Redo log files are filled with redo records. A redo record also called a redo entry, is made up of a group of change vectors, each of which is a description of a change made to a single block in the database. For example, if you change a salary value in an employee table, you generate a redo record containing change vectors that describe changes to the data segment block for the table, the undo segment data block, and the transaction table of the undo segments.
Redo entries record data that you can use to reconstruct all changes made to the database, including the undo segments. Therefore, the redo log also protects rollback data. When you recover the database using redo data, the database reads the change vectors in the redo records and applies the changes to the relevant blocks.
SQL> select * from v$log;
SQL> select group#,status,sequence# from v$log;
GROUP# STATUS SEQUENCE#
---------- ---------------- ----------
1 CURRENT 91
2 INACTIVE 89
3 INACTIVE 90
SQL> select * from v$logfile;
Active (Current) and Inactive Redo Log Files
Oracle Database uses only one redo log file at a time to store redo records written from the redo log buffer. The redo log file that LGWR is actively writing to is called the current redo log file.
Redo log files that are required for instance recovery are called active redo log files. Redo log files that are no longer required for instance recovery are called inactive redo log files.
If you have enabled archiving (the database is in ARCHIVELOG mode), then the database cannot reuse or overwrite an active online log file until one of the archiver background processes (ARCn) has archived its contents. If archiving is disabled (the database is in NOARCHIVELOG mode), then when the last redo log file is full, LGWR continues by overwriting the first available active file.
Add New redo log file
SQL> alter database add logfile group 4 '/u01/app/oracle/oradata/TESTDB/redo04.dbf' size 100m;
Database altered.
Add Member to an existing group
SQL> alter database add logfile member '/u01/app/oracle/oradata/TESTDB/redo04b.log' to group 4;
Database altered.
Drop member
SQL> alter database drop logfile member '/u01/app/oracle/oradata/TESTDB/redo04b.log';
Database altered.
Drop Logfile Group
SQL> alter database drop logfile group 4;
Database altered.
SQL> select group#,status from v$log;
GROUP# STATUS
---------- ----------------
1 CURRENT
2 INACTIVE
3 INACTIVE
Adding Two member
SQL> alter database add logfile group 4 ('/u01/app/oracle/oradata/TESTDB/redo04a.log', '/u01/app/oracle/oradata/TESTDB/redo04C.log') size 100m;
Database altered.
SQL> select group#,member from v$logfile;
GROUP# MEMBER
---------- ---------------------------
4 /u01/app/oracle/oradata/TESTDB/redo04a.log
4 /u01/app/oracle/oradata/TESTDB/redo04C.log
Log Switches and Log Sequence Numbers
A log switch is a point at which the database stops writing to one redo log file and begins writing to another. Normally, a log switch occurs when the current redo log file is completely filled and writing must continue to the next redo log file. However, you can configure log switches to occur at regular intervals, regardless of whether the current redo log file is completely filled. You can also force log switches manually.
Oracle Database assigns each redo log file a new log sequence number every time a log switch occurs and LGWR begins writing to it. When the database archives redo log files, the archived log retains its log sequence number. A redo log file that is cycled back for use is given the next available log sequence number.
Each online or archived redo log file is uniquely identified by its log sequence number. During a crash, instance, or media recovery, the database properly applies to redo log files in ascending order by using the log sequence number of the necessary archived and redo log files.
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In this blog, we will see how to upgrade Oracle Database 12c to 19c using AutoUpgrade Tool
What is the AutoUpgrade?
The Oracle Database AutoUpgrade utility is a small command-line tool that allows you to upgrade your databases very easily with very little interaction
The new AutoUpgrade utility in Oracle 19¢ performs almost 99% of the task by itself, we just have to provide inputs during the initial phase
So it performs Prechecks against multiple databases, upgrades multiple databases in one go
Also, it does Post upgrade, object recompilation, and time zone up-gradation
The only thing you need to provide is a contig file in text format
Which database releases are supported?
