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Recent questions tagged database

0 votes
0 answers 4 views
Q7, from this assignment: https://nptel.ac.in/content/storage2/courses/106104135/assignment6.pdf S1 : r1(x),r2(x),w2(x),r3(x),w1(x), w2(y),r3(y),w3(x) S2 : r2(x),r1(x),w1(x),w2(x),w2(y),r3(x),w3(x),r3(y) Check whether they are view equivalent or not. ... read the initial value. In this case, initial value of x is read by T1 in S1, while in S2, it is read by T2. So are they view equivalent or not?
asked 16 hours ago in Databases goxul 109 points 4 views
0 votes
2 answers 3 views
Consider the following schedule S T1 T2 T3 T4 Timestamp R(X) R(Y) t1 W(X) W(Y) t2 R(Y) R(X) t2 W(Y) W(X) t4 R(X) t5 W(X) t6 R(X) denotes read operation on data item X by Transcation Ti. W(X) denotes write operation on data item X by Transcation Ti. Choose the correct execution order for the above schedule S. a)T3-T2-T1-T4 b)T2-T3-T1-T4 c)T2-T4-T3-T1 d)T4-T2-T3-T1
asked 4 days ago in Databases sekhar_1621 13 points 3 views
0 votes
1 answer 7 views
Consider the following schedule T1 T2 T3 R(X) R(Y) R(Z) W(Z) W(Y) R(X) R(X) denotes read operation on data item X by Transcation Ti. W(X) denotes write operation on data item X by Transcation Ti. How many conflict serializable schedule are possible for the above schedule? a)6 b)5 c)3 d)8
asked 4 days ago in Databases sekhar_1621 13 points 7 views
0 votes
1 answer 5 views
In the context of timestamp-ordering protocol which of the following must be correct ? a)if TS(Ti)>=R-timestamp(Q),the operation is rejected b)if TS(Ti)>W-timestamp(Q),the operation is rejected and Ti is rolled back c)if TS(Ti)< W-timestamp(Q),the operation is rejected and Ti is rolled back d)if TS(Ti)< W-timestamp(Q),W-timestamp(Q) is set to TS(Ti).
asked 4 days ago in Databases sekhar_1621 13 points 5 views
0 votes
2 answers 11 views
Which of the following statements are false ? a)if any schedule is neither conflict serializable nor view serializable then that schedule must be inconsistent b)Timestamp protocol ensures freedom from deadlock c)Strict Two phase locking protocol ensures cascadeless rollback d)Lock point of a schedule in two phase locking protocol indicates final lock of the schedule
asked 4 days ago in Databases sekhar_1621 13 points 11 views
0 votes
1 answer 24 views
T1 T2 R(A) W(A) R(A) W(A) Dirty read problem is obviously here but if R2(A) comes between W1(A) and W2(A), but is it lost update problem?
asked Sep 14 in Databases Sambhrant Maurya 204 points 24 views
1 vote
1 answer 6 views
For two schedules, their precedence graphs are isomorphic. Can it be inferred that the schedules are conflict equivalent?
asked Sep 14 in Databases Sambhrant Maurya 204 points 6 views
0 votes
0 answers 12 views
suppose there is a relation R(A,B,C) and A is the candidate key. AB → C is a F.D. does this violate 2NF ( doubt is that whether AB should be considered as subset of C.K. or not for checking partial dependency) and now we have another R(A,B,C,D), suppose BC forms C.K D → AB (whether this FD violates 3NF or not)
asked Sep 13 in Databases ummokkate 45 points 12 views
0 votes
0 answers 4 views
If anyone having any idea how to solve mainly the (b) part. Please help me out. Consider a relation R with five attributes ABCDE.For each of the following instances of R, state whether it violates (a) the FD BC→ D and (b) the MVD BC →→ D: (a) { } (i.e., empty relation) (b) {(a,2,3,4,5), (2,a,3,5,5)} (c) {(a,2, ... , (a,2,3,6,5), (a,2,3,6,6)} (g) {(a,2,3,4,5), (a,2,3,6,5), (a,2,3,6,6), (a,2,3,4,6)}
asked Sep 13 in Databases कुशाग्र गुप्ता 46 points 4 views
0 votes
0 answers 4 views
Consider the following collection of relations and dependencies. Assume that each relation is obtained through decomposition from a relation with attributes ABCDEFGHI and that all the known dependencies over relation ABCDEFGHI are listed for each question. (The questions are independent of each other, obviously, since the given dependencies ... G, G → H 4. R4(D,C,H,G), A → I, I → A 5. R5(A,I,C,E)
asked Sep 11 in Databases कुशाग्र गुप्ता 46 points 4 views
0 votes
0 answers 12 views
What do you mean by Seek? For Natural Loop Join, we calculate No. of Seeks are (nr + br). Assume that, Relation r is called the Outer Relation and Relation s is called the Inner Relation. (ni,bj) – ni represents total no. of tuples and bj represents no. of blocks in that relation. Reference (Korth) – For Block Nested-Loop Join –
asked Sep 10 in Databases ayushsomani 13 points 12 views
1 vote
1 answer 13 views
I am having few doubts in Tuple Relational Calculus and finding it difficult. Please, can you help me in understanding this. Doubt-1: Is this Query unsafe coz of ¬employee(x)? I am really confused coz this links says that (https://www2.cs.sfu.ca/CourseCentral/354 ... - https://gateoverflow.in/1258/gate2007-60 Doubt-2: Why we haven't changed belongs to to not belongs to while applying the negation?
