Flashback time travel vs Flash back Data Archive

1. ♨ Flashback time travel♨
vs
♨ Flash back Data Archive♨
Oracle 19c and newer
Sometimes DBA need to restore/recover important data set in production to avoiding data lost or
deletion by user interference, and human errors or any problems.
As examples consider a user did some wrong delete on a base table, at this situation if you alert
quickly you have a chance to
fl
ashback deleted rows on the table by using undo data, for
example:
SQL>insert into base_table
Select * from table1 AS OF TIMESTAMP TO_TIMESTAMP('224-02-12 13:34:12', 'YYYY-MM-DD
HH24:MI:SS');
Or
SQL>insert into base_table
Select * from table1 AS OF SCN 123456;
But this chance is depending on sizing of undo_retention parameter and undo tablespace.
that the UNDO_RETENTION is not guaranteed by default so the fact that the UNDO_RETENTION
is 900 seconds (=15 minutes) doesn't necessarily mean that you can query data as of 15 minutes
ago. Another thing that you should also take into account is the UNDO_RETENTION behaviour in
autoextend undo tabelspace vs.
fi
xed-size undo tablespace because in
fi
xed-size undo
tablespace the UNDO_RETENTION is being ignored by Oracle so it's basically meaningless
(unless retention guarantee is enabled).
So you can consider a bigger retention for your undo, but if you want to protect a big table in
production same as this way, this solution is not applicable (very large undo for recovering
inadvertent deleted data is not good solution)

2. Solution:
Use Flashback Data Archive (FDA).
This solution protects your speci
fi
c tables and also can be used for auditing and tracking
changes on the tables in a isolated and separated tablespace without need Undo tablespace!
So if we have big or very big tables also we can used this feature and we can enable or disable on
demand any time.
The FDA is available feom 11g but has some improvements on 19c and higher.
In Oracle 19c, they rebranded the feature called “Flashback Time Travel”. The Flashback Time
travel is a nothing but a combination Flashback Data archive and Flashback Query AS OF and
Versions.
Use Flashback Time Travel to automatically track and archive historical versions of changes to
tables enabled for
fl
ashback archive, ensuring SQL-level access to the versions of database
objects without getting a snapshot-too-old error.
The Historical data is key for business decisions and having reliable data is very important for
organizations. There are frequent implications for both
fi
nancial and legal data for organizations
and having a secure and accurate history of change of data is crucial for business. Oracle
Flashback technology o
ff
ers signi
fi
cant bene
fi
ts for database management and recovery to meet
the organizational needs.
Using Flashback Time Travel in Orcale 19c and higher
Flashback Time Travel provides the ability to track and store transactional changes to a table over
its lifetime. It is useful for compliance with record stage policies and audit reports.
A Flashback Archive consists of one or more tablespaces or parts thereof. You can have multiple
Flashback Archives. If you are logged on as SYSDBA, you can specify a default Flashback
Archive for the system. A Flashback Archive is con
fi
gured with retention time. Data archived in the
Flashback Archive is retained for the retention time speci
fi
ed when the Flashback Archive was
created.

