TeraData Basics

5-Jun-2011
[Following things have been copied from Teradata Datbase Administration manual which is available on net]

Overview of Space

Permanent : Perm space allocated to a user or database is a uniquely defined, logical repository for
1. Data Tables
2. Table Hearders (2 header rows per table)
3. Secondary Indexes (SI) [Primary Indexes are part of the table]
4. Join Indexes (JI)
5. Hash Indexes (HI)
6. Permanent Journals
7. Stored Procedures
8. Triggers
9. User Defined Functions (UDF)
10. User Defined Methods (UDM)

When an object is created or data rows are inserted, the space is allocated as needed from the perm space of the immediate owner. The space is returned automatically when no longer needed.

Note: The space allocated to a user or database that is un-assigned to an object is available for spool or temp space.

A database or user with no perm space can still own views, macros, and triggers but can not have objects that require space such as tables, UDFs, stored procedures, HIs, JIs, or journals.

Spool: Spool space holds intermediate query results or formatted answer sets to queries and volatile tables. The system can use unassigned per space for spool space.

When a user creates a new users or databases, the amount of spool space for those new objects must not exceed the spool space limit of their immediate owner. If you do not specify a spool space limit, a new user automatically inherits the same amount of spool as its parent.

To more easily manage spool space, define the value for spool in a profile. You can then assign a profile to users and all of the users will inherit the spool space definition.

Temporary (Temp) : Temp space defines the number of bytes the system will user to store data for global temporary tables. The value you specify must not exceed the value of the immediate parent at the time of creation. If you do not specify a value, the maximum vgalue defaults to that of the parent.

To more easily manage temp spcae, define the value for it in a profile. You can then assign a group of users to this profile and all of the users will inherit thje tmep space definition.



Permanent Space Availability
Initially, all available permanent space in the system is allocated to user DBC. From user DBC, you create other users who use up some of the space owned by DBC. As you create additional new databases, or users under those users, permanent space limits are deducted from the available (unused) space of the immediate owner of that database or user. If those users use up all the space allocated to them by their owner, those users can not create new objects untill they obtain more space.

Note : Unused space is allocated dynamically for temporary or spool space, which can reduce the actual amount of perm space available at a given point in time. Thus, specifying a PERM limit does not guarantee that a session can get all of that space upon demand.

To determine the amount of perm space available by a per-AMP basis, query the DBC.DiskSpace view. To obtain information for all AMPs on your system, use the SUM aggregate. For more information, see DiskSpace[V][X] in data dictionary.

Permanent Space Allocation

Permanent space is dynamically acquired by data blocks and cylinders when the system inserts rows. The data block is a disk-resident structure that contains one or more rows from the same table and is the physical I/O unit for the file system.Data Blocks are stored in physical disk sectors or segments, which are grouped in cylinders.

The total space of your entire Teradata Database configuration is derived by summing all database and user PERM limits. Total unallocated space is equal to the sum of all permanent limits minus the sum of all permanent space currently in use.

You can use the DBC.DiskSpace view to termine how much permanent spacei s being allocated to which database or user. The following table lists the fields that track perm space values.

CURRENTPERM :- The total number of bytes (including table headers) currently allocated to existing data tables, index tables, and subtables, stored procedures, triggers and permanent journals residing in a particular database/user.

This value is maintained on each AMP

MAXPERM : The maximum number of bytes available for storage of all (current and future) data tables, index tables, and subtables, stored procedure, triggers, and permanent journals owned by a particular database/user.

Note: For each database or user reported, the number of permanent bytes is divided by the number of AMPs in the configuration. The result is recorded on each AMP and may not be exceeded on that AMP. That is, a user may own several objects, as long as the combined storage requirements are within the MaxPerm limit set for that user on each AMP.

PEAKPERM: The largest number of bytes ever used to store data in a user or database since the last reset of this value to zero.

This value is maintained on each AMP.

To reset PeakPerm value to Zero, use the DBC.ClearPeakDisk macro.

Specifying Spool Space Limits:

Spool space is permanent space not assigned to any database or user and remains spool until permanent space is required.

The system needs spool space for TJs or to create spool files for processing queries when returning an answer. Spool space is especially important for queries that involves full table scans or user NUSIs.

The system uses spool space for the following :

. The response rows of every query run by that user during a session. Thus, each user needs a high enough spool allocation to contain the biggest anticipated answer set.

. Very large tables. Large tables usually require more available spool space than smaller tables, because intermediate rows are held in spool space during query execution.

. Large Volatile tables. These tables require more available spool space.

Spool Space Allocation

Teradata database allocates spool space dynamically only from disk cylinders that are not being used for permanent or temporary data.

Note: Permanent, temporary and spool data blocks can not coexist on the same cylinder.

Spool space is not reserved. All unused perm space in the Tearadata Database is considered available spool space. When spool is released, the file system returns the cylinders it was using to the free cylinder list.

Limiting spool space for a user helps reduce the impact of possibly bad queries. You set spool space limits for a database, a user, or a profile to limit spool space for a user, but you can not limit spool space at table level.

Defining Temporary Space Limits

Temporary space is used to hold rows of materialized global temporary tables. It is allocated at the database or user level, but not the table level.

You define a temporary space limit with the TEMPORARY parameter of a CREATE/MODIFY PROFILE or CREATE / MODIFY UISER/DATABASE statement.

note: A profile definition overrides any user definition. it does not append settings to the definition.

Query the DBC.DiskSpaceX view to find the system levels for temporary space. When using the CREATE USER, CREATE DATABASE or CREATE PROFILE statement to assign temporary space limits, keep your space limits in mind. Query the DBC.DiskSpaceX view to find the system levels for temporary space.

The following table describes the different types of temporary space.

CURRENTTEMP : This is amount of space currently in use by Global Temporary Tables.

PEAKTEMP : This is the maximum temporary space used since the last session.
Temporary space is released when the session terminates.

MAXTEMP : MaxTemp specifies the limit of space available for global temporary tables.

The may not exceed the limit of
1. The creator or modifier of the profile, when setting TEMPORARY in a profile.
2. The immediate owner of the user being created or modified, if a profile does not apply.

If you do not specify a value and the user is associated with a profile, MaxTemp defaults to the value of the profile, if defined. If the profile TEMPORARY is set to NULL or NONE, or the user is not associated with a profile, MaxTemp defaults to the value of teh parent of the user.


Increasing Space By Giving OwnerShip

This section describes how to increase the permanent space limits of a database or user by transferring a database or user to another database or user.

Transferring OwnerShip

You can transfer both database or users, but to simplify the discussion, this section describes databases. Note that you can easily replace any instance of the word "Database" in the following section with the word "user". Also note that databases can own users and users can own databases.

The GIVE statement transfers ownership of a database, including all the databases owned by that database. In addition, you transfer the permanent space limits defined for that database.

When you give a database to another database in the hierarchy, only the permanent space limit for that database is transferred. The spool and temporary space limits remain the same. All descendents of the given database remain descendents of that given database.

When you drop a database, its permanent space limit is created to its immediate owner. however, its spool space and temporary space is not credited to its immediate owner (that is, the immediate spool and temporary space allocation of the owner remains unchanged)

GIVE does not transfer and change explicit privileges.

Transferring Permanent Space

With Create, Give and Drop, you can transfer the permanent space of one database or user to another. This is particularly useful if you wish to transfer permanent space from a child of a child back to user DBC when user DBC is not the immediate owner.

For example, assume the following hierarchy:


Also assume that:
. F has a MAXPERM of 10, a MAXSPOOL of 50, and a MAXTEMP of 25
. E has a MAXPERM of 10, a MAXSPOOL of 20 and a MAXTEMP of 15

To increase permanent space for E:

1. From space owned by F, create temporary database X with MaxPerm of 5:
Create Database X from F as PERM = 5;
The default is to allocate to a new database the same spool and temp space as its owing database, so MAXSPOOL for X defaults to 50 and MAXTEMP for X defaults to 2. The PERM allocation for X is taken from the space of its owning database; thus, the MAXPERM of F is reduced to 5.

2. Give X to E by using the GIVE statement to transfer ownership.
GIVE X To E;

3. Drop X with the following statement :

Drop Database X;

This increases the MAXPERM of E to 15.

The MAXSPOOL and MAXTEMP of E are unchanged at 20 and 15, respectively.