asked Sep 10 in Databases ayushsomani 13 points 13 views
0 votes
0 answers 10 views
Please check this table is correct or not – Recoverability Serializability Deadlock free Starvation free 2PL No Yes No No Strict 2PL Yes Yes No No Rigorous 2PL Yes Yes No No conservative 2PL Yes Yes Yes No Timestamp ordering protocol(TSP) No Yes yes No Strict TSP Yes Yes Yes No Thomas write rule No yes Yes No Strict TSP + wound-wait + wait-die Yes Yes Yes Yes
asked Sep 9 in Databases MRINMOY_HALDER 27 points 10 views
0 votes
0 answers 12 views
What is the best strategy to approach these kind of questions? I am facing difficulties in solving indexing numericals. Any help would be highly appreciated. Thank you.
asked Sep 8 in Databases DukeThunders 132 points 12 views
0 votes
0 answers 58 views
What happens when R1/R2 & R2 is NULL ????
asked Sep 8 in Databases MRINMOY_HALDER 27 points 58 views
0 votes
1 answer 57 views
https://gateoverflow.in/96566/view-serializable S1: R(A) W(A) W(B) S2: R(A) W(A) R(B) W(B) How many view serializable schedules are possible which are not conflict serializable? (A) 0 (B) 1 (C) 2 (D) 3 The above question has ... -dbms-view-conflict-serializable-schedules?show=77897#q77897 It is showing the question has been hidden. Can anyone explain to me the actual solution of the question ?
asked Aug 27 in Databases user2525 1.5k points 57 views
0 votes
1 answer 16 views
For the following schedule ( Link : https://gateoverflow.in/26378/view-serializability ) , check whether it is view serializable or not. T1 T2 W(A) W(A) R(A) There is a cycle in the precedence graph. So, it is not conflict serializable. There are 2 blind ... before T2 does. The graph becomes : Since there is a cycle in the polygraph, the schedule is not view serializable. Is my approach correct ?
asked Aug 26 in Databases user2525 1.5k points 16 views
0 votes
1 answer 26 views
1. There are 2 relations: gate2016 (exam_date, exam_center, branch_id) and candidate (rollno, name, bid, refno, choice_of_date). In a candidate relation, bid is the foreign key which refers to the key of gate2016. Suppose an insertion into candidate relation ... relation can cause inconsistency (c) Both operations can cause inconsistency of data (d) None of them can cause inconsistency of data
asked Aug 26 in Databases Maguluri Bhaskar 10 points 26 views
0 votes
0 answers 12 views
I knw the rules of view serializability but I want to check a schedule is view serializable or not using POLYGRAPH TEST. So, the given schedule is S:R1(X),W2(X),W1(X) ( link : https://gateoverflow.in/9429/problem-on-view-serializability ) Since ... polygraph, so the schedule is not view serializable. Kindly say is my approach about polygraph testing for view serializability is correct or not ?
asked Aug 26 in Databases user2525 1.5k points 12 views
0 votes
1 answer 11 views
For the following schedule, how many blind writes are possible ? My answer is total 3 blind writes are possible which I have marked above. Is it correct ?
asked Aug 26 in Databases user2525 1.5k points 11 views
0 votes
1 answer 23 views
https://gateoverflow.in/258022/dbms-basic-test1 Int