DBMS Query Optimization essay

1
1: Question optimization (2 factors)
Think about the next relations:
R(A, B, C, D, E)
S(F, D)
T(G, B, D, H)
U(I, J, Okay)
V(L, J, M)
W(L, J, N)
Counsel an optimized logical question plan for the above question and clarify why your proposed plan
could also be quicker than different attainable plans. It’s best to discover one of the best guess(es) for the be a part of order in
your plan with out understanding the statistics of the be a part of attributes and base relations.
SELECT B,C
FROM R, S, T, U, V, W
WHERE R.D = S.D and R.D = T.D
and R.B = T.B and U.J <= V.J and U.J = W.J and R.E <= 200 and W.N <= 100
Please notice that your reply could not at all times be extra environment friendly than different plans, but it surely ought to run
quicker than different plans for many enter relations.
2: Question optimization (four factors)
For the 4 relations within the following desk, discover one of the best be a part of order in keeping with the dynamic
programming algorithm utilized in System-R. It’s best to give the dynamic programming desk
entries for evaluating the be a part of orders. The price of every be a part of is the variety of I/O accesses the
database system performs to execute the be a part of. Assume that the database system makes use of the
two-pass sort-merge be a part of algorithm to carry out the be a part of operations. Every block comprises four tuples
and tuples of all relations have the identical dimension. We have an interest solely in left-deep be a part of timber. Observe
that it’s best to use the System-R optimizer method to compute the scale of every be a part of output.
R(A,B,C) S(B,C) W(B,D) U(A,D)
T(R)=4000 T(S)=3000 T(W)=2000 T(U)=1000
V(R,A) =100
V(R,B) =200
V(R,C) =100
V(S,B) =100
V(S,C) = 300
V(W,B) =100
V(W,D) =50
V(U,A) =100
V(U,D) =100
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three: Question optimization (2 factors)
What’s the time-complexity of the dynamic programming algorithm you utilized in query (three) of
this project? It’s best to clarify your reply.
four: Serializability and 2PL (5 factors)
(a) Think about the next lessons of schedules: serializable and 2PL. For every of the next
schedules, state which of the previous lessons it belongs to. If you happen to can’t resolve whether or not a
schedule belongs in a sure class based mostly on the listed actions, clarify briefly. Additionally, for every 2PL
schedule, establish whether or not a cascading rollback (abort) could occur. A cascading rollback will
occur in a schedule if a given transaction aborts sooner or later within the schedule, and no less than one
different transaction have to be aborted by the system to maintain the database constant. (four factors)
The actions are listed within the order they’re scheduled and prefixed with the transaction identify. If
a commit or abort shouldn’t be proven, the schedule is incomplete; assume that abort or commit should
comply with all of the listed actions.
1. T1:R(X), T2:R(Y), T3:W(X), T2:R(X), T1:R(Y)
2. T1:R(X), T1:R(Y), T1:W(X), T2:R(Y), T3:W(Y), T1:W(X), T2:R(Y)
three. T1:W(X), T2:R(X), T1:W(X)
four. T1:R(X), T2:W(X), T1:W(X), T3:R(X)
(b) Think about a database DB with relations R1 and R2. The relation R1 comprises tuples t1 and t2
and the relation R2 comprises tuples t3, t4, and t5. Assume that the database DB, relations, and
tuples type a hierarchy of lockable database components. Clarify the sequence of lock requests and
the response of the locking scheduler to the next schedule. You could assume all lock requests
happen simply earlier than they’re wanted, and all unlocks happen on the finish of the transaction, i.e., EOT.
(1 level)
• T1:R(t1), T2:W(t2), T2:R(t3), T1:W(t4)
5: Levels of Consistency (four factors)
(a) Think about the schedule proven in Desk 1.
What are the utmost levels of consistency for T1 and T2 on this schedule? You could discover the
most levels of consistency for T1 and T2 that makes this schedule attainable. (2 factors)
(b) Think about a transaction that reads the details about a set of accounts from a CSV file
and writes them in a database. What diploma of consistency will you select for this transaction?
three
T1 T2
zero begin
1 learn X
2 write X
three begin
four learn X
5 write X
6 Commit
7 learn Y
eight write Y
9 Commit
Desk 1: Transaction schedule
It’s best to justify your reply. Subsequent, think about one other transaction in a banking system that
reads the balances of all financial institution accounts in a department and computes their common. What diploma of
consistency will you select for this transaction? It’s best to justify your reply. (2 factors)
6: Serializability (6 factors)
Think about the next protocol for concurrency management. The database system assigns every
transaction a novel and strictly more and more id at the beginning of the transaction. For every information
merchandise, the database system additionally retains the id of the final transaction that has modified the info
merchandise, referred to as the transaction-id of the info merchandise. Earlier than a transaction T needs to learn or write on
a knowledge merchandise A, the database system checks whether or not the transaction-id of A is larger than the id
of T . If so, the database system permits T to learn/write A. In any other case, the database
system aborts and restarts T.
(a) Does this protocol enable solely serializable schedules for transactions? If not, you could recommend
a change to the protocol so that each one schedules permitted by this protocol are serializable. You
ought to justify your reply. (three factors)
(b) Suggest a change to this protocol or the modified model you’ve got designed for half (a) that
will increase its diploma of concurrency, i.e., it permits extra serializable schedules. (three factors)

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