]
2) Manually resize (desize as well) an existing datafile with:
ALTER DATABASE DATAFILE 'path/filename' RESIZE n{K|M}
3) TURN ON the automatic extent increasing for an existing datafile with:
ALTER DATABASE DATAFILE 'path/filename'
AUTOEXTEND ON [NEXT n{K|M} [MAXSIZE {UNLIMITED | n{K|M}}]]
How to move a system datafile or any datafile with active Undo segments with:
SHUTDOWN,
OS move with mv command
STARTUP MOUNT
ALTER DATABASE RENAME FILE 'old_path' TO 'new_path' and
ALTER DATABASE OPEN
How to move any ordinary (non-system and non-undo) datafile with:
ALTER TABLESPACE tbsp_name OFFLINE,
OS move with mv command
ALTER TABLESPACE RENAME DATAFILE 'old_path' TO 'new_path' and
ALTER TABLESPACE tbsp_name ONLINE
How to drop an existing Tablespace and all Datafiles there with just one command:
DROP TABLESPACE tbsp_name [INCLUDING CONTENTS AND DATAFILES]
Note: OS removal of all files associated with this tablespace is NOT needed anymore, becuse of
AND DATAFILES option
It is possible to drop a SINGLE DATAFILE in SQL, but you should NOT use it, because the
mistake here is very costly
(you have to go for a WHOLE TABLESPACE or ignore the not-needed datafiles)
Important Data Dictionary views are:
V$TABLESPACE, V$DATAFILE (it shows the current and original file size) and can be observed
in the MOUNT or OPEN stage and
DBA_TABLESPACES, DBA_DATA_FILES (it shows all 3 Auto-extent components) and can be
observed only in the OPEN stage
Week 5:
Lesson 6: MANAGING DATABASE STORAGE STRUCTURES -- about TEMPORARY
TABLESPACES
Lesson 14: BACKUP AND RECOVERY CONCEPTS  only the part about Instance Recovery and
Checkpoints, Logfiles and Controlfiles
Lesson 10: MANAGING UNDO DATA
Commands/Content:
Temporary Tablespaces are used strictly for SORT operations (as with ORDER BY, GROUP BY,
DISTINCT etc.)
and they can NOT contain Permanent objects (like Tables, Indexes, Clusters etc)
How to add a new Temporary Tablespace with the
CREATE TEMPORARY TABLESPACE tbsp_name
TEMPFILE 'path' SIZE n{K|M}
[EXTENT MANAGEMENT {LOCAL UNIFORM [SIZE { 1M | n{K|M}}] | DICTIONARY}]
Default Management Mode is LOCAL and UNIFORM of 1M, and you can NOT use
AUTOALLOCATE option for Extent Mgmt.
Tempfiles are always at NOLOGGING mode and they can NOT be made READ ONLY
Default Temporary Tablespace may be declared when Database is created or later by using:
ALTER DATABASE DEFAULT TEMPORARY TABLESPACE tbsp_name;
Default Temporary Tablespace can NOT be dropped, nor taken offline, nor altered to a permanent one
Important Data Dictionary views are:
V$TEMPFILE, DBA_TEMP_FILES,
What is NOT POSSIBLE in Oracle11g:
1. To create any Tablespace with the DICTIONARY option if System Tablespace is created as
LOCAL
2. To change the Submode for Local option from AUTOALLOCATE to UNIFORM and vice
versa
3. To change the size of the Extents for an UNIFORM Tablespace
4. To create a TEMPORARY Tablespace with the AUTOALLOCATE option --> it has to be
UNIFORM (default size is 1M)
5. To create an UNDO Tablespace as UNIFORM --> it has to be AUTOALLOCATE option
Usage of the Control File -- Small binary file, Linked only to the one Database, Mandatory (should be
multiplexed)
Content of the Control File -Database name, Time stamp of the Database creation, Names and Locations of all core Database
files,
Tablespace info, Log history, Location and Status of archived log files, Current Log Sequence
Number (LSN)
Current Checkpoint Number and Last Commited Transaction Number (System Change Number -SCN)
Multiplexing the Control File -- Steps
Add new name (s) to the parameter CONTROL_FILES in the PFILE (initSID.ora file)
Shutdown,
Copy (Move) the file (s) to another location(s) in Linux
Startup with PFILE
Important Data Dictionary view is V$CONTROLFILE
Purpose of Redo Log files --To enable Instance Recovery and with Archived Log files to enable Media (Disk)/Human
Errors Recovery
Redo Log Groups and Members, Minimum is to have two groups and one member
What is the Current Log Group and Log Sequence Number
