2-130 IBM Informix OnLine Database Server Administrator’s Guide
Data Pages and Data Row Storage
Ifthe modified data row is longer than a page, OnLine first begins to divide
the data into whole-page segments, starting from thetail end of the row.
OnLine then attempts to fit the leading segment plus four bytes (for the
forwardpointer) into the current location of the row on the home page. If the
leading segment fits, the whole-page tail segments are stored in big-
remainder pages and forwarding pointers are added.
Figure2-30
Updated rows that
nolonger fit in their
original pages but
are shorter than a
full page receive a
forwardpointer and
are stored on a
different page.
Modified row
New, longer row after processing
Header
Original row size and location
Header
Forward pointer (rowid) to new location
1. Data storage before data is modified
3. Data storage after data is modified
Newly freed space
Header
2. Data is modified
Modified slot table
entry for data row