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2-120 IBM Informix OnLine Database Server Administrator’s Guide
Structure of a Dbspace Page
Structure of a Dbspace Page
The basic unit of OnLine I/O is a page. Page size might vary among
machines. The page size for your machine is specified as BUFFSIZE in the
configuration file. You cannot modify the page size.
Pages in a dbspace are allocated in a group called an extent. Pages can be
categorized according to the type of information they contain. All pages
managed by OnLine adhere to a similar structure, although the function of
the page can alter slightly the size of structures within the page. Figure 2-25
illustrates the three structures that appear on every OnLine page:
■ Page header (24 bytes including one 4-byte timestamp)
■ Page-ending timestamp (4 bytes)
■ Slot table (4 bytes per entry)
Figure 2-25
Every dbspace page
managed by OnLine
contains three
structures: a page
header, a page-
ending timestamp,
and a a slot table.
Timestamp
(4 bytes)
Page header
(24 bytes)
Page structure
Slot table
(4 bytes per entry)
Free space in the page