What triggers LGWR to write into the current log group (most important is COMMIT request)
How to achieve a Log Switch -Naturally by file being filled and Manually with > ALTER SYSTEM SWITCH LOGFILE
What happens during a Checkpoint – all datafile headers are in sync with controlfile info about the
latest SCN and its Checkpoint Position
What types of Checkpoints do exist:
a) FULL -- caused by clean SHUTDOWN or by DBA manual command > ALTER SYSTEM
CHECKPOINT
b) PARTIAL – caused by placing Tablespace or Datafile OFFLINE
c) INCREMENTAL -- Influenced by setting just ONE parameter, so that DBW0 becomes more
active and Checkpoint Position
in the Redo Log File (the position where SMON would begin an Instance Recovery)
advances with better pace
(ensuring that all transactions with the SCN before that position are saved in Datafiles on
disk)
FAST_START_MTTR_TARGET (in seconds, Default 0 -- meaning Incremental
Checkpointing is turned off)
Important dynamic views V$LOG and V$LOGFILE and different values of column STATUS in
these views
How to add a new Log Group or a new Log Member with:
ALTER DATABASE ADD LOGFILE { 'path' SIZE n{K|M} | MEMBER 'path' TO GROUP n}
How to move (relocate) a Redo Log File with just two steps (SHUTDOWN is not needed anymore):
1. OS move witth mv command, then using
2. ALTER DATABASE RENAME FILE 'old_path' TO 'new_path'
How to drop (remove) an existing Log Group or Log Member with
1. ALTER DATABASE DROP LOGFILE {GROUP n | MEMBER 'path'}and then
2. OS removal with rm command
Undo Data is a COPY of original, pre-modified data (by DML statements) captured for EVERY
transaction
It supports 4 different things:
1) ROLLBACK (Undo) operations by developers and users
2) Read Consistent Queries by users who only want to read data being modified (by someone
else)
3) Instance Recovery by SMON -- SECOND part called SYSTEM ROLLBACK (performed
just after Roll Forward)
4) FLASHBACK Features – Query, Transaction and Table (but NOT for Flashback Database)
Each Transaction uses ONLY ONE Undo Segment, while several Transactions may share the same
segment
Undo Segments are stored in the UNDO TABLESPACE, and the preferred type of Undo Management
is AUTOMATIC (and default one)only one such Tablespace may be active at the time
Parameter UNDO_MANAGEMENT may be AUTO (Default) or MANUAL, and parameter
UNDO_TABLESPACE is by Default UNDOTBS1
In AUTO management system assigns 10 Undo Segments of the same size to the created Tablespace
and handles usage of these segments automatically
You may create several Undo Tablespaces with > CREATE UNDO TABLESPACE tbspaname
DATAFILE ‘/path/filename’ SIZE {100M | n {K|M}}
and also you may AUTOEXTEND its Datafile, but the EXTENT MANAGEMENT must be
system determined (AUTOALLOCATE)
Only ONE Undo Tablespace may be active at the time, while the other ones are in dormant state. You
declare it active with the following syntax:
> ALTER SYSTEM SET undo_tablespace = undonew;
Parameter UNDO_RETENTION (specified in Seconds, Default 900) determines how long (at least)
already committed transaction is to be retained in Undo Segment
It is enabled for the following circumstances by system (otherwise, this parameter is ignored):
1) The UNDO Datafile has the AUTOEXTENSION set to ON -- it keeps committed data for at
least the Retention Interval
2) The UNDO Tablespace has GUARANTEED retention -- it keeps committed data for at least
the Retention Interval
3) When modifying LOB datatypes
Undo Data is divided into 3 categories:
1) Uncommitted (ACTIVE) -- supports current transaction. It is NEVER overwritten
2) Committed (UNEXPIRED) -- transaction has ended, but it is still within the Retention
Interval. If NOGUARANTEE is enabled, the undo data will be retained (if possible),
without causing a new transaction to fail, because of the lack
of the disk space. Otherwise (for GUARANTEE option) will be always honored.
3) Committed (EXPIRED) -- transaction has ended, but it is past (beyond) the Retention
Interval. It will be overwritten firstly to make a space for a new transaction.