3. Creating a Flashback Archive
You can create a Flashback Archive with the CREATEFLASHBACK ARCHIVE statement.
Create a Flashback Archive with the CREATEFLASHBACK ARCHIVE statement, specifying:
• Name of the Flashback Archive
• Name of the
fi
rst tablespace of the Flashback Archive
• (Optional) Maximum amount of space that the Flashback Archive can use in the
fi
rst tablespace
The default is unlimited. Unless your space quota on the
fi
rst tablespace is also unlimited, you
must specify this value; otherwise, error ORA-55621 occurs.
• Retention time (number of days that Flashback Archive data for the table is guaranteed to be
stored)
• (Optional) Whether to optimize the storage of data in the history tables maintained in the
Flashback Archive, using [NO]OPTIMIZE DATA.
The default is NO OPTIMIZE DATA.
If you are logged on as SYSDBA, you can also specify that this is the default Flashback Archive
for the system. If you omit this option, you can still make this Flashback Archive as default at a
later stage.
Oracle recommends that all users who must use Flashback Archive have unlimited quota on the
Flashback Archive tablespace; however, if this is not the case, you must grant su
ffi
cient quota on
that tablespace to those users.
Examples
• Create a default Flashback Archive named
fl
a1 that uses up to 10 G of tablespace tbs1, whose
data are retained for one year:
SQL> CREATE FLASHBACK ARCHIVE DEFAULT
fl
a1 TABLESPACE tbs1 QUOTA 10G
RETENTION 1 YEAR;
• Create a Flashback Archive named fa2 that uses tablespace tbs2, whose data are retained for
two years:
SQL> CREATE FLASHBACK ARCHIVE fa2 TABLESPACE tbs2 RETENTION 2 YEAR;
Examining and Restoring Past Data
By de
fi
ning FDA or FTT, retrieving data in a older time is same as Flashback method such as:
SQL> Select * from table1 AS OF TIMESTAMP TO_TIMESTAMP('2024-02-12 13:30:12', 'YYYY-
MM-DD HH24:MI:SS');
Suppose that you discover at 12:30 PM that the row for employee KAMRANI was deleted from
the employees table, and you know that at 9:30AM the data for KAMRANI was correctly stored in
the database. You can use Oracle Flashback Query to examine the contents of the table at 9:30
AM to
fi
nd out what data was lost. If appropriate, you can restore the lost data.
Example 1:
Retrieves the state of the record for Kamrani at 9:30AM, April 4, 2024:
SELECT * FROM employees
AS OF TIMESTAMP
TO_TIMESTAMP('2024-02-04 09:30:00', 'YYYY-MM-DD HH:MI:SS')
WHERE last_name = 'Kamrani ';
Example 2 Restores Kamrani's information to the employees table:

4. INSERT INTO employees (
SELECT * FROM employees
AS OF TIMESTAMP
TO_TIMESTAMP('2024-02-04 09:30:00', 'YYYY-MM-DD HH:MI:SS')
WHERE last_name = 'Kamrani'
);
Bene
fi
ts of Flashback data archive:
Uses of Oracle Flashback Query include:
• Recovering lost data or undoing incorrect, committed changes.
For example, if you mistakenly delete or update rows, and then commit them, you can
immediately undo the mistake.
• Comparing current data with the corresponding data at an earlier time.
For example, you can run a daily report that shows the change in data from yesterday. You can
compare individual rows of table data or
fi
nd intersections or unions of sets of rows.
• Checking the state of transactional data at a particular time.
For example, you can verify the account balance of a certain day.
• Selecting data that was valid at a particular time or at any time within a user-de
fi
ned valid time
period.
For example, you can
fi
nd employees with valid employee information as of a particular
timestamp or between a speci
fi
ed start and end time in the speci
fi
ed valid time period.
• Simplifying application design by removing the need to store some kinds of temporal data.
Oracle Flashback Query lets you retrieve past data directly from the database.
• Applying packaged applications, such as report generation tools, to past data.
• Providing self-service error correction for an application, thereby enabling users to undo and
correct their errors.
Guidelines for Oracle Flashback Query
• You can specify or omit the AS OF clause for each table and specify di
ff
erent times for di
ff
erent
tables.
• Note: If a table is a Flashback Time Travel and you specify a time for it that is earlier than its
creation time, the query returns zero rows for that table, rather than causing an error.
• You can use the AS OF clause in queries to perform data de
fi
nition language (DDL) operations
(such as creating and truncating tables) or data manipulation language (DML) statements (such
as INSERT and DELETE) in the same session as Oracle Flashback Query.
• To use the result of Oracle Flashback Query in a DDL or DML statement that a
ff
ects the current
state of the database, use an AS OFclause inside an INSERT or CREATE TABLEAS SELECT
statement.
• If a possible 3-second error (maximum) is important to Oracle Flashback Query in your
application, use an SCN instead of a time stamp.
• You can create a view that refers to past data by using the AS OF clause in the SELECT
statement that de
fi
nes the view.
If you specify a relative time by subtracting from the current time on the database host, the past
time is recalculated for each query. For example:
CREATE VIEW hour_ago AS SELECT * FROM employees AS OF TIMESTAMP
(SYSTIMESTAMP - INTERVAL '60' MINUTE);
SYSTIMESTAMP refers to the time zone of the database host environment.
• You can use the AS OF clause in self-joins, or in set operations such as INTERSECTand MINUS,
to extract or compare data from two di
ff
erent times.
You can store the results by preceding Oracle Flashback Query with a CREATETABLE AS
SELECT or INSERT INTO TABLESELECT statement. For example, this query reinserts into table
employees the rows that existed an hour ago:
INSERT INTO employees (SELECT * FROM employees AS OF TIMESTAMP
(SYSTIMESTAMP - INTERVAL '60' MINUTE) MINUS SELECT * FROM employees;