As a source, the minimum version is Oracle Database 11.2.0.4. onwards
Download the latest auto-upgrade jar file
Auto upgrade utility autoupgrade.jar file exists by default under $ORACLE_HOME/rdbms/admin directory of Oracle 19c Home
Oracle strongly recommends downloading the latest AutoUpgrade version before doing the upgrade
You download the most recent version from MOS Note: 2485487.1 AutoUpgrade Tool
Once you download this jar file transfer it to the Server and create a new directory and place this file in that directory
prddb_config.cfg file should have following entry which specifies source and target database home location and DB name and log locations and other information’s:
Auto upgrade Analyze mode checks your database to see if it is ready for the upgrade. This will reads data from the database and does not perform any updates.
Execute AutoUpgrade in analyze mode with the below syntax:
Once the upgrade process is started consider monitoring the logs and database alert logs to see the progress of the upgrade. Auto upgrade logs are available under
/home/oracle/auto_upgrade_19c/upg_logs/
Once the upgrade finishes crosscheck the below.
SELECT VERSION FROM V$TIMEZONE_FILE;
select name, open_mode, version, status from v$database, v$instance;
Post-upgrade task
Once the upgrade is successful and all testing is done, drop the restore point.
Drop the Guaranteed restore point
select name from v$restore_point;
drop restore point restorepoint_name;
Change the compatible parameter
After the upgrade, the database has to be tested properly before updating the compatible parameter. Once the parameter is updated database cannot be downgraded.
show parameter compatible;
alter system set compatible=’19.0.0′ scope=spfile;
shutdown immediate:
startup;
show parameter compatible;
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How to find the bind variable values of the SQL statement using SQLID?
SELECT sql_id, b.name BIND_NAME, b.value_string BIND_STRING from gv$sql t
JOIN gv$sql_bind_capture b USING (sql_id) WHERE b.value_string IS NOT NULL
AND sql_id ='&SQLID';
Additional script which may be helpful at a later point in time:
To know the last executed query in the oracle and its hash value,sqlid
SELECT * FROM v$SQLTEXT_WITH_NEWLINES WHERE address =
(SELECT prev_sql_addr FROM v$session WHERE audsid = userenv('SESSIONID'))
ORDER BY piece;
To know the SQL plan history of a sql using the sqlid:
select * from TABLE(DBMS_XPLAN.DISPLAY_AWR('&sqlid'));
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Once you have configured the flash recovery area, you can put the database in ARCHIVELOG mode. Unfortunately, this requires that the database be shutdown first with the shutdown command (however, from earlier in the chapter, we note that shutdown immediate is the best option). Once you have shutdown the database, you will start the database in mount Stage with the startup mount command. Then put the database in ARCHIVELOG mode, and finally open the database. Here is an example of how this all works from the command line.
SQL> archive log list;
Database log mode No Archive ModeAutomatic archival Disabled
Archive destination d:oracleoradataDB10Garchive
Oldest online log sequence 427
Current log sequence 429
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
Total System Global Area 1610609200 bytes
Fixed Size 8897072 bytes
Variable Size 385875968 bytes
Database Buffers 1207959552 bytes
Redo Buffers 7876608 bytes
Database mounted.
SQL> alter database archivelog;
Database altered.
SQL> alter database open;
Database altered.
SQL> archive log list;
Database log mode Archive Mode
Automatic archival Enabled
Archive destination d:oracleoradataDB10Garchive
Oldest online log sequence 426
Next log sequence to archive 427
Current log sequence 428
How to Disable archive log mode
SQL> archive log list;
Database log mode Archive Mode
Automatic archival Enabled
Archive destination d:oracleoradataDB10Garchive
Oldest online log sequence 426
Next log sequence to archive 427
Current log sequence 428
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
Total System Global Area 1610609200 bytes
Fixed Size 8897072 bytes
Variable Size 385875968 bytes
Database Buffers 1207959552 bytes
Redo Buffers 7876608 bytes
Database mounted.
SQL> alter database noarchivelog;Database altered.
SQL> alter database open;
Database altered.
SQL> archive log list;
Database log mode NoArchive Mode
Automatic archival Enabled
Archive destination d:oracleoradataDB10Garchive
Oldest online log sequence 426
Next log sequence to archive 427
Current log sequence 428
Change Archive log mode and Destination in oracle 19c
[oracle@training ~]$ export ORACLE_SID=training1
[oracle@training ~]$ sqlplus / as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Wed Jul 28 23:30:16 2021
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Connected to an idle instance.
