IBM 000-8697 Manual Do Utilizador
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.
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.
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.
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
managed by OnLine
contains three
structures: a page
header, a page-
ending timestamp,
and a a slot table.
Timestamp
(4 bytes)
(4 bytes)
Page header
(24 bytes)
Page structure
Slot table
(4 bytes per entry)
Free space in the page