Release 10.1A: OpenEdge Getting Started:
Database Essentials

Calculating database storage requirements

The OpenEdge database engine stores all database fields and indexes in variable-length format and does not store trailing blanks in character fields or leading zeros in numeric fields. The benefits of this variable-length storage technique are:

Disk storage is reduced.
An application is easier to change since you can increase the maximum storage space for a field without copying or restructuring the entire database. You can put more characters into newly created records without affecting existing records.

Table 4–1 lists the formulas you use to calculate the field storage values (in bytes) for different data types.

Table 4–1: Formulas for calculating field storage

4GL Data type (SQL equivalent)	Value	Field storage in bytes
CHARACTER (VARCHAR)	Character string	1 + number of characters, excluding trailing blanks. If the number of characters is greater than 240, add 3 to the number of characters instead of 1.
DATE (DATE)	Date	3
DECIMAL (DECIMAL or NUMERIC)	Zero	1
	Nonzero	2 + (number of significant digits + 1) / 2
INTEGER (INTEGER)	Zero to 126	1
	127 to 32,766	2
	32,767 to 7.99 million	3
	8 million to 1.99 billion	4
	2 billion	5
LOGICAL (BIT)	False	1
	True	2

For example, you calculate the estimated database size for a database with a single customer table as follows.

The table has three fields:

Cust-num — An integer field that is always three digits.
Name — A character field containing 12–30 characters, with an average of 21 characters.
Start-date — A date field.

The table is indexed on just one field (Name) and you would expect to have about 500,000 records in the customer table. Table 4–2 lists formulas (and examples) for estimating the size of your database.

Table 4–2: Calculating database size 

Database component	Size
Schema	=  421,000 (This number is the size of an empty database with  the schema loaded in.)
Field storage	= Cust-num + Name + Start-date = 3 + 21 + 3  = 27
Customer table	= number of records x field storage x 1.5 = 500,000 x 27 x  1.5  = 20,250,000
Name index	= number of records x (7 + number of fields in index +     index field storage ) x  2  = 500,000 x (7 + 1 + 21) x 2  = 29,000,000
Database	= schema size + data table size + index size = 421,000 + 20,250,000 + 29,000,000  = 49,671,000 bytes

These formulas are conservative since they often result in a large estimate of your database size. However, you also must allow for temporary disk space for each database user for the following purposes:

Sorting. (Allow twice the space required to store the table.)
Temporary storage of the primary recovery (BI) area.
Before-image storage in the primary recovery area.
After-image storage in the after-image storage area.

Database-related size criteria

When planning the size of your database, use the formulas listed in Table 4–3 to calculate the approximate amount of disk space (in bytes) required for a database. See OpenEdge Data Management: Database Administration for limits on any of these elements.

Table 4–3: Formulas for calculating database size 

Size	Formula
Database size	schema size + data table size + index size.
Schema size	Typically, between 1 and 100MB1.
Data table size	Sum of individual table sizes.
Individual table size	number of records x field storage x 1.5.
Index size	Sum of individual index sizes.
Individual index size	number of records in the table being indexed   x (7 + number of fields index +field storage)  x 2.

1To determine the schema size, load the schema into an empty database and check the size of your database—this is the size of your schema.