SQL> startup
ORACLE instance started.
Total System Global Area 2432695144 bytes
Fixed Size 8899432 bytes
Variable Size 536870912 bytes
Database Buffers 1879048192 bytes
Redo Buffers 7876608 bytes
Database mounted.
Database opened.
SQL> exit
Disconnected from Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production Version 19.3.0.0.0
[oracle@training ~]$ mkdir -p /u01/ARC_BKP
[oracle@training ~]$ sqlplus / as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Wed Jul 28 23:38:09 2021
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0
To check the current archiving location
SQL> SHOW PARAMETER DB_RECOVERY_FILE_DEST
NAME TYPE VALUE
--------------------- --------------- --------------
db_recovery_file_dest string /u01/app/oracle /fast_recovery_area
db_recovery_file_dest_size big integer 8256M
SQL> alter system set DB_RECOVERY_FILE_DEST='/u01/ARC_BKP';
System altered.
SQL> alter system set log_archive_dest=’/u01/ARC_BKP’;
System altered.
SQL> alter database close;
Database altered.
SQL> alter database archivelog;
Database altered.
SQL> shut immediate
ORA-01109: database not open
Database dismounted.
ORACLE instance shut down.
SQL> exit
Disconnected from Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production Version 19.3.0.0.0
[oracle@training u01]$ sqlplus / as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Wed Jul 28 23:52:05 2021
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Connected to an idle instance.
SQL> startup
ORACLE instance started.
Total System Global Area 2432695144 bytes
Fixed Size 8899432 bytes
Variable Size 536870912 bytes
Database Buffers 1879048192 bytes
Redo Buffers 7876608 bytes
Database mounted.
Database opened.
SQL> archive log list;
Database log mode Archive Mode
Automatic archival Enabled
Archive destination /u01/ARC_BKP
Oldest online log sequence 89
Next log sequence to archive 91
Current log sequence 91
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SQL> select name from v$controlfile;
NAME
------------------------------------------------------------------
/u01/app/oracle/oradata/TRAINING/controlfile/o1_mf_j9bdm6dk_.ctl
/u01/app/oracle/oradata/TRAINING/controlfile/o1_mf_j9bdm6dk_1.ctl
SQL> alter system set control_files= '/u01/app/oracle/oradata/TRAINING/controlfile/o1_mf_j9bdm6dk_.ctl', '/u01/app/oracle/oradata/TRAINING/controlfile/o1_mf_j9bdm6dk_1.ctl', '/u01/app/oracle/oradata/TRAINING/control01.dbf' scope=spfile;
System altered.
SQL> startup
ORACLE instance started.
Total System Global Area 2432695144 bytes
Fixed Size 8899432 bytes
Variable Size 536870912 bytes
Database Buffers 1879048192 bytes
Redo Buffers 7876608 bytes
Database mounted.
Database opened.
SQL> select name from v$controlfile;
NAME
--------------------------------------------------------------------------------
/u01/app/oracle/oradata/TRAINING/controlfile/o1_mf_j9bdm6dk_.ctl
/u01/app/oracle/oradata/TRAINING/controlfile/o1_mf_j9bdm6dk_1.ctl
/u01/app/oracle/oradata/TRAINING/control01.dbf
SQL> create pfile from spfile;
File created.
MULTIPLEXING USING PFILE
Multiplexing is the process of mintaining a copy of same control files on different disk drivers (and idealy on different controllers). To multiplex your control files, we copy the control file to multiple locations and change the CONTROL_FILES parameter in the text based initialization file init.ora to include all control files names.