How to change Guarantee option for an Undo Tablespace with:
> ALTER TABLESPACE undotbsp {GUARANTEE | NOGUARANTEE} ;
How to use UNDO ADVISOR in EM to get an estimate for the Undo Tablespace SIZE to satisfy
given RETENTION INTERVAL
Week 6:
Lesson9: MANAGING DATA and CONCURRENCY  just the part about RESOLVING LOCKS
Lesson 5: CONFIGURING ORACLE NET ENVIRONMENT
Commands/Content:
Locks prevent multiple sessions from changing the same piece of data (row, rows or table) at the
same time. They are obtained at the lowest possible level (row) by server.
Default Locking Mechanism in Oracle Database has 4 important features that enable the highest
possible level of Data Concurrency:
1) AUTO Queue Management by Server – it keeps track of the following:
a) What Sessions are waiting for locks
b) Order in which these Sessions are waiting
c) Requested Lock Mode
2) Row Exclusive Level locks for DML statements
3) NO locks required for SELECT statement (except when FOR UPDATE option is used)
4) Locks are held until transaction ends (Commit or Rollback) and then are automatically
released
You can use the following syntax to impose MANUAL LOCKING mode for Tables (NOT
recommended by Oracle)
> LOCK TABLE [owner.]tablename IN {ROW SHARE | ROW EXCLUSIVE | SHARE | SHARE
ROW EXCLUSIVE | EXCLUSIVE} MODE [{WAIT | NOWAIT |WAIT n}];
ROW EXCLUSIVE locks are automatically obtained when performing DML statements
-- they allow multiple readers and only one writer
SHARE locks are automatically obtained when creating an Index on a table -- they allow
multiple readers and NO Updates
EXCLUSIVE lock is obtained when Dropping a table -- they allow multiple readers and
nothing else
Most important causes of Lock Conflicts that cause sessions to WAIT to execute their DML/DDL
statements are:
1) Users do NOT commit their changes promptly
2) Long running transactions with Commit only at the end
3) Manual Locking by developers who are not trained well or who do not understand how
Locking Mechanism (imposed by Server) works
You can detect Lock Conflicts by using EM Home Database Page  Performance  Additional
Monitoring Links Blocking Sessions OR
by checking V$LOCK and V$SESSION Performance Views
To resolve Lock Conflict either Force User who holds the Blocking Session to Commit (Rollback)
OR
Terminate (kill) that session with
> ALTER SYSTEM KILL SESSION
‘SID, SERIAL#’ IMMEDIATE;
Deadlocks happen if two sessions are modifying (in the opposite order) two same rows at the same
time, without committing the first change
Oracle Server will detect Deadlock automatically and undo the second change by the first session, that
will receive Deadlock Error ORA-060,
and then this session needs to commit (rollback) its first change, while the Second session will
experience just a bit of waiting without any error message
The material related to Oracle Net Services (Chapter 5) should be mastered over
Session8 document on the Work Page
Week 7:
SAMPLE TEST / Assignment One is due
Lesson 8: MANAGING SCHEMA OBJECTS – TABLES
Commands/Content:
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Note: If Tablespace to hold that table was created with SEGMENT SPACE MANAGEMENT AUTO
(default), then PCTUSED and FREELISTS are ignored
How to change extent values (all of them may be modified except INITIAL) or space block parameter
values (all of them may be modified except FREELISTS) with:
ALTER TABLE [user.]table_name
STORAGE (NEXT n{K|M} MINEXTENTS n MAXEXTENTS n PCTINCREASE n)
PCTFREE n PCTUSED n INITRANS n MAXTRANS n ;
Week 8:
MID-TERM TEST
Lesson 8: MANAGING SCHEMA OBJECTS – TABLES cont.
Lesson 8: MANAGING SCHEMA OBJECTS -- INDEXES
Commands/Content:
How to manually allocate a new extent for a table with:
ALTER TABLE [user.]table_name ALLOCATE EXTENT [SIZE n{K|M}] [DATAFILE 'path'];
How to move a non-partitioned table into a different tablespace with:
ALTER TABLE [user.]table_name MOVE TABLESPACE tbsp_name; this command might
be used also for changing parameters like INITIAL (extent) and FREELISTS, that previously
could
have not been changed OR for reorganizing the free space situation in tables' extents with just:
ALTER TABLE [user.]table_name MOVE ;
How to truncate an existing table, so that table structure, all constraints, indexes and triggers are not
affected and the space is released or not with:
TRUNCATE TABLE [user.]table_name [ {DROP | REUSE} STORAGE];
How to drop an existing table with or without data and with possible FK reference by using:
DROP TABLE [user.]table_name [CASCADE CONSTRAINTS];
Important dynamic views are: DBA_TABLES, DBA_TAB_COLUMNS
Classification of Indexes:
LOGICAL (Single or Composite ; also Unique or Non-unique; also Regular or Function based)
PHYSICAL (B-tree Normal or Reverse and Bitmap; also Partitioned or Non-partitioned)
Structure of the B-tree Index Leaf Entry:
1. Entry Header that stores # of columns and locking info
2. Key column length and value pairs -- if the Index is composite (otherwise, it is just one length
and one value)
