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(d) Give the log records written in the fuzzy (indirect) checkpoint taken at the end
of the recovery.
4.2
Repeat items (b) and (d) in the previous problem in the case that pages f , p,
and q were flushed onto disk during normal processing between the writing of the
log records with
LSN
s 112 and 113 and that page q is flushed onto disk during the
redo pass between the scanning of the log records with
LSN
s 114 and 115.
4.3
As stated in Theorem
4.4
about the analysis pass of
ARIES
recovery, the active-
transaction table reconstructed in the analysis pass exactly represents the states of
active transactions at the time when the last log record survived on the log disk was
written, while the reconstructed modified-page table may not represent exactly the
set of modified pages with their
M
ODIFIED
-LSN
s at the same timepoint. Show that the
reconstructed modified-page table may contain pages whose
R
EC
-LSN
s are less than
their
M
ODIFIED
-LSN
s, and even pages that are unmodified, at the time of the system
crash. Do such pages cause any harm?
4.4
In the redo pass of the
ARIES
algorithm, an update is redone on page p only if
the
P
AGE
-LSN
of p is less than the
LSN
of the log record for the update. In the undo
pass, the
P
AGE
-LSN
of page p is not inspected in order to verify that the update to be
undone really is on p,thatis,the
P
AGE
-LSN
of p is greater than or equal to the
LSN
of the log record for the update. Why is that verification unnecessary?
4.5
What actions should be taken for a new failure that occurs during restart
recovery when the
ARIES
algorithm is in the middle of its (a) analysis pass, (b)
redo pass, (c) undo pass?
4.6
During normal transaction processing, a great deal of log records are created.
At which location (
LSN
) is it possible to truncate the head of the log file and dispose
of the oldest log records?
4.7
In the undo pass of recovery, the log is flushed every time the rollback of some
transaction is completed (Algorithm
4.16
). The log is also flushed during normal
transaction when a transaction completes its rollback (Sect.
3.8
, Algorithm
3.3
). The
flushing of the log is not absolutely necessary in these cases. Explain why. However,
it is advantageous to do so. Why?
4.8
Case (2) of Example
4.1
suggests that with the do-undo-redo recovery
paradigm, we should not log undo actions, in order to avoid advancing the
P
AGE
-
LSN
of a page above the
LSN
s of log records for actions to be redone later on that
page. Can you make this approach viable? What problems do you observe? With
the do-redo-undo recovery paradigm of
ARIES
, it is absolutely necessary to log the
undo actions. Which of the functions of
ARIES
would not work if the undo actions
were not logged?
4.9
Consider the extended read-write transaction model in which a transaction can
use the action CŒx to declare the updates on x done so far as committed before the
transaction terminates (see Problems
1.5
and
3.5
). An update declared as committed
becomes immediately visible to other transactions and will not be undone even if the
