de haan - flash me back, scotty

©2005, Natural Join B.V. Flash Me Back, Scotty - 1

HotsosSymposiumDallas, March 2005

Oracle Database 10g:Flash Me Back, Scotty …

Lex de Haan([email protected])

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Who Am I

Lex de [email protected] Maths, TU DelftOracle employee 1990-2004

– Teacher, delivery manager,product manager seminars,curriculum developer/manager,ST development

ISO SQL StandardizationMarch 2004: Natural Join B.V.http://www.naturaljoin.nl


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Topics

1. Flashback (Versions) Query– Flashback pseudocolumns– Guaranteed undo retention– SCN <=> TIMESTAMP conversion functions

2. Flashback transaction query3. Flashback table

4. Flashback drop– The recyclebin– Purging the recyclebin

5. Flashback database

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Flashback (Versions) Query

Retrieve row versions back in time from undo segments

Purposes:– Table

auditing– Transaction

miningLevels:

– Statementlevel

– Sessionlevel

select ... from ...VERSIONS BETWEEN{SCN {n|MINVALUE} AND {m|MAXVALUE}|TIMESTAMP t1 AND t2 }where ...

select ... from ...AS OF {SCN n|TIMESTAMP t}where ...

dbms_flashback.ENABLE_AT_TIME(t);...dbms_flashback.DISABLE;

1.


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Flashback Versions Pseudocolumns

Operation that produced the versionVERSIONS_OPERATION

Transaction that created the version(useful for further investigations)VERSIONS_XID

Version validity range: Upper boundVERSIONS_ENDTIME

VERSIONS_ENDSCN

Version validity range: Lower boundVERSIONS_STARTTIME

VERSIONS_STARTSCN

DescriptionPseudocolumn

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Guaranteed Undo Retention

SQL> alter tablespace undotbs12 RETENTION [NO]GUARANTEE;

SQL> select tablespace_name, RETENTION2 from dba_tablespaces;

TABLESPACE_NAME RETENTION--------------- ---------UNDOTBS1 GUARANTEE... ...


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New SQL Conversion Functions

Precision: about 3 secondsRetention: minimum 5 days (depends on undo retention)

SQL> select current_scn,2 SCN_TO_TIMESTAMP(current_scn)3 from v$database;

CURRENT_SCN SCN_TO_TIMESTAMP(CURRENT_SCN)----------- -------------------------------

4479369 14-DEC-04 10.27.31.000000000 PM

TIMESTAMP -> NUMBERTIMESTAMP_TO_SCN

NUMBER -> TIMESTAMPSCN_TO_TIMESTAMP

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Flashback Transaction Query

View database changes at the transaction levelPerform transaction auditingRecover from user or application errorsDerived from undo segments; faster than LogMinerProtected by a system privilege

SQL> select operation, undo_sql, table_name2 from FLASHBACK_TRANSACTION_QUERY3 where xid = hextoraw('...');

SQL> select operation, undo_sql, table_name2 from FLASHBACK_TRANSACTION_QUERY3 where start_timestamp >= '...'4 and commit_timestamp <= '...';

2.


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Combining Flashback Versionsand Flashback Transaction

SQL> select operation, undo_sql

2 , table_name

3 from FLASHBACK_TRANSACTION_QUERY

4 where xid = hextoraw('xxxxxxxxxxxxxxxx');

SQL> select versions_xid

2 , salary

3 from hr.employees

4 versions between scn

5 minvalue and maxvalue

6 where last_name = 'De Haan';

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Flashback Table

Recover tables to a specific point in time: fast, easy, in-placeExecuted as a single-statement (autocommit) transactionExclusive DML table locks neededTriggers temporarily disabled by default; indexes maintainedRecorded in the alert log fileTip: Record the current SCN first (from v$database)

SQL> FLASHBACK TABLE hr.employees [, ...]2 TO {SCN n|TIMESTAMP t}3 [{ENABLE|DISABLE} TRIGGERS]

SQL> alter table hr.employees2 ENABLE ROW MOVEMENT;

3.


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Flashback Table: Error Messages

SQL> flashback table hr.employees to scn ...;flashback table hr.employees

*ERROR at line 1:ORA-02091: transaction rolled backORA-02291: integrity constraint(HR.EMP_JOB_FK)

violated - parent key not found

SQL> flashback table hr.jobs to scn ...;flashback table hr.jobs

*ERROR at line 1:ORA-02091: transaction rolled backORA-02292: integrity constraint(HR.EMP_JOB_FK)

violated - child record found

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Flashback Table: Error Messages

SQL> flashback table hr.jobs to scn ...;flashback table hr.jobs

*ERROR at line 1:ORA-01466: unable to read data -

table definition has changed

SQL> flashback table hr.employees to scn ...;flashback table hr.employees

*ERROR at line 1:ORA-08183: Flashback cannot be enabled in the

middle of a transaction


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Flashback Drop Feature

Tables (and any associated objects) are renamedand marked as dropped; space is not releasedFlashback drop does not depend on undoSeveral implicit purge policies(quota, space allocation algorithm)Recycle bin can be disabled with a hidden parameter

drop table employees;

FLASHBACK table employeesTO BEFORE DROP[RENAME TO ...];

4.

