Database Reference
In-Depth Information
7.3 Enhanced Secure Multiversion Concurrency Control Model
The enhanced secure multiversion concurrency control model is based
on the Rajwinder Singh proposed model to prevent creating the covert
channel without retrieval anomaly and to be free of the starvation of
the high-level transaction for multilevel relational database transac-
tions. The enhanced model improves on the Rajwinder Singh model
by splitting the write set of the low-level transactions that conflict
with the read set of the high-level transactions into “done” and
“remaining.” This modification reduces the size of
C
-set
T
H
by relaxing
the condition used in the Rajwinder Singh model without affecting
the security of the database.
The enhanced secure multiversion concurrency control model
divided
W
-set
T
L
into two parts:
W
-set
done
T
L
and
W
-set
remaining
T
L
.
W
-set
done
T
L
∪
W
-set
remaining
T
L
=
W
-set
T
L
.
W
-set
done
T
L
contains data written by
T
L
and
W
-set
remaining
T
L
contains
data to be written by
T
L
.
The enhanced secure multiversion concurrency control model
also used an infinite timestamp instead of using t-lock to solve the
problem of the retrieval anomaly. When a transaction
T
is inserted
into the concurrency control manager, it will be assigned to a unique
timestamp, defined asts(T).
T
). If a transaction
T
creates the
i
ith versions
of the data item
A
, an infinite write timestamp defined as
W
ts
(
A
i
) will
be assigned. Then it will be updated with ts(T)
T
) when
T
commits.
So, the read operation during its execution will get the version of
data item
A
in which its write timestamp is the recent timestamp and
is lower than or equal to its timestamp.
The enhanced secure multiversion concurrency control model
assumes that there is one scheduler that manages all the multilevel
transactions.
The enhanced secure multiversion concurrency control model con-
tains the following six steps:
• Step 1: When transaction
T
i
is entered to the scheduler,
R
-set
T
i
and
W
-set
T
i
will be received.
• Step 2: If no transaction exists in the execution phase, the
scheduler runs and the scheduler will perform step 6.
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