Chapter 10 Generating a Database from a PDM

Estimating Database Size

You can estimate the size of a database for all the tables in the model or for only selected tables throughout the model.

Basis of calculation

You obtain an estimate based on the following elements:

Estimated number of records in tables
Columns in each table
Indexes in the model
Tablespaces in the model
Database storage options

Estimation depends on parameters like DBMS type, physical options, column data types, indexes and keys. The estimation formula used in this feature proceeds from the DBMS documentation.

Records in tables
You indicate a number of records in each table in your model.

Columns

The estimated database size for a column is based on the following:

Size of fixed length data types
Average size of variable length data types

Indexes

The estimate of the database size includes all indexes including primary key indexes, foreign key indexes, alternate key indexes and database-specific indexes such as IQ join indexes.

Automatic index constraints
The automatic indexing of keys is DBMS specific. If the target database supports the automatic indexing of keys, the resulting database size estimation includes these indexes.

Tablespace size

The size of a tablespace associated with a table is estimated by default, and is displayed as a total of the following:

All tables in the tablespace
All indexes in the tablespace

For more information on how to associate a tablespace with an index or table, see section Creating an Index in chapter Building Physical Diagrams.

Storage options

Data storage options are DBMS specific. You define data storage options supported by the target database. These are included in the estimate of database size.