15.00 - Calculating Total PERM Space Requirements - Teradata Database

Teradata Database Design

Teradata Database
User Guide

Calculating Total PERM Space Requirements

Use the following procedure to determine how much PERM space to allocate to user SysAdmin.

1 Estimate the size of each database, as follows.

a Estimate the size of the primary data table, including fallback (see “Sizing Base Tables, LOB Subtables, XML Subtables, and Index Subtables” on page 858 for instructions for how to do this) and LOB and XML subtables.

LOB and XML values are also stored in the permanent journal, so LOB and XML column space must account for additional permanent journal append and storage costs in addition to LOB and XML subtable storage costs.

b Estimate the size of unique and nonunique secondary index subtables, join indexes, and hash indexes.

c Add the primary data table estimate and index and LOB and XML subtable estimates (including fallback) to obtain the estimated total table size.

2 Estimate the total table storage by adding together the space estimates of all table sizes (Substeps a, b, and c). Use this sum for step 3.

3 Estimate the space requirement for the application.

Note: If the calculated sum is greater than the remainder calculated in step 4, contact your Teradata sales representative to discuss a system expansion.

a Add 7% for fragmentation.

b Add extra space for spooling, TEMP space, and for variability in hashing. Although this space requirement varies according to the applications, adding 20% to 30% is usually adequate if you do not use permanent journaling.

c Estimate the size of each journal table per database.

d Note that if journaling is used, the extra space requirement depends on two factors:

  • Size of the data tables that write to that journal
  • Number of changes applied to those tables before the journal table is dropped
  • e Add the sums calculated for steps 1 through 4 and use their sum for the calculation in step 5.

    f For each disk, add 3 cylinders per disk as spaces and allow 2% of the formatted space for cylinder indexes.

    4 Subtract the amount of space needed to accommodate user DBC contents plus your maximum WAL log from the user DBC PERM space.

    Specify about 80 MB for the growth of system tables and the WAL log plus another 5% of the current PERM space for spool growth.

    Use the remainder for step 5.

    5 If possible, subtract the sum of step 3 from the result of step 4.

    6 Deduct the number of cylinders that make up the default free space specified by the DBS Control record for operations that use the percent freespace (FSP) value.

    For example, if your FSP is set to 15, deduct an additional 15%.

    If you plan to create large tables with a freespace percentage greater than the GDO default, then use the larger percentage.

    For example, if you define your largest tables with an FSP of 30, then deduct an additional 30%.

    The remainder is the amount of PERM space you should allocate to the SysAdmin user.

    Note: Table sizing is normally the responsibility of Teradata field support personnel.