3. ROWID -- it points to a mother table's row with that key value.
Structure of the Bitmap Index Entry:
1. Entry Header that stores # of columns and locking info
2. Key column length and distinct value
3. Start Rowid and End Rowid to indicate the range of rows for this table (Only Restricted
Rowid is used)
4. Long binary string where the bit is set to 1 if the corresponding row contains that distinct key
Comparison between B-tree and Bitmap Indexes -Columns with lots of distinct values in the OLTP environment should use B-tree and
Columns with few distinct values in DSS or Data Warehousing should use Bitmap Indexes
How to create an Index with default options (LOGGING, NOCOMPRESS, SORT) and customized
extent and space block parameters:
CREATE { ____ | UNIQUE | BITMAP } INDEX [user.]index_name
ON [user.]table_name (column1 [, column2, ...]) [REVERSE]
TABLESPACE tbsp_name
STORAGE (INITIAL n{K|M} NEXT n{K|M} MINEXTENTS n MAXEXTENTS n PCTINCREASE n)
PCTFREE {10 | n } INITRANS {2 | n } MAXTRANS { 255 | n };
Guidelines on how and when to create an Index -- avoid them if DML operations are frequent,
PCTFREE works differently than for tables -- it is used for future inserts and should be set to a
higher value, while PCTUSED can not be set, NOLOGGING may be used for large indexes.
How to rebuild an Index with:
ALTER INDEX [user.]index_name REBUILD {OFFLINE | ONLINE}
[TABLESPACE tbsp_name] [{REVERSE | NOREVERSE}] [{LOGGING | NOLOGGING}]
[PCTFREE];
Note: It is possible to rebuild an Index and NOT to lock a whole table (which will allow concurrent
DML operations) by using the ONLINE option (OFFLINE is default)
Main reasons for doing a Rebuild are:
1. Changing the tablespace or PCTFREE,
2. Switching from Normal to Reverse mode and vice versa (only for B-tree indexes) or
3. Just to get rid of deleted leaf entries and to use space better (defragment the Index)
How to drop an existing index by using:
DROP INDEX [user.]index_name ;
Main reasons for dropping an index are:
1. It is no longer needed or used only periodically
2. It is Invalid
3. Before huge bulk loads (inserts) to speed up this process and re-create index later
Important dynamic views are DBA_INDEXES, DBA_IND_COLUMNS
Week 9:
Lesson 8: MANAGING SCHEMA OBJECTS -- CONSTRAINTS
Commands/Content:
Data integrity Methods -- Database Triggers, Application Code and Integrity Constraints
Types of Constraints -- PRIMARY KEY, UNIQUE, FOREIGN KEY, CHECK and NOT NULL (as a
special CHECK type)
Four possible States when enabling/disabling a constraint:
Disable Novalidate -- constraint is TURNED OFF i.e NOT enforced at all (default state, if
DISABLE option)
Disable Validate -- the Table becomes READ ONLY when any of its constraints gets this state i.e
NO DML operation will be allowed for this Table (only Select statements)
Enable Novalidate -- new (future) Insert/Update statements will be checked against constraint
violation,
but existing rows in the Table will NOT be checked, it will NOT lock the table
Enable Validate -- both existing (old) and future (new) rows WILL BE checked against constraint
violation,
i.e when this state becomes active NO false rows can exist in the Table.
This is default state for the constraint state (if nothing specified), it will lock the table if going
from Disable state
Deffering a constraint checking may have two Modes:
Not Deferrable (Immediate) -- this mode will enforce the constraint at the end of EACH DML
statement,
i.e each Line in the DML Procedure will be inspected against the constraint violation
(Default mode)
Deferrable -- this mode might POSTPONE (DEFER) constraint checking till COMMIT time and
must be
specified when the constraint is CREATED. This mode has two Options:
Initially Immediate (SubDefault option) -- still the constraint will be checked as the
Immediate one,
but in the future DBA/Developer may manually change its state to deferred.