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> exit
Disconnected from Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production Version 19.3.0.0.0
[oracle@training ~]$ cd $ORACLE_HOME/dbs
[oracle@training dbs]$ vi inittraining.ora
*.control_files='/u01/app/oracle/oradata/TRAINING/controlfile/o1_mf_j9bdm6dk_.ctl', '/u01/app/oracle/oradata/TRAINING/controlfile/o1_mf_j9bdm6dk_1.ctl', '/u01/app/oracle/oradata/TRAINING/control01.dbf'
[oracle@training dbs]$ cp /u01/app/oracle/oradata/TRAINING/control01.dbf /u01/app/oracle/oradata/TRAINING/control02.dbf
[oracle@training dbs]$ sqlplus / as sysdba
SQL> startup pfile=$ORACLE_HOME/dbs/inittraining1.ora
ORACLE instance started.
Total System Global Area 2432695144 bytes
Fixed Size 8899432 bytes
Variable Size 536870912 bytes
Database Buffers 1879048192 bytes
Redo Buffers 7876608 bytes
Database mounted.
Database opened.
SQL> select name from v$controlfile;
NAME
--------------------------------------------------------------------------------
/u01/app/oracle/oradata/TRAINING1/controlfile/o1_mf_j9bdm6dk_.ctl
/u01/app/oracle/oradata/TRAINING1/controlfile/o1_mf_j9bdm6dk_1.ctl
/u01/app/oracle/oradata/TRAINING1/control01.dbf
/u01/app/oracle/oradata/TRAINING1/control02.dbf
SQL> create spfile from pfile;
File created.
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DBNEWID is a database utility, in $ORACLE_HOME/bin directory, that can change the internal database identifier (DBID) and the database name (DBNAME) for an operational database. Prior to the introduction of the DBNEWID utility, we used to manually create a copy of a database and give it a new database name (DBNAME) by re-creating the control file. However, alteration of the internal database identifier (DBID) of an instance was impossible.
The DBID is an internal, unique identifier for a database. Because Recovery Manager(RMAN) distinguishes databases by DBID, you could not register a seed database and a manually copied database together in the same RMAN repository. The DBNEWID utility solves this problem.
NID utility allows us to change
Only DBID of a database
Only DBNAME of a database
Both DBNAME and DBID of a database
Changing the DBID of a database is a serious procedure. When the DBID of a database is changed all previous backups and archived logs of the database become unusable. After you change the DBID, you must open the database with the RESETLOGS option, which re-creates the online redo logs and resets their sequence to 1. Consequently, you should make a backup of the whole database immediately after changing the DBID.
Changing DBNAME & DBID
SQL> select dbid, name from v$database;
DBID NAME
---------- ---------
247698686 TRAINING
SQL> SHUTDOWN IMMEDIATE
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> STARTUP MOUNT
ORACLE instance started.
Total System Global Area 2432695144 bytes
Fixed Size 8899432 bytes
Variable Size 536870912 bytes
Database Buffers 1879048192 bytes
Redo Buffers 7876608 bytes
Database mounted.
SQL> exit
Disconnected from Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0
[oracle@training ~]$ nid TARGET=sqlplus / as sysdba DBNAME=testdb LOGFILE=testdb.log
Password:
SQL> select status from v$instance;
STATUS
------------
STARTED
SQL> alter database mount;
alter database mount
*
ERROR at line 1:
ORA-01103: database name 'TESTDB' in control file is not 'TRAINING'
[oracle@training dbs]$ . oraenv
ORACLE_SID = [training] ?
The Oracle base remains unchanged with value /u01/app/oracle
[oracle@training dbs]$ sqlplus / as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Thu Jul 29 02:57:59 2021
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Connected to an idle instance.
SQL> startup pfile=$ORACLE_HOME/dbs/inittraining.ora
ORACLE instance started.
Total System Global Area 2432695144 bytes
Fixed Size 8899432 bytes
Variable Size 536870912 bytes
Database Buffers 1879048192 bytes
Redo Buffers 7876608 bytes
Database mounted.
ORA-01589: must use RESETLOGS or NORESETLOGS option for database open
SQL> alter database open resetlogs;
Database altered.
SQL> select dbid,name from v$database;
DBID NAME
---------- ---------
2862448691 TESTDB
SQL> select status,instance_name from v$instance;
STATUS INSTANCE_NAME
------------ ----------------
OPEN training
SQL> create spfile from pfile;
File created.
