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Teradata RDBMS Database Administration - NCR

NCR Teradata RDBMS Database Administration - NCR , 2004. - 616 p.
Download (direct link): teradatadatabaseadmin2004.pdf
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7 - 32 Teradata RDBMS Database Administration

Chapter 7: Protecting Data

AMP Clustering and Fallback

Spanning Clusters Across Cliques

It is desirable, when possible, to assign AMPs from different cliques to a cluster. Having each AMP in a separate clique improves the likelihood that data will remain available in the event a failure affects an entire clique.

Although such a failure is far less likely in a large configuration than the failure of a single node, a clique failure could have a serious impact. This is illustrated by the example clusters of two possible configurations (A and B) below.

Clusters, Configuration A

1 2 3 4 . . 8
--- --- --- --- ---
AMP IDs in 1-0 1-1 1-2 1-3 . . 1-7
2-0 2-1 2-2 2-3 . . 2-7
Cluster 3-0 3-1 3-2 3-3 . . 3-7
4-0 4-1 4-2 4-3 . . 4-7

Clusters, Configuration B

1 2 3 4 .. . 8
--- --- --- --- ---
AMP IDs in 1-0 1-4 2-0 2-4 . . 4-4
1-1 1-5 2-1 2-5 . . 4-5
Cluster 1-2 1-6 2-2 2-6 . . 4-6
1-3 1-7 2-3 2-7 . . 4-7

In this example, assume that each configuration has 4 cliques, each containing 8 AMPs, with 8 clusters of 4 AMPs each. Each AMP in each cluster is identified by a unique vprocid. Vprocids are shown in the format c-p (clique number-vprocid) to better illustrate the issue. The actual format is nnnn, where a vprocid is in the range 0-1023.

In configuration A, AMPs in each cluster are spread across cabinets; therefore, failure of a cabinet results in the loss of just a single AMP in each cluster. If there are no other processor failures, the system continues to run because primary data for AMPs in the failed cabinet remains available on the fallback AMPs in the other cabinets.

In configuration B, failure of a cabinet results in the loss of all AMPs in two clusters. This causes the entire system to fail because primary and fallback data is unavailable for two clusters.

7 - 32

Teradata RDBMS Database Administration Chapter 7: Protecting Data

AMP Clustering and Fallback

Spanning Clusters Across Arrays

For multi-clique configurations, you can define clusters so that each AMP in a cluster comes from a different clique. This grouping of clusters protects all your data rows, even if an entire clique should fail.

In this case, the cluster size can be no larger than the total number of cliques.

Archiving by Cluster

The Archive/Recovery (ARC) utility allows backup and restore of data from clustered AMPs. A CLUSTER option is available on both the DUMP and the RESTORE commands. For more information on ARC, see Chapter 8: "Archiving, Restoring and Recovering Data" and Teradata Archive/Recovery Utility Reference. I

Because non-local PJs enable data to be rolled forward after tables are restored, the JOURNAL option (in the CREATE USER/DATABASE/TABLE statement) is recommended if you decide to define clusters.

The following section explains the advantages of permanent journaling.

7 - 32 Teradata RDBMS Database Administration

Chapter 7: Protecting Data

Permanent Journal (PJ) Protection

Permanent Journal (PJ) Protection

A Permanent Journal (PJ) stores an image of each data row that has been changed with an INSERT, UPDATE, or DELETE statement. PJ images can reflect row values as they appeared before the change, after the change, or both. A database/user can contain only one PJ.

PJ rows are under your control, so you can checkpoint, archive, and restore them. PJs remain available until you delete them. PJ tables provide protection against:

Loss of data caused by a disk failure in a table that is not fallback- or RAID-protected

Loss of data if two or more AMPs fail in the same cluster (that is, loss of two disks in a rank/failed AMP)

Incorrect operation of a batch or application program

Loss of changes made after a data table is archived

With dual journaling, loss of one copy of the journal table

PJ also allows disaster recovery of an entire system.

PJ Options

A PJ provides the following options:

Option Description Change Image Location
Fallback Tables Non-Fallback Tables
Single before-image Captures image before a data row change Provides protection against software failure Allows rollback to a checkpoint Primary AMP and fallback AMP Primary AMP
Single afterimage Captures image after a data row change Provides protection against hardware failure Allows rollforward to a checkpoint Primary AMP and fallback AMP Backup AMP
Dual before-image Maintains two copies of an image before a data row change Provides protection against journal loss Primary AMP and backup AMP
Dual afterimage Maintains two copies of an image after a data row change Provides protection against journal loss Primary AMP and backup AMP

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Teradata RDBMS Database Administration Chapter 7: Protecting Data

Permanent Journal (PJ) Protection

Journaling of Fallback Tables

If you specify PJ for a table with fallback, the journal rows are also fallback-protected. That is, regardless of the type of journaling selected, each journal row is always written to both the primary disk and the corresponding fallback disk.
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