Lesson 11 Fb Queries

8/12/2019 Lesson 11 Fb Queries

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Copyright 2007, Oracle. All rights reserved.

Using Flashback Technology


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Copyright 2007, Oracle. All rights reserved.11 - 2

Objectives

After completing this lesson, you should be able to: Query the recycle bin

Restore dropped tables from the recycle bin

Perform Flashback Query

Use Flashback Version Query

Use Flashback Transaction Query

Use Flashback Transaction


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Flashback Technology

ObjectLevel Scenario Examples FlashbackTechnology DependsOn AffectsData

Database Truncate table; Undesired

multitable changes made

Database Flashback

logs

TRUE

Table Drop table Drop Recycle bin TRUE

Update with the wrongWHEREclause

Table Undo data TRUE

Compare current data

with data from the past

Query Undo data FALSE

Compare versions of a

row

Version Undo data FALSE

Keep historical

transaction data

Data Archive Undo data TRUE

Transaction Investigate and back out

suspect transactions

Transaction Undo data TRUE


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Transactions and Undo

Undo old data

in undo tablespace

DML operations

Original data

in

buffer cache


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Guaranteeing Undo Retention

A transaction that generates

more undo than what there

is space for will fail.

SELECTstatements

running 15 minutes or less

are always satisfied.

Undo data in

undo

tablespace

Retention guarantee:

15 minutes


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Preparing Your Database for Flashback

Creating an undo tablespace Enabling Automatic Undo Management

Specifying versus guaranteeing undo retention

Default database initialization parameters:UNDO_MANAGEMENT='AUTO'

UNDO_TABLESPACE='UNDOTBS1'

UNDO_RETENTION=900


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Flashback Drop and the Recycle Bin

DROP TABLE employees; FLASHBACK TABLEemployeesTO BEFORE DROP;

Mistake wasmade.

RECYCLEBIN=ON



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21

Recycle Bin

DROP TABLE employees;

BIN$zbjra9wy==$0EMPLOYEES_PK

EMPLOYEES

Recycle

bin

DBA_FREE_SPACEBIN$zbjrBdpw==$0

USER_OBJECTS

BIN$zbjrBdpw==$0 EMPLOYEESBIN$zbjra9wy==$0 EMPLOYEES_PK

4

Objects are:

Renamed

Not moved



Restoring Tables from the Recycle Bin

Restore dropped tables and dependent objects. If multiple recycle bin entries have the same original name:

Use unique, system-generated names to restore a particular

version

When using original names, the restored table is last in, firstout (LIFO)

Rename the original name if that name is currently used.

FLASHBACK TABLE TO BEFORE DROP[RENAME TO ];



Recycle Bin: Automatic

Space Reclamation

BIN$zbjrBdpw==$0BIN$zbjra9wy==$0

BIN$zbjra9wy==$0

BIN$zbjrBdpw==$0

1

2

3

Recycle bin

DBA_FREE_SPACE - RECYCLEBIN

Autoextend



Recycle Bin: Manual Space Reclamation

PURGE {TABLE |INDEX }

PURGE TABLESPACE [USER ]

PURGE [USER_|DBA_]RECYCLEBIN


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Querying the Recycle Bin

SELECT owner, original_name, object_name,type, ts_name, droptime, related, space

FROM dba_recyclebinWHERE can_undrop = 'YES';

SQL> SELECT original_name, object_name, ts_name, droptimeFROM user_recyclebin WHERE can_undrop = 'YES'; 2

ORIGINAL_NAME OBJECT_NAME TS_NAM DROPTIME------------- ----------------------- ------ -------------------EMPLOYEES2 BIN$NE4Rk64w...gbpQ==$0 USERS 2007-07-02:15:45:13

SQL> SHOW RECYCLEBIN



Querying Data from

Dropped Tables

SELECT ...FROM "BIN$zbjrBdpw==$0" [AS OF ...]WHERE ...

Recycle

bin

DBA_INDEXES

YES

INDEX_NAMEDROPPED

NO SALES_PK

DBA_TABLES

TABLE_NAMEDROPPED

YES

NO SALES

BIN$zbjrBdpw==$0 EMPLOYEES

BIN$zbjra9wy==$0 EMPLOYEES_PK



Using Flashback Technology to Query Data

Flashback Query Query all data at a specified point in time.

Flashback Version Query

See all versions of a row between two times.

See the transactions that changed the row. Flashback Transaction Query

See all changes made

by a transaction.

Tx3

Tx1

Tx2

Time

Flashback



Flashback Query

T1 T2

SELECT employee_id, salary FROM employees

AS OF TIMESTAMP

WHERE employee_id = 200

employeesemployees Unwantedupdates

Use to query all data at a specified point in time.



Flashback Query: Example

11:00 11:10

UPDATE employeesSET salary =

(SELECT salary FROM employeesAS OF TIMESTAMP TO_TIMESTAMP('2005-05-0411:00:00','yyyy-mm-ddhh24:mi:ss')WHERE employee_id = 200)

WHERE employee_id = 200

employeesemployees

salary = 4,400

employees

salary = 4,400salary = 4,840




t1 t2

Tx1 Tx2

SELECT versions_xid, salary FROM employees

VERSIONS BETWEEN TIMESTAMP and

WHERE employee_id = 200;

Tx0

Tx0 Tx1 Tx2

employees employeesemployees

200



Using Enterprise Manager to Perform




Flashback Version Query:

Considerations

The VERSIONSclause cannot be used to query: External tables

Temporary tables

Fixed tables

Views The VERSIONSclause cannot span DDL commands.

Segment shrink operations are filtered out.



Flashback Transaction Query

Undo

SQL

FLASHBACK_TRANSACTION_QUERY

DBA

User

Erroneous

DML



Using Enterprise Manager to Perform

Flashback Transaction Query



Flashback Transaction Query:

Considerations

DDL commands are seen as dictionary updates. Flashback Transaction Query on a transaction underlying a

DDL command displays the data dictionary changes.

Dropped objects appear as object numbers.

Dropped users appear as user identifiers.



Flashback Transaction

Setting up Flashback Transaction prerequisites Stepping through a possible workflow

Using the Flashback Transaction Wizard

Querying transactions with and without dependencies

Choosing back-out options and flashing back transactions Reviewing the results


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Prerequisites


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Possible Workflow

1. Viewing data in a table2. Discovering a logical problem

3. Using Flashback Transaction

1. Performing a query

2. Selecting a transaction3. Flashing back a transaction (with no conflicts)

4. Choosing other back-out options (if conflicts exists)

4. Reviewing Flashback Transaction results


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Viewing Data


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Flashback Transaction Wizard


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Choosing Other Back-out Options


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Final Steps Without EM

After choosing your back-out option, the dependency report isgenerated in the DBA_FLASHBACK_TXN_STATEand

DBA_FLASHBACK_TXN_REPORTtables.

Review the dependency report that shows all transactions

which were backed out.

Commit the changes to make them permanent.

Roll back to discard the changes.


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Lesson 11 Fb Queries