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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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Fallback Versus PJ

PJ is not a substitute for fallback or RAID. The difference can be summarized as follows:

Fallback and RAID maintain a duplicate copy of the current image of every row in the data table.

The PJ maintains before and/or after image rows that the system uses to roll table data forward or backward in time.

Space Allocation

A PJ requires permanent space. The system uses fallback hash maps to determine the fallback AMP for the journal row. A fallback AMP is another AMP in the same cluster.

A backup AMP is another AMP in the same cluster as the primary AMP. The system does not use a hashing algorithm for backup AMPs. All images for one AMP go to a single backup in the same cluster.

For more information on PJ options, see the CREATE DATABASE/ CREATE USER/CREATE TABLE statements, and the MODIFY DATABASE/MODIFY USER/ALTER TABLE statements in Teradata RDBMS SQL Reference.

PJs have the following effects on recovery from a single disk failure:

Protection Notes
Fallback tables, dual image journals Data is fully available. Journals play no part in recovery.
No fallback tables, dual image journals Data is partially available. You may fully recover data and journals.
No fallback tables, single image journals Data is partially available. You may recover data, but the journals are lost.
No fallback tables, no journals Data is partially available. You can recover data only to the point of the last archive.
RAID 5 or RAID The system may perform fallback less often, so you may need PJs.

7 - 38 Teradata RDBMS Database Administration

Chapter 7: Protecting Data

Permanent Journal (PJ) Protection

Deleting a PJ

You might want to delete a PJ if no table has been assigned to use that journal, or if you chose to use another PJ for administrative reasons.

However, be very cautious that no data tables are still defined to write to that journal when you delete it.

An archive of your database cannot be restored if it contains tables defined to write to a journal table that does not exist in the archive.

To delete a PJ:

Step Action
1 Submit an ALTER TABLE statement to stop the journaling to that PJ:
ALTER TABLE table name
WITH JOURNAL TABLE = journal table name
,NO BEFORE JOURNAL
,NO AFTER JOURNAL;
2 Submit a MODIFY DATABASE/MODIFY USER statement. For example: MODIFY DATABASE database_name AS DROP DEFAULT JOURNAL TABLE = journal_table_name;

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Teradata RDBMS Database Administration Chapter 7: Protecting Data

Guidelines for Choosing Data Protection

Guidelines for Choosing Data Protection

When selecting which data protection to use, consider the following guidelines:

IF ... THEN .
you require high data availability disk space is not a concern use fallback
all data maintenance is performed on the client, and the Teradata RDBMS is downloaded for query only tables can be reloaded from the client in case of failure data availability is of secondary importance disk space is a major consideration do not use fallback do not use PJ
the table is not fallback-protected, and data maintenance is performed on the Teradata RDBMS you require the ability to back out committed changes to a specific time large production tables must be archived while production continues use PJ

The following table summarizes the advantages and disadvantages of data protection alternatives.

Protection Mode Advantages Disadvantages
Fallback Transparent Requires no manual intervention. Data is fully available after a failure. Requires twice as much disk space. Requires twice as many write I/O operations as only using PJ. Requires more than twice as much processing time to update (insert, update, and delete) rows. CPU utilization may increase 20% to 40% using fallback.
No fallback Requires less disk space. Requires fewer I/Os. Data not fully available after a failure. Requires reloading if a failure occurs.
PJ No writes to the TJ are required for PJ images. A single-image journal is as fast, or faster, than fallback without PJ. Requires less disk space (if properly managed). Requires human intervention. Dual image journaling is slower than fallback.

Teradata RDBMS Database Administration

7 - 41 Chapter 7: Protecting Data

Crashdumps and Fallback Protection

Crashdumps and Fallback Protection

DIP creates the Crashdumps database with the FALLBACK protection option. Thus, because tables default to the same protection defined for the database in which they reside, PDE dumps are saved as fallback tables.

Accessing Dump Data

The FALLBACK option enables dumps to be saved in the database when an AMP is down.

This means that even if the Teradata RDBMS cannot come up with all vprocs, you can still access current dump data with the client-resident Dump Load/Unload (DUL) utility to find the cause of the problem. (For DUl utility usage information, refer to Teradata RDBMS Utilities)
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