SQL> show parameter spfile;
NAME TYPE VALUE
------------- ----------- ------------------------------
spfile string /u01/app/oracle/product/19.0.0
/dbhome_1/dbs/spfiletraining.ora
Change the only DBNAME
SQL> shut immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
Total System Global Area 2432695144 bytes
Fixed Size 8899432 bytes
Variable Size 536870912 bytes
Database Buffers 1879048192 bytes
Redo Buffers 7876608 bytes
Database mounted.
SQL> exit
Disconnected from Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production Version 19.3.0.0.0
[oracle@training ~]$ nid target=sqlplus / as sysdba dbname=training setname=yes
DBNEWID: Release 19.0.0.0.0 - Production on Thu Jul 29 21:48:14 2021
Copyright (c) 1982, 2019, Oracle and/or its affiliates. All rights reserved.
Password:
Connected to database TESTDB (DBID=2862448691)
Connected to server version 19.3.0
Control Files in database:
/u01/app/oracle/oradata/TRAINING1/control01.dbf
/u01/app/oracle/oradata/TRAINING1/control02.dbf
Change database name of database TESTDB to TRAINING? (Y/[N]) => y
Proceeding with operation
Changing database name from TESTDB to TRAINING
Control File /u01/app/oracle/oradata/TRAINING1/control01.dbf -modified
Control File/u01/app/oracle/oradata/TRAINING1/control02.dbf - modified
Datafile /u01/app/oracle/oradata/TRAINING1/system.dbf - wrote new name
Datafile /u01/app/oracle/oradata/TRAINING1/sysaux.dbf - wrote new name
Datafile /u01/app/oracle/oradata/TRAINING1/undo.dbf - wrote new name
Datafile /u01/app/oracle/oradata/TRAINING1/users.dbf - wrote new name
Datafile /u01/app/oracle/oradata/TRAINING1/temp.tmp - wrote new name
Instance shut down
Database name changed to TRAINING.
Modify parameter file and generate a new password file before restarting.
Succesfully changed database name.
DBNEWID - Completed succesfully.
[oracle@training dbs]$ . oraenv
ORACLE_SID = [training1] ?
The Oracle base remains unchanged with value /u01/app/oracle
[oracle@training dbs]$ sqlplus / as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Thu Jul 29 21:52:50 2021
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Connected to an idle instance.
SQL> startup pfile='$ORACLE_HOME/dbs/inittraining1.ora'
ORACLE instance started.
Total System Global Area 2432695144 bytes
Fixed Size 8899432 bytes
Variable Size 536870912 bytes
Database Buffers 1879048192 bytes
Redo Buffers 7876608 bytes
Database mounted.
Database opened.
SQL> select name from v$database;
NAME
---------
TRAINING
SQL> select status,instance_name from v$instance;
STATUS INSTANCE_NAME
--------- ----------------
OPEN training1
Change only DBID
SQL> shut immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
Total System Global Area 2432695144 bytes
Fixed Size 8899432 bytes
Variable Size 536870912 bytes
Database Buffers 1879048192 bytes
Redo Buffers 7876608 bytes
Database mounted.
SQL> exit
Disconnected from Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production Version 19.3.0.0.0
[oracle@training dbs]$ nid target=sqlplus / as sysdba
DBNEWID: Release 19.0.0.0.0 - Production on Thu Jul 29 22:58:56 2021
Copyright (c) 1982, 2019, Oracle and/or its affiliates. All rights reserved.
Password:
Connected to database TRAINING (DBID=2862448691)
Connected to server version 19.3.0
Control Files in database:
/u01/app/oracle/oradata/TRAINING1/control01.dbf
/u01/app/oracle/oradata/TRAINING1/control02.dbf
Change database ID of database TRAINING? (Y/[N]) => y
Proceeding with operation
Changing database ID from 2862448691 to 254963316
Control File /u01/app/oracle/oradata/TRAINING1/control01.dbf - modified
Control File /u01/app/oracle/oradata/TRAINING1/control02.dbf - modified
Datafile /u01/app/oracle/oradata/TRAINING1/system.dbf - dbid changed
Datafile /u01/app/oracle/oradata/TRAINING1/sysaux..dbf - dbid changed
Datafile /u01/app/oracle/oradata/TRAINING1/undo.dbf - dbid changed
Datafile /u01/app/oracle/oradata/TRAINING1/users.dbf - dbid changed
Datafile /u01/app/oracle/oradata/TRAINING1/data01.dbf - dbid changed
Datafile /u01/app/oracle/oradata/TRAINING1/temp.tmp - dbid changed
Control File /u01/app/oracle/oradata/TRAINING1/control01.dbf - dbid changed
Control File /u01/app/oracle/oradata/TRAINING1/control02.dbf - dbid changed
Instance shut down
Database ID for database TRAINING changed to 254963316.
