- Rollback
an update
when using an undo log:
- In undo logging,
dirty data
(written by uncommitted transactions)
are found
in
memory buffers
and
on disk:
Where to find dirty data and the old (orignal value) of a database element (A):
- Rollback procedure for
the undo log:
- Use the
old/original value in the
undo log
to:
- Restore the value of the database element on disk and in the memory buffer
Graphically:
- Use the
old/original value in the
undo log
to:
- In undo logging,
dirty data
(written by uncommitted transactions)
are found
in
memory buffers
and
on disk: