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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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Teradata RDBMS Database Administration

3 - 1 Chapter 3: Space Considerations

Defining Permanent Space Limits

Defining Permanent Space Limits

You set permanent space limits at the database or user (not table) level. You define the maximum limit with the PERM parameter of a CREATE/MODIFY USER/DATABASE statement. This allocation is deducted from the limit of the immediate parent of the object being created.

Note: The amount of permanent space specified for each user or database 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, you may create several objects in your own space, as long as the combined storage requirements do not exceed the MaxPerm limit set for you on each AMP.

When you drop an object, its permanent space is released to the immediate parent.

Permanent Space Allocation

Permanent space is used to store tables, indexes, stored procedures, triggers, and permanent journals.

Permanent space is dynamically acquired by data block and cylinder when rows are inserted. 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 Teradata file system. Data blocks are stored in physical disk sectors or segments, which are grouped in cylinders.

Note: You can define the maximum data block size at the global or table level (see "Permanent Space Availability" on page 3-3), but this does not affect the permanent space available for storage of those blocks.

Permanent space is reported by database or user, so total space for your entire Teradata RDBMS 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. (For instructions and examples, see "Monitoring Disk Space Activity" on page 3-12.)

Permanent space is tracked by the following:

Type Description
CURRENTPERM 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.

3 - 2

Teradata RDBMS Database Administration Chapter 3: Space Considerations

Defining Permanent Space Limits

MAXPERM Maximum number of bytes available for storage of all (current and future) data tables, index tables and subtables, stored procedures, 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 PeakPerm is the largest number of bytes being used to store data in a user or database. This value is maintained on each AMP. To reset the PeakPerm value to zero, use the DBC.ClearPeakDisk macro. For more information on this macro and how to use it, see "Resetting Peak Values in DBC.DataBaseSpace" on page 3-13 and Teradata RDBMS Data Dictionary.

For more information about permanent space allocation (including the ramifications of space allocation for users DBC, SystemFE, and SysAdmin), see "Permanent Space Allocations" in Teradata RDBMS Database Design.

Permanent Space Availability

When you create a new database or user, permanent space limits are deducted from the available (unused) space of the immediate owner of that database or user. Initially, all available permanent space is allocated to user DBC (see "The Initial Teradata Database" on page 1-3). A hierarchy is formed as you create other users and databases.

Unused space is allocated dynamically for temporary or spool space, which can reduce the actual amount of permanent space available at a given point in time. Thus, specifying a PERM limit does not guarantee that a session will be able to appropriate all of that space upon demand.

Note: A transaction is aborted when it requires more space than is currently available for the requesting user. To protect transactions, you can specify that a number of cylinders be reserved for transactions needing permanent space.

Reserving Cylinders for Permanent Space Allocation

Requests for a new PERM or SPOOL cylinder are both satisfied from the pool of free cylinders.

The number of free cylinders to keep in reserve for requests needing permanent space is determined by the File System field named Cylinders Saved for PERM in the DBSCONTROLGDO. When a statement requires space, this field determines allocation as follows:

3 - 2 Teradata RDBMS Database Administration

Chapter 3: Space Considerations

Defining Permanent Space Limits

IF the statement needs ... AND there are . THEN the statement .
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