IBM 000-8697 User Manual
System Architecture
2-129
Data Pages and Data Row Storage
Storage of Modified Rows
When a row is modified, OnLine attempts to return the modified row to its
current location. If the row size is unchanged, no changes are needed in the
slot table. If the row is smaller than before, OnLine changes the slot table
entry for this row to reflect the new row length. If the row no longer fits,
OnLine attempts to store the row in another location on the same page. If
OnLine can do this, the slot table entry is changed to reflect both the new
starting offset and the new length of the row.
current location. If the row size is unchanged, no changes are needed in the
slot table. If the row is smaller than before, OnLine changes the slot table
entry for this row to reflect the new row length. If the row no longer fits,
OnLine attempts to store the row in another location on the same page. If
OnLine can do this, the slot table entry is changed to reflect both the new
starting offset and the new length of the row.
If the modified data row is shorter than a page but cannot be accommodated
on the current page, a 4-byte forwarding pointer (containing the new rowid)
is stored on the home page. The data row retains its original rowid, which is
stored in the index page. The data is moved to the new page and the space
freed by the move is available for other rows.
on the current page, a 4-byte forwarding pointer (containing the new rowid)
is stored on the home page. The data row retains its original rowid, which is
stored in the index page. The data is moved to the new page and the space
freed by the move is available for other rows.
storage if the updated row is too large for the home page but shorter than a
whole page.
whole page.