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Introduction to the Teradata® RDBMS for UNIX® Version 2 Release 2.1 - NCR

NCR Introduction to the Teradata® RDBMS for UNIX® Version 2 Release 2.1 - NCR, 1998. - 315 p.
Download (direct link): inntroduktionteradata1998.pdf
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FG10A001

Note that the fallback copy of any row is always located on a different AMP from the primary copy. This is an entry level fault tolerance strategy. The data on AMP3 is fallback-protected on AMPs 4, 5, and 6. If AMP 3 were to fail, the data would still be available on the other AMPS. If AMPs 3 and 6 were to fail at the same time, however, the system would become unavailable.

9-4

Introduction to the Teradata RDBMS for UNIX
Figure 9-3

Clustered AMPs With Fallback

Fault Tolerance

Software Fault Tolerance

The next picture illustrates a way around this problem—clustering.

AMP1

AMP2

AMP3

Cluster A

AMP4

Primary copy area 1,9,17 2,10,18 3,11,19 4,12,20
Fallback copy area 2,3,4 1,11,12 9,10,20 17,18,19

AMP5

Cluster B

AMP6

AMP7

AMP8

Primary copy area 5,13,21 6,14,22 7,15,23 8,16,24
Fallback copy area 6,7,8 5,15,16 13,14,24 21,22,23

The illustration shows the same eight AMP configuration which has been partitioned into two AMP clusters of four AMPs each.

A cluster is a group of from two to sixteen AMPs in which each primary row in the cluster is fallback-protected on another AMP in the same cluster.

Compare this clustered configuration with the earlier illustration of an unclustered AMP configuration. In the example, the (primary) data on AMP 3 is backed up on AMPs 0, 1, and 2 and the data on AMP 6 is backed up on AMPs 4, 5, and 7.

If AMPs 3 and 6 were to fail at the same time, the system would continue to function normally. Only if two failures occurred within the same cluster would the system halt.

The primary issue determining cluster size is performance. While two-AMP clusters provide maximum protection against system loss (because the likelihood of both AMPs in a cluster going down simultaneously is vanishingly small), this configuration also suffers from a higher workload per AMP in the event of a failure.

A rule of thumb to follow is to create AMP clusters of 4 AMPs each. This configuration maximizes the tradeoff between the probability of a failure and performance degradation.

FG10A002

Introduction to the Teradata RDBMS for UNIX

9-5
Fault Tolerance

Software Fault Tolerance

Journaling

The Teradata RDBMS permits several different kinds of journaling. Some are done by the system and others are user-specified.

The following table explains the different journaling capabilities of the Teradata RDBMS.

Journal Type Description Maintained By
Down AMP recovery journal • Active during an AMP failure only. • Journals fallback tables only. • Discarded after the down AMP recovers. System (automatic)
Transient journal • Logs BEFORE images for all transactions. • Used by system to roll back failed transactions aborted either by the user or by the system. • Captures: • BT/ET images for all transactions. • Before images for updates and deletes. • Row IDs for inserts. • Control records for creates and drops. • Each image is kept on the same AMP as the row it describes. • Images are discarded when the transaction or rollback completes. System (automatic)
Permanent journal • Active continuously. • Available for tables or databases. • Provides rollforward for hardware failure recovery. • Provides rollback for software failure recovery. • Provides full recovery of nonfallback tables. • Reduces need for frequent full table archives. User (optional)

9-6

Introduction to the Teradata RDBMS for UNIX
Fault Tolerance

Tape Archive and Restore/Recovery Utilities

Tape Archive and Restore/Recovery Utilities

This topic describes using the Archive and Restore/Recovery and Introduction ASF2 utilities to copy and restore or recover a table or database.

The Archive and Restore/Recovery utility backs up data to an IBM channel-attached client, while the ASF2 utility performs a local backup or a backup to a network-attached client.

An archive operation is one in which you use the utility to copy Archiving Data 9 selected or all tables or databases from your Teradata RDBMS.

You should archive your Data Dictionary immediately after you archive your data.

If your system is used only for decision support and is updated regularly with data loads, you might not want to archive the data. Consult your DBA or system programmer about the advisability of not making regular archives of your databases.

Restoring is distinct from recovering.

Restoring Data 9

In a restore operation, you are copying an archive from the client or server back to the database.

You can restore data to all AMPs, to clusters of AMPs, or to a specific AMP as long as the data dictionary contains the definitions of the table or database you want to restore.

If the table does not have a definition in the data dictionary because of a DROP or RENAME statement, you can still restore data using the COPY statement.

Recovering is distinct from restoring.

Recovering Data 9

In a recovery operation, you are applying before or after journal images using a ROLLBACK or ROLLFORWARD statement.
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