5. SYSTIMESTAMP refers to the time zone of the database host environment.
• You can use the AS OF clause in queries to check for data that was valid at a particular time.
Using Oracle Flashback Version Query
Use Oracle Flashback Version Query to retrieve the di
ff
erent versions of speci
fi
c rows that existed
during a given time interval. A row version is created whenever a COMMIT statement is executed.
Note:After executing a CREATE TABLE statement, wait at least 15 seconds to commit any
transactions, to ensure that Oracle Flashback Version Query re
fl
ects those transactions.
Specify Oracle Flashback Version Query using the VERSIONS BETWEEN clause of the SELECT
statement. The syntax is either:
VERSIONS BETWEEN { SCN | TIMESTAMP } start AND end
where start and end are expressions representing the start and end, respectively, of the time
interval to be queried. The time interval includes (start and end).
or:
VERSIONS PERIOD FOR user_valid_time [ BETWEEN TIMESTAMP start AND end ]
where user_valid_time refers to the user-speci
fi
ed valid time period.
Oracle Flashback Version Query returns a table with a row for each version of the row that existed
at any time during the speci
fi
ed time interval. Each row in the table includes pseudocolumns of
metadata about the row version, which can reveal when and how a particular change (perhaps
erroneous) occurred to your database.
For example, this output indicates that the salary was 10243 from September 9, 2023, included,
to November 25, 2024, excluded.
VERSIONS_START_TIME VERSIONS_END_TIME SALARY
----------------- ----------------- ------
09-SEP-2"24 25-NOV-2024 10243
Here is a typical use of Oracle Flashback Version Query:
SELECT versions_startscn, versions_starttime,
versions_endscn, versions_endtime,
versions_xid, versions_operation,
last_name, salary
FROM employees
VERSIONS BETWEEN TIMESTAMP
TO_TIMESTAMP('2024-12-18 14:00:00', 'YYYY-MM-DD HH24:MI:SS')
AND TO_TIMESTAMP('2024-12-18 17:00:00', 'YYYY-MM-DD HH24:MI:SS')
WHERE
fi
rst_name = 'John';
You can use VERSIONS_XID with Oracle Flashback Transaction Query to locate this transaction's
metadata, including the SQL required to undo the row change and the user responsible for the
change.
Flashback Version Query allows index-only access only with IOTs (index-organized tables), but
index fast full scan is not allowed.
Using Flashback Time Travel
Flashback Time Travel provides the ability to track and store transactional changes to a table over
its lifetime. It is useful for compliance with record stage policies and audit reports.