All previous backups and archived redo logs for this database are unusable.
Database is not aware of previous backups and archived logs in Recovery Area.
Database has been shutdown, open database with RESETLOGS option.
Succesfully changed database ID.
DBNEWID - Completed successfully.
[oracle@training dbs]$ sqlplus / as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Thu Jul 29 22:59:46 2021
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Connected to an idle instance.
SQL> startup mount;
ORACLE instance started.
Total System Global Area 2432695144 bytes
Fixed Size 8899432 bytes
Variable Size 536870912 bytes
Database Buffers 1879048192 bytes
Redo Buffers 7876608 bytes
Database mounted.
SQL> alter database open resetlogs;
Database altered.
SQL> select name,dbid from v$database;
NAME DBID
--------- ----------
TRAINING 254963316
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The LMT tablespace is implemented by adding EXTENT MANAGEMENT LOCAL clause to the tablespace definition.LMT tablespaces automate extent management and remove the ability to specify the NEXT storage parameter.
The only exception is when NEXT is used with MINEXTENTS at table creation time.
LMT means Locally Management system,LMT tablespace size is uniform.
By default uniform size is 1,By default lmt tablespace is Autoallocate.
Auto allocate
SQL> create tablespace india datafile '/u01/app/oracle/oradata/TESTDB/india01.dbf' size 50m;
Tablespace created.
Uniform Size
SQL> create tablespace USA datafile '/u01/app/oracle/oradata/TESTDB/USA01.dbf' size 50m extent management local uniform size 512k;
Tablespace created.
Deferred segment creation
SQL> create table india (reg_id number,reg_name varchar2(200));
Table created.
SQL> select count(*) from dba_segments where segment_name='INDIA';
COUNT(*)
----------
0
SQL> select count(*) from dba_extents where segment_name='INDIA';
COUNT(*)
----------
0
SQL> insert into india values (5,'tamil');
1 row created.
SQL> select count(*) from dba_segments where segment_name='INDIA';
COUNT(*)
----------
1
SQL> select count(*) from dba_extents where segment_name='INDIA';
COUNT(*)
----------
1
SQL> create table italy (reg_no number,reg_name varchar2(2000))
segment creation immediate;
Table created.
SQL> show parameter deferred_segment_creation;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
deferred_segment_creation boolean TRUE
SQL> alter system set deferred_segment_creation=false;
System altered.
SQL> show parameter deferred_segment_creation;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
deferred_segment_creation boolean FALSE
Extents
Continuous blocks it’s called extents,Data Stored in blocks,blocks Stored in extents.
By default Extents Size 64k.
TYPES OF EXTENTS
Initial - Initial is First No of transaction by default 100.
Next - Next no of transaction is 200.
Minextents - minimum number of transactions by default 1.
Maxextents - maximum number of transactions by default Unlimited.
Pct increase - pct increase by default 100.
BLOCKS
Smallest storage unit it’s called Blocks.After database creation we can specify block size but before database creation we can’t change block size. block size is 2k,4k,8k,16k,32k. By default Block size is 8k.
