IBM 000-8697 User Manual
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IBM Informix OnLine Database Server Administrator’s Guide
Structure of a Dbspace Bit-Map Page
Two bits are all that are needed to describe page fullness for these limited
conditions, as illustrated here.
conditions, as illustrated here.
4-Bit Bit-Mapped Pages
The 4-bit bit-map pages track available space in extents allocated to tables
that contain rows longer than a page, or rows that include VARCHAR, BYTE,
or TEXT data types. Four bits are needed to describe all possible combina-
tions of page fullness for these extents, as illustrated below. The terms used
to describe page fullness describe row segments as whole-page, partial-page,
and small. These segment sizes are relative to available free space and are
selected on the basis of performance.
that contain rows longer than a page, or rows that include VARCHAR, BYTE,
or TEXT data types. Four bits are needed to describe all possible combina-
tions of page fullness for these extents, as illustrated below. The terms used
to describe page fullness describe row segments as whole-page, partial-page,
and small. These segment sizes are relative to available free space and are
selected on the basis of performance.
Bit Values
Description of Page Fullness
00
Page is unused
10
Page is used completely (index page)
01
Page is partially used (data page)
11
Page is full (data page)
Bit Values
Description of Page Fullness
0000
Page is unused
0100
Home data page has room for another data row
1000
Page is used completely (index page)
1100
Home data page is full
0001
Remainder page, can accept whole-page segments
0101
Remainder page, room for partial-page segments
1001
Remainder page, room for small segments
1101
Remainder page, no room for even small segments
0010
Blob page, can accept whole-page segments
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