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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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Chapter 2: Building the Teradata RDBMS

Permanent Journals

Location of Change Images

Tables that include fallback and journaling options automatically receive dual image journal protection. Tables with no-fallback protection can request either single or dual permanent journals.

The placement of permanent journals depends on the:

Requested image type (either before or after)

Protection type (either fallback or no-fallback)

This type of AMP . . . Holds these types of images . . .
Primary AMP before- and/or after-image rows for any table with fallback protection. Holds single before images and dual after images for non-fallback protected tables.
Fallback AMP before- and/or after-image rows for tables with fallback protection. The system distributes duplicate data rows to fallback processors by assigning the row's hash code to a different AMP in the cluster.
Backup AMP single or dual after images and dual before images. Does not use a hashing algorithm for row distribution. All images for one AMP go to a single backup, which is always in the same cluster. For example, if AMPs 1, 2, 3, and 4 are in the same cluster, 1 backs up 2, 2 backs up 3, 3 backs up 4, and 4 backs up 1. There is no way to predict the backup AMP.

If fallback protection is too costly in terms of storage space, after-image journals offer alternative data protection with minimal space usage. After-image journals write changes to the backup AMP. Since the system only duplicates changed rows rather than all of the rows, storage space is minimized.

Since changes are written to the backup AMP, a primary AMP failure does not cause a loss of data. You can recover all table data by restoring the appropriate archive tape and rolling forward the rows stored in the after-image journal.

Creating or Deleting a Permanent Journal

Permanent journals are optional. You can specify journal options at the database/user level or at the individual table level.

You create a new permanent journal in the CREATE/MODIFY DATABASE/ USER definition. To create permanent journals within an existing user or database, use the MODIFY USER/DATABASE statement.

Unless you specify otherwise at the table level in the CREATE or ALTER TABLE definition, in each table created within that database or user space writes to that journal by default.

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Teradata RDBMS Database Administration Chapter 2: Building the Teradata RDBMS

Permanent Journals

You can associate an individual table in that database with a journal in a different database by specifying the fully qualified name of journal (in the form databasename.journaltablename) in the CREATE TABLE or ALTER TABLE statement.

Caution: If a database or user that contains a permanent journal runs out of space, all updates to tables that write to that journal will abort.

The following restrictions apply to the use of permanent journals:

If a journal table in another user/database is specified as the default, that other journal table must already exist.

You can change a DEFAULT JOURNAL for a user or database only if no tables or other databases journal into it.

Permanent journals are not supported across an AMP configuration change. Rollforward or rollback operations terminate if there is a change in the hash maps for primary, fallback, or backup rows.

Permanent journals are not supported across certain DDL statements. Statements that may prevent a rollforward or rollback operation from passing that point in the journal include:

ALTER TABLE (especially with REVALIDATE PRIMARY INDEX) |

RENAME TABLE

MODIFY USER or MODIFY DATABASE

COMMENT

Before you delete a journal, use the ALTER TABLE statement to stop journaling. Use MODIFY USER/DATABASE to remove the journal table.

Assigning a Permanent Journal

Users activate permanent journaling by including the JOURNAL option in the CREATE or MODIFY statements for users or databases. You must allocate sufficient permanent space to a database or user that will contain permanent journals.

Caution: If a database or user that contains a permanent journal runs out of space, all updates to tables that write to that journal will abort.

2 - 78 Teradata RDBMS Database Administration

Chapter 2: Building the Teradata RDBMS

Permanent Journals

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Teradata RDBMS Database Administration Chapter 3:

Space Considerations

This chapter shows you how to set disk space limits for your Teradata RDBMS and administer other aspects of your data space.

Topics discussed include:

Defining maximum limits for:

Permanent space

Temporary space

Spool space

Saving cylinders for PERM and SPOOL space |

Defining data block and free space limits

Monitoring disk space

Gaining space with PACKDISK

For more information on space issues and performance, including what to do if you start running out of disk space or free cylinders, see Teradata RDBMS Performance Optimization.
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