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Apr 18

Recovery Journal

TD Basics

by admin

The Teradata database uses Recovery Journal to automatically maintain data integrity in the case of :

An interrupted transaction

An AMP failure

Recovery Journals are created, maintained and purged by the system automatically, so no DBA interventionis required. Recovery journal are tables stored in the storage medium so they take up the disk space on thesystem.

There are three types of Recovery Journal in Teradata-

Transient Journal1.Down – AMP Recovery Journal2.Permanent Journal3.

very Journal » TeraData Tech http://www.teradatatech.com

5 11/16/2014 1



Now we look on each of the recovery journal in details –

Transient Journal

A transient journal maintains data integrity when in-flight transactions are interrupted. Data is returned to itsoriginal state after transaction failure.

A transient journal is used during normal system operation to keep “before images” of changed rows so thedata can be restored to its previous state if the transaction is not completed. This happens on each AMP aschanges occur. When a transaction is started, the system automatically stores a copy of all the rows affected by the transaction in the transient journal until the transaction is completed. Once the transaction is completed the “before images” are purged.

In the event of transaction failure, the “before images” are reapplied to the affected tables and deleted fromthe journal, and the “rollback” operation is completed.

Down AMP Recovery Journal

The down AMP recovery journal allows continued system operation while an AMP is down. A down AMPrecovery journal is used with fallback protected tables to maintain a record of write transactions (updates,creates, inserts, deletes, etc) on the failed AMP while it is unavailable.

The Down AMP recovery journal starts automatically after the loss of an AMP in a cluster. Any changes tothe data in the failed AMP are logged into the Down AMP recovery journal by the other AMPs in the cluster.When the failed AMP is brought back online, the restart process includes applying the changes in the Down – AMP recovery journal to the recovered AMP.

The journal is discarded once the process is complete, and the AMP is brought online, fully recovered.

Permanent Journal

Permanent Journals are an optional feature used to provide an additional level of data protection. You specifythe use of permanent journal at the table level. It provides full-table recovery to a specific point in time. Itcan also reduce the need for costly and time – consuming full table backups.

Permanent journals are tables stored on disk array like user data is, so they can take up additional disk space,on the system. The database administrator maintains the permanent journal entries (deleting, archiving, and so

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on).A database can have one permanent journal.

When you create a table with permanent journaling, you must specify whether the permanent journal willcapture.

Before images – for rollback to “undo” a set of changes to a previous state.After images – for roll forward to “redo” to a specific state.

Following is the syntax of giving permanent journal –

CREATE DATABASE teradatatechFROM space_amount ASPERM = 4000000 /* permanent space */ SPOOL = 2000000 /* spool space */ NO FALLBACK

ACCOUNT = ‘$admin’NO BEFORE JOURNALAFTER JOURNALDEFAULT JOURNAL TABLE = teradata.journal;Here Admin has opted for only AFTER JOURNAL and he has name the journal table as “teradata.journal”.When user creates a table in the database “teradatatech” , by default AFTER JOURNAL is available for himto protect his data when the hardware failure occurs.

He can opt for NO AFTER JOURNAL by overriding the default.

Scenario1 : Here by default the table has AFTER JOURNAL option.

CREATE TABLE table_name( field1 INTEGER,field2 INTEGER)PRIMARY INDEX field1;

Scenario2: in this case, user has specifically stated he wanted no AFTER JOURNAL for his data. This is howuser can override the defult.

CREATE TABLE table_nameFALLBACK,

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NO AFTER JOURNAL( field1 INTEGER,field2 INTEGER)PRIMARY INDEX field1;

In this case whenever the user inserts/updates and the transaction is committed , then the affected rows will be taken backup in the journal table “teradata.journal”

29 comments

No ping yet

admin says:

May 24, 2014 at 9:32 am (UTC 0)

Reply

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1.

Gopala says:

April 25, 2014 at 8:48 pm (UTC 0)

Reply

Admin

2.


5 11/16/2014 1



What is the use of Fallback, i think this also keeps the copy of table data if we have any failure or crashwith data is it?

admin says:

May 2, 2014 at 5:38 pm (UTC 0)

Reply

FALLBACK is used for data protection at table level.

1.

Moorthy says:

June 25, 2013 at 3:22 am (UTC 0)

Reply

Hi…. i have doubt in below mentioned point“The Down AMP recovery journal starts automatically after the loss of an AMP in a cluster. Anychanges to the data in the failed AMP are logged into the Down AMP recovery journal by the other AMPs in the cluster”

But Each AMP will have only access to it’s own disk right?But How other AMPs will bring any

changes in Other AMPS?

Can you clarify on this?

yavuz says:

January 23, 2014 at 1:22 pm (UTC 0)

Reply

Did you find the asnwer? I also really wonder how it happens..

1.

admin says:

January 23, 2014 at 2:02 pm (UTC 0)

2.

3.


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Reply

Down AMP Recovery journal pulls all modified data from fallback sector of each AMP. Anychanges to the base table is reflected in Fallback sector as well, so DARJ keeps on updating thismodified data.Once AMP is online, first task teradata will do is to update the base table with modified data of DARJ.

priyanki says:

March 27, 2013 at 8:25 pm (UTC 0)

Reply

This is the kind of crash course on TD i was looking for..Nice topic n a great Explanation…Thanks

4.

Nitin says:

October 9, 2012 at 5:45 am (UTC 0)

Reply

Thanks for sharing the info in such a simple manner.

5.

raag says:

May 31, 2012 at 3:57 pm (UTC 0)

Reply

Hi,

I have a question. if the no after journal is set in the second example, then how the affected data wil betaken backup in journal. i could not understand the difference between no after journal and after journal. can u please explain ?

6.

Prasath says:

7.


5 11/16/2014 1



April 27, 2012 at 7:09 am (UTC 0)

Reply

Concepts are suberbly explained. Thanks.

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September 23, 2011 at 3:00 pm (UTC 0)

Reply

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September 6, 2011 at 10:15 am (UTC 0)

Reply

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admin says:

September 7, 2011 at 11:11 am (UTC 0)

Reply

hiThere are lot of active RSS subscribers to my blog.

can u give more details regarding what kind of error your facing

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April 25, 2011 at 8:11 am (UTC 0)

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admin says:

April 25, 2011 at 8:12 am (UTC 0)

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