Database Reference
In-Depth Information
• Step 3: If a transaction
T
j
exists in the execution phase, the
scheduler has three cases:
• Case 1:
L
(
T
i
) >
L
(
T
j
). Step 4 is done, where
L
(
T
i
),
L
(
T
j
) are
the classification levels of the transactions
T
i
,
T
j
.
• Case 2:
L
(
T
i
) =
L
(
T
j
). Step 5 is ruined.
• Case 3:
L
(
T
i
) <
L
(
T
j
).
− The scheduler denies
T
j
.
− Set
T
i
is in the invisible area of
T
j
.
− Create a new version of the data and an infinite write
timestamp is defined to it.
− The transaction
T
i
will be executed immediately to
overcome the covert channel problem.
− If (
R
-set
done
T
j
∩
W
-set
remaining
T
i
≠ φ)|(
R
-set
done
T
j
∩
R
-set
remaining
T
i
≠ φ), then
T
i
is added into
C
-set
T
j
.
− Perform step 6.
• Step 4: If the low transaction
T
j
is in the execution phase, the
scheduler will make the high classification level transaction
T
i
wait until
T
j
commits and will perform step 6.
• Step 5: If the two transactions have the same classification
level, the scheduler will execute them at the same time.
• If (
W
-set
remaining
T
j
∩
R
-set
done
T
i
≠ ϕ) & (
W
-set
remaining
T
j
∩
W
-set
remaining
T
i
≠ ϕ), then
T
i
will enter an invisible area
of
T
j
for the time of the creation of a new version of con-
flicted data. After each of
T
i
and
T
j
are committed, step 6
will be performed.
• Step 6: If the transaction
T
is the only transaction that is run
at step 2, the scheduler will wait for other transactions to be
submitted. Otherwise, the scheduler will execute the transac-
tion, say
T
K
,
that has the lowest classification level among the
waiting transactions. The infinite write timestamp is assigned
to the new versions in the invisible areas of
T
K
. Figure 7.2
shows the flow chart for the enhanced secure multiversion
concurrency control model.
7.4 Performance Evaluation
The performance of the enhanced secure multiversion concurrency
control model will be evaluated using two classification levels (high
and low) in the simulation.
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