Check Block Size in Database
SQL> show parameter db_block_size;
NAME TYPE VALUE
--------------------- ----------- --------------
db_block_size integer 8192
SQL> select block_size,tablespace_name from dba_tablespaces;
BLOCK_SIZE TABLESPACE_NAME
---------- ------------------------------
8192 SYSTEM
8192 SYSAUX
8192 UNDOTBS1
8192 TEMP
8192 USERS
8192 TEST
8192 INDIA
SQL> select block_size,tablespace_name from dba_tablespaces;
BLOCK_SIZE TABLESPACE_NAME
---------- ---------------------
8192 SYSTEM
8192 SYSAUX
8192 UNDOTBS1
8192 TEMP
8192 USERS
8192 TEST
8192 INDIA
16384 SPAIN
Block Utilization Parameters
INITRANS
MAXTRANS
PCTUSED
PCTFREE
Initans is the initial number of transactions by default 1. Maxtrans is Maximum number of Transactions default 255.Inserted data Stored in pct used by default allocate space is 89%, in case pct used is full Remaining data goes to Next pct used. Update happens in pct free by default allocate space 10%, pct used and pct free information stored by block header by default allocated space 1%.
Block-level problems
Row chaining
Row migration
Row chaining
Inserted data stored in pct used,that pct used is full remaining data goes to next pct used it is called Row chaining.Row chaining occurs when a row can't physically fit into an Oracle block.
Another block is required to store the remainder of the row.Chaining can cause serious performance problems and is especially prevalent with those storing multimedia data or large binary objects (blobs).
You should pay special attention to the DB_BLOCK_SIZE parameter when you create your database.Block sizes of 4 kilobytes or more are the norm, not the exception.
Row migration
Date updates happen for pct free ,that updated data stored in pct used.pct used is full that time remaining data goes to the next pct used that is called row Migration.
Migration of an Oracle row occurs when a row is updated in an Oracle block and the amount of free space in the block is not adequate to store all of the row's data. The row is migrated to another physical block in the table. The problem is that the indexes that refer to the migrated row are still pointing to the block where the row used to be, and hence the table reads are doubled. Note however that full table scans will scan blocks as they come and will perform the same number of reads whether the rows are migrated or not.
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Below Query will convert all the unusable and not valid indexes in Oracle. The query will cover the complete index with partition index and subpartition index.
The result will give you the rebuild command of the invalid or unusable indexes.
You can directly run that and on sqlplus and make them a valid or usable state.
QUERY :
SELECT 'ALTER INDEX ' || OWNER || '.' ||
INDEX_NAME || ' REBUILD ' ||
' TABLESPACE ' || TABLESPACE_NAME || ';'
FROM DBA_INDEXES
WHERE STATUS='UNUSABLE'
UNION
SELECT 'ALTER INDEX ' || INDEX_OWNER || '.' ||
INDEX_NAME ||
' REBUILD PARTITION ' || PARTITION_NAME ||
' TABLESPACE ' || TABLESPACE_NAME || ';'
FROM DBA_IND_PARTITIONS
WHERE STATUS='UNUSABLE'
UNION
SELECT 'ALTER INDEX ' || INDEX_OWNER || '.' ||
INDEX_NAME ||
' REBUILD SUBPARTITION '||SUBPARTITION_NAME||
' TABLESPACE ' || TABLESPACE_NAME || ';'
FROM DBA_IND_SUBPARTITIONS
WHERE STATUS='UNUSABLE';
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Flashback version query allows the versions of a specific row to be tracked during a specified time period using the VERSIONS BETWEEN clause.
Flashback version query is based on UNDO. As a result, the amount of time you can flashback is dependent on how long undo information is retained, as specified by the UNDO_RETENTION parameter.
SQL> CREATE TABLE flashback_version_query_test (id NUMBER(10),description VARCHAR2(50));
Table created.
SQL> INSERT INTO flashback_version_query_test (id, description) VALUES (1, 'ONE');
1 row created.
SQL> commit;
Commit complete.
SQL> SELECT current_scn, TO_CHAR(SYSTIMESTAMP, 'YYYY-MM-DD HH24:MI:SS') FROM v$database;
CURRENT_SCN TO_CHAR(SYSTIMESTAM
----------- -------------------
4991867 2021-07-20 22:29:52
SQL> UPDATE flashback_version_query_test SET description = 'TWO' WHERE id = 1;
1 row updated.
SQL> commit;
Commit complete.
SQL> UPDATE flashback_version_query_test SET description = 'THREE' WHERE id = 1;
1 row updated.
SQL> commit;
Commit complete.
