A Teradata Database Teradata

Within Teradata, a database is a storage location for database objects (tables, views, macros, and triggers). An administrator can use Data Definition Language (DDL) to establish a database by using a CREATE DATABASE command.

A database may have PERMANENT (PERM) space allocated to it. This PERM space establishes the maximum amount of disk space for storing user data rows in any table located in the database. However, if no tables are stored within a database, it is not required to have PERM space. Although a database without PERM space cannot store tables, it can store views and macros because they are physically stored in the Data Dictionary (DD) PERM space and require no user storage space. The DD is in a "database" called DBC.

Teradata allocates PERM space to tables, up to the maximum, as rows are inserted. The space is not pre-allocated. Instead, it is allocated, as rows are stored in blocks on disk. The maximum block size is defined either at a system level in the DBS Control Record, at the database level or individually for each table. Like PERM, the block size is a maximum size. Yet, it is only a maximum for blocks that contain multiple rows. By nature, the blocks are variable in length. So, disk space is not pre-allocated; instead, it is allocated on an as needed basis, one sector (512 bytes) at a time. Therefore, the largest possible wasted disk space in a block is 511 bytes.

A database can also have SPOOL space associated with it. All users who run queries need workspace at some point in time. This SPOOL space is workspace used for the temporary storage of rows during the execution of user SQL statements. Like PERM space, SPOOL is defined as a maximum amount that can be used within a database or by a user. Since PERM is not pre-allocated, unused PERM space is automatically available for use as SPOOL. This maximizes the disk space throughout the system.

It is a common practice in Teradata to have some databases with PERM space that contain only tables. Then, other databases contain only views. These view databases require no PERM space and are the only databases that users have privileges to access. The views in these databases control all access to the real tables in other databases. They insulate the actual tables from user access. There will be more on views later in this book.

The newest type of space allocation within Teradata is TEMPORARY (TEMP) space. A database may or may not have TEMP space, however, it is required if Global Temporary Tables are used. The use of temporary tables is also covered in more detail later in the SQL portion of this book.

A database is defined using a series of parameter values at creation time. The majority of the parameters can easily be changed after a database has been created using the MODIFY DATABASE command. However, when attempting to increase PERM or TEMP space maximums, there must be sufficient disk space available even though it is not immediately allocated. There may not be more PERM space defined that actual disk on the system. A number of additional database parameters are listed below along with the user parameters. These parameters are tools for the database administrator and other experienced users when establishing databases for tables and views.



Face Book Twitter Google Plus Instagram Youtube Linkedin Myspace Pinterest Soundcloud Wikipedia

All rights reserved © 2018 Wisdom IT Services India Pvt. Ltd DMCA.com Protection Status

Teradata Topics