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Flashback Drop Feature

Drop objects without storing them in the recycle bin:

Query the recycle bin:

SQL> drop table <table_name> PURGE;

SQL> select * from [USER_|DBA_]RECYCLEBIN;

SQL> show recyclebin [original_name]


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Querying the Recycle Bin

You can query tables in the recycle bin using object namesTables in the recycle bin are read only

– Flashback queries are possible– Queries may fail with “ORA-1410: invalid ROWID”

SQL> select ...2 from "BIN$VoMP0begR7qB4RxzSz5CzQ==$0"3 [AS OF ...]4 where ...

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PURGE Command

SQL> purge {TABLE <table_name>|INDEX <index_name>};

SQL> purge TABLESPACE <ts_name>[USER <user_name>];

SQL> purge [USER_|DBA_]RECYCLEBIN;


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SQL Commands and Implicit Purging

The recycle bin is purged:– If you drop a tablespace or a user– If you reach your tablespace quota– If a tablespace needs more space (purge before extend)

SQL> drop TABLESPACE <ts_name>[including contents];

SQL> drop USER <user_name> [cascade]

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Flashback Database

Flashback database is much faster than point-in-timerecovery

– “Database rewind” functionalityUseful in cases of logical data corruptionUseful in Data Guard configurations

– Real time apply: enable flashback on standby db– Avoid recreating physical standby db after open resetlogs on

primary– Convert old primary db into a new standby db after a failover

For flashback database:– The database must be in archivelog mode– The database must be mounted exclusive

5.


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Flashback Database

You cannot use flashback database in the following situations:– The control file has been restored or re-created– A tablespace has been dropped– A data file has been shrunk– You recovered through a RESETLOGS operation

After flashback database, you can open the database:– In read-only mode, to verify that the desired situation is reached– With a RESETLOGS operation, to allow for updates

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Instance DatabaseFlash recovery area

Architectural Components

Flashback logs

Redo log files

LGWR

RVWRFlashbackbuffer

Redo logbuffer


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Defining a Flash Recovery Area

You define the flash recovery area by setting parameters:– DB_RECOVERY_FILE_DEST_SIZE (size, in bytes) – DB_RECOVERY_FILE_DEST (the location)– DB_FLASHBACK_RETENTION_TARGET (in mins; default 1 day)

Centralized area for recovery purposes

SQL> alter system set2 DB_RECOVERY_FILE_DEST_SIZE=64G scope=both;

SQL> alter system set2 DB_RECOVERY_FILE_DEST='/oradata/fr_area' scope=both;

SQL> select name, space_limit, space_used2 , space_reclaimable, number_of_files2 from V$RECOVERY_FILE_DEST;

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Configuring Flashback Database

1. Configureflash recovery area

3. Enableflashback database

2. Setretentiontarget

SQL> alter database FLASHBACK {ON|OFF};

SQL> select flashback_on, current_scn2 from v$database;


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Monitoring Flashback Database

Monitor the flashback database retention target;adjust flash recovery area size when needed

Monitor the overhead of logging flashback data(view contains 24 hours of information, one row per hour)

SQL> select oldest_flashback_scn2 , retention_target3 from V$FLASHBACK_DATABASE_LOG;

SQL> select begin_time, end_time2 , flashback_data, redo_data3 from V$FLASHBACK_DATABASE_STAT;

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Flashback Database: Examples

RMAN> flashback database 2> to TIME = to_date3> ('2004-08-11 16:15:14',4> 'YYYY-MM-DD HH24:MI:SS');

RMAN> flashback database to SCN=87654;

RMAN> flashback database 2> to SEQUENCE=42 THREAD=1;

SQL> flashback database 2 to TIMESTAMP (systimestamp-2/24);

SQL> flashback database to scn 76543;


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Errors During Flashback Database

SQL> flashback database to scn ...;ERROR at line 1: ORA-38729: Not enough flashback databaselog data to do FLASHBACK.

SQL> flashback database to scn ...;ERROR at line 1: ORA-38753: Cannot flashback data file 4;no flashback log data. ORA-01110: data file 4: '/oradata/10g/users01.dbf' ORA-38753: Cannot flashback data file 5;no flashback log data. ORA-01110: data file 5:'/oradata/10g/example01.dbf'

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Excluding Tablespacesfrom Flashback Database

If you disable flashback for a tablespace:– You must take it offline before you can perform a flashback

database– After flashback database: drop it, or recover the offline data files

with traditional point-in-time recovery

SQL> alter tablespace <ts> FLASHBACK {ON|OFF}

SQL> select tablespace_name, FLASHBACK_ON2 from v$tablespace;


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Granting Flashback Privileges

To use flashback features, you need the following privileges:

For flashback database:– SYSDBA database connection

For flashback table or flashback versions query:– FLASHBACK ANY TABLE

– Appropriate object privilegesFor flashback transaction query:

– SELECT ANY TRANSACTION

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By the Way …

Every Oracle table has a new pseudocolumn in 10g:

For maximum precision, for the price of six bytes per row:

SQL> select empno, ename, ORA_ROWSCN2 from scott.emp;

SQL> create table my_emp ROWDEPENDENCIES2 as select * from scott.emp;

SQL> select empno, ename2 , SCN_TO_TIMESTAMP(ORA_ROWSCN)3 from scott.emp;


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That’s All ...

de haan - flash me back, scotty

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