SQL> SELECT current_scn, TO_CHAR(SYSTIMESTAMP, 'YYYY-MM-DD HH24:MI:SS') FROM v$database;
CURRENT_SCN TO_CHAR(SYSTIMESTAM
----------- -------------------
4992195 2021-07-20 22:34:30
SQL> SELECT versions_startscn, versions_starttime,versions_endscn, versions_endtime, versions_xid, versions_operation, description from flashback_version_query_test VERSIONS BETWEEN TIMESTAMP TO_TIMESTAMP(' 2021-07-20 22:29:52', 'YYYY-MM-DD HH24:MI:SS') AND TO_TIMESTAMP('2021-07-20 22:34:30', 'YYYY-MM-DD HH24:MI:SS')WHERE id = 1;
VERSIONS_STARTSCN VERSIONS_STARTTIME VERSIONS_ENDSCN VERSIONS_ENDTIME VERSIONS_XID V DESCRIPTION
---------- --------------------- ------------------ -------------- ----------- -----------
4992172 20-JUL-21 10.33.41 PM 0D0020001B040000 U THREE
4992136 20-JUL-21 10.32.23 PM 0B00050021040000 U TWO
4992172 20-JUL-21 10.33.41 PM ONE
SQL> SELECT versions_startscn, versions_starttime, versions_endscn, versions_endtime, versions_xid, versions_operation, description FROM flashback_version_query_test
VERSIONS BETWEEN SCN 4991867 and 4992195 WHERE id = 1;
VERSIONS_STARTSCN VERSIONS_STARTTIME VERSIONS_ENDSCN VERSIONS_ENDTIME VERSIONS_XID V DESCRIPTION
------------------ ------------------------ ------------------ ------------------------ ---------------- - -----------
4992172 20-JUL-21 10.33.41 PM 0D0020001B040000 U THREE
4992136 20-JUL-21 10.32.23 PM 4992172 20-JUL-21 10.33.41 PM 0B00050021040000 U TWO
4992136 20-JUL-21 10.32.23 PM ONE
SQL> SELECT xid, operation, start_scn,commit_scn, logon_user, undo_sql FROM flashback_transaction_query WHERE xid = HEXTORAW('06000000FA030000');
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The recycle bin is a logical collection of previously dropped objects. This feature doesn’t use flashback logs or undo, so it is distinct from the other flashback technologies.
Enable/Disable Recycle Bin
SQL> show parameter recyclebin;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
recyclebin string OFF
SQL> alter session set recyclebin = on;
Session altered.
SQL> show parameter recyclebin;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
recyclebin string ON
(RECYCLE BIN)
SQL> CREATE TABLE flashback_drop_test (id NUMBER(10));
Table created.
SQL> INSERT INTO flashback_drop_test (id) VALUES (1);
1 row created.
SQL> commit;
Commit complete.
SQL> DROP TABLE flashback_drop_test;
Table dropped.
SQL> show recyclebin;
ORIGINAL NAME RECYCLEBIN NAME OBJECT TYPE DROP TIME
---------------- ------------------------------ ------------ -------------------
FLASHBACK_DROP_T BIN$TstgCMiwQA66fl5FFDTBgA==$0 TABLE 2004-03-29:11:09:07
EST
SQL> FLASHBACK TABLE flashback_drop_test TO BEFORE DROP;
SELECT * FROM flashback_drop_test;
ID
----------
1
Rename Table
SQL> show RECYCLEBIN;
ORIGINAL NAME RECYCLEBIN NAME OBJECT TYPE DROP TIME
---------------- ------------------------------ ------------ -------------------
S BIN$x3mKgoseD/7gUxkBqMAnAA==$0 TABLE 2021-07-19:17:20:17
SQL> create table s(n number);
Table created.
SQL> FLASHBACK TABLE s TO BEFORE DROP;
FLASHBACK TABLE s TO BEFORE DROP
*
ERROR at line 1:
ORA-38312: original name is used by an existing object
SQL> FLASHBACK TABLE s TO BEFORE DROP rename to b;
Flashback complete.
SQL> select * from b;
no rows selected
SQL> show RECYCLEBIN;
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