Initially Deferred -- upon creation of the constraint, its action will be
POSTPONED(DEFERRED)
till COMMIT time and also may be later manually switched to the immediate one.
Syntax Part for defining constraint Type, State and Mode when doing it In-Line (with the column
together) is:
column_name DATATYPE [(maxlength)] [ CONSTRAINT constraint_name ] TYPE ...
[ {NOT DEFERRABLE | DEFERRABLE INITIALLY {IMMEDIATE | DEFERRED}} ]
[ {ENABLE {VALIDATE | NOVALIDATE} | DISABLE {NOVALIDATE | VALIDATE}} ]
How to Switch a Deferrable constraint to the Deferred/Immediate one-- Two Levels exist:
1. Session level will set all Deferrable constraints created as Initally Immediate to become
Deferred with:
ALTER SESSION SET CONSTRAINTS = DEFERRED;
or in the opposite case will set all Deferrable constraints created as Initially Deferred to
become Immediate with:
ALTER SESSION SET CONSTRAINTS = IMMEDIATE;
2. Database level will set either any individual constraint(s) or all of them to become Deferred
or Immediate with:
SET CONSTRAINT {constraint1, constraint2 ... | ALL} {DEFERRED | IMMEDIATE};
Guidelines for Defining constraints:
1. Place Indexes created by Server (that enforce PK/UK constraints) in the separate tablespace
from table data
by specifying USING INDEX TABLESPACE tbsp_name when you create a PK/UK
constraint
2. If huge data loads are expected for the table with PK/UK constraints, they may be created as
DEFERRABLE
and then the support Index will be NONUNIQUE, meaning that if the constraint is disabled
before that
load, the support Index will NOT be dropped and after enabling the constraint it will be still
active
Features of setting the constraint state to Enable Novalidate:
It puts NO LOCKS on a table, it is much faster than Validate state (does NOT check the existing
data),
In order for PK/UK constraints to be enforced they had to be created as DEFERRABLE and this
command
should be used when there is lots of DML activity going on; the comand for this setting is:
ALTER TABLE [user].table_name ENABLE NOVALIDATE CONSTRAINT
constraint_name; OR
ALTER TABLE [user].table_name MODIFY CONSTRAINT constraint_name ENABLE
NOVALIDATE;
Features of setting the constraint state to Enable Validate:
It LOCKS whole table if going from DISABLE state (that is why you should do firstly ENABLE
NOVALIDATE),
it is much slower than setting to Novalidate (it checks BOTH the incoming and he existing
data),
PK/UK constraints will be enforced in either Mode and this command should be used when NO
or MINIMAL
activity is going on; the comand for this setting is:
ALTER TABLE [user].table_name ENABLE [VALIDATE] CONSTRAINT constraint_name;
OR
ALTER TABLE [user].table_name MODIFY CONSTRAINT constraint_name ENABLE
[VALIDATE];
Six Steps Recipe to identify rows that are involved in the constraint violation:
1. Create table EXCEPTIONS in the SYS schema by running the script utlexcpt.sql
2. Execute the following command:
ALTER TABLE [user].table_name ENABLE CONSTRAINT constraint_name
EXCEPTIONS INTO EXCEPTIONS; --> will fail
3. Execute the following command:
ALTER TABLE [user].table_name ENABLE NOVALIDATE CONSTRAINT
constraint_name;
--> will be successfull if Constraint was created as DEFERRABLE
4. Identify invalid rows (their ROWID) by using a Subquery method
5. Rectify the errors by supplyuing the invalid row's ROWID in the WHERE clause of your
UPDATE statement
6. Truncate Exceptions table and perform Step2 again --> will success
Important Data Dictionary views are: DBA_CONSTRAINTS, DBA_CONS_COLUMNS
Week 10:
Lesson 7: MANAGING USERS AND PROFILES
Lesson 7: SYSTEM and OBJECT PRIVILEGES , also MANAGING ROLES
Commands/Content:
Week 11:
Lesson 14: BACKUP AND RECOVERY CONCEPTS
Commands/Content:
Week 12:
Lesson 15: PERFORMING and MANAGING DATABASE BACKUPS
Assignment Two is due
Commands/Content:
Week 13:
Lesson 16: PERFORMING DATABASE RECOVERY
Commands/Content:
FINAL EXAM is on Friday, April 11th – you may bring ONE reference sheet, both
sides, printed or handwritten