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7 Structure of pages When creating a database using DDL and SSL, the user does not usually require infor-
mation on the structure of pages, records and tables.
The following two chapters are intended as a reference section for users intere sted in
special details.
The entire storage space provided for the data in a database is divided int o realms. Every
realm consists of a specific number of pages that is specified when creating the databa se.
This number may be subsequently modified (see the "Creation and Restr ucturing" manual).
The length of a page may be 2048, 4000 or 8096 bytes and must be uniform within a
database. This page length is defined when creating the database with the BCREATE utility
routine and can be subsequently extended with BPGSIZE (see the "Creation and Restruc-
turing" manual for details).
Pages with a length of 4000 or 8096 bytes are each embedded in a page container, which
consists of a 64-byte header that precedes the page itsel f, and a 32-byte trailer at the end.
The following types of pages can be distinguished in the structur e of a realm. These pages
differ in their data contents and structure:
Act-key-0 page
contains realm-specific data; is always the first page in a real m
Act-Key-N page
contains realm-specific data; is always the last page in a realm
FPA page
serves free place administration (FPA) on realm level. At least one FPA page is
always present.
DBTT anchor page
manages the DBTT areas of a record type (DBTT: Database Key Translation Table).
DBTT page
page of a DBTT area. Manages the records of a record type.
CALC page
contains a hash area
Data page
contains records which are not stored in a hash area, and tables (except DBTT)