6. A Flashback Archive consists of one or more tablespaces or parts thereof. You can have multiple
Flashback Archives. If you are logged on as SYSDBA, you can specify a default Flashback
Archive for the system. A Flashback Archive is con
fi
gured with retention time. Data archived in the
Flashback Archive is retained for the retention time speci
fi
ed when the Flashback Archive was
created.
By default, Flashback Archive is not enabled for any tables. You can enable Flashback Archive for
a table if all of these conditions are true:
• You have the FLASHBACK ARCHIVE object privilege on the Flashback Archive to use for that
table.
• The table is not nested, temporary, remote, or external.
• The table contains neither LONG nor nested columns.
• The table does not use any of these Flashback Archive reserved words as column names:
◦ STARTSCN
◦ ENDSCN
◦ RID
◦ XID
◦ OP
◦ OPERATION
You cannot enable Flashback Archive on a nested table, temporary table, external table,
materialized view, Advanced Query (AQ) table, or non-table object.
After Flashback Archive is enabled for a table, you can disable it only if you either have the
FLASHBACKARCHIVE ADMINISTER system privilege or you are logged on as SYSDBA.
When choosing a Flashback Archive for a speci
fi
c table, consider the data retention requirements
for the table and the retention times of the Flashback Archives on which you have the
FLASHBACK ARCHIVEobject privilege.
E
ff
ective with Oracle Database 12c Release 1 (12.1.0.1), Flashback Archive is enhanced to include
the following:
• User context tracking. The metadata information for tracking transactions can include (if the
feature is enabled) the user context, which makes it easier to determine which user made which
changes to a table.
To set the user context level (determining how much user context is to be saved), use the
DBMS_FLASHBACK_ARCHIVE.SET_CONTEXT_LEVEL procedure. To access the context
information, use the DBMS_FLASHBACK_ARCHIVE.GET_SYS_CONTEXT function.
• Database hardening. This feature enables you to associate a set of tables together in an
"application", and then enable Flashback Archive on all those tables with a single command.
Also, database hardening enables you to lock all the tables with a single command, preventing
any DML on those tables until they are subsequently unlocked. Database hardening is designed
to make it easier to use Flashback Time Travel to track and protect the security-sensitive tables
for an application.
DDL Statements on Tables Enabled for Flashback Archive
Flashback Archive supports only these DDL statements:
• ALTER TABLE statement that does any of the following:
◦ Adds, drops, renames, or modi
fi
es a column
◦ Adds, drops, or renames a constraint
◦ Drops or truncates a partition or subpartition operation
• TRUNCATE TABLE statement
• RENAME statement that renames a table
Flashback Archive does not support DDL statements that move, split, merge, or coalesce
partitions or subpartitions, move tables, or convert LONG columns to LOB columns.
For example, the following DDL statements cause error ORA-55610 when used on a table
enabled for Flashback Archive:
• ALTER TABLE statement that includes an UPGRADE TABLE clause, with or without an
INCLUDING DATA clause
• ALTER TABLE statement that moves or exchanges a partition or subpartition operation
• DROP TABLE statement
If you must use unsupported DDL statements on a table enabled for Flashback Archive, use the
DBMS_FLASHBACK_ARCHIVE.DISASSOCIATE_FBAprocedure to disassociate the base table
from its Flashback Archive. To reassociate the Flashback Archive with the base table afterward,

7. use the DBMS_FLASHBACK_ARCHIVE.REASSOCIATE_FBAprocedure. Also, to drop a table
enabled for Flashback Archive, you must
fi
rst disable Flashback Archive on the table by using the
ALTER TABLE ... NO FLASHBACK ARCHIVE clause.
Consideration:
Before con
fi
guration of FDA you should consider following:
Allocate su
ffi
cient storage to handle retention period
•For Faster access create indexes on the History tables
•Ideal approach is to create FDA on tables with primary key
•Enable FDA on tables which are important for business not on all tables in a schema
Limitations:
You can enable
fl
ashback data archive, but you must meet below conditions:
You cannot enable Flashback Archive on a nested table, temporary table, external table,
materialized view, Advanced Query (AQ) table, or non-table object.
•The table is not nested, remote, external, or temporary
•The table has neither nested column or LONG column
•The table does not any reserved words as column names such as START SCN, END SCN, OP,
OPERATION, XID, RID
•The user should have FLASHBACK ARCHIVE object privilege.
Conclusion:
The historical data is key for business decisions and having reliable data is very important for
organizations. Flashback Data Archive and Time Travel provides centralized historical data store
by tracking changes in a secure and e
ffi
cient way, which helps organization with compliance,
audit, historical reporting, selective data recovery and restore lost data cause of human
interference
and many other capabilities, but this feature have some limitations aslo.
For more information see:
https://docs.oracle.com/en/database/oracle/oracle-database/19/adfns/
fl
ashback.html
Sincerely,
Alireza Kamrani.