Figure 4-1 shows the physical structure of a database.

Figure 4-1 Database physical structure

Explanation

• HiRDB file system area
  This is an area in which HiRDB files are created.
  
• HiRDB file
  This is a type of file unique to HiRDB that is used to store table and index data.
  
• Segment
  This is the smallest unit of table and index data storage. One segment stores data from only one table or one index. A segment is composed of multiple, consecutive pages.
  
• Page
  This is the smallest unit of database I/O operations. If the page size is large, one page can store several consecutive rows, thus reducing the number of I/O operations in situations where the data is processed in the same order in which it is stored. Table 4-1 lists the available types of pages.
  

  Table 4-1 Types of pages

  Page type	Explanation
  Data page	Stores row data for a table.
  Index page	Stores index key values.
  Directory page	Stores management information on the status of RDAREAs.

Specifying the physical structure of a database

The physical structure of a database is specified when its RDAREAs are defined. Specifically, the physical structure is specified in the following control statements:

• create rdarea statement of the database initialization utility (pdinit)
• create rdarea statement of the database structure modification utility (pdmod)

Following is an example of specifying the create rdarea statement:

create rdarea USRRD01 for user used by PUBLIC 1 page 4096 characters 2 storage control segment 20 pages 3 file name "C:\rdarea01\file01" 4 initial 150 segments ; 5

Explanation

1. Specifies a name (USRRD01) for an RDAREA.
2. Specifies 4096 bytes as the page size.
3. Specifies 20 pages as the segment size.
4. Specifies the name of the HiRDB file system area where the RDAREA will be stored and a HiRDB file name:
   C:\rdarea01: Name of HiRDB file system area
   file01: HiRDB file name
   
5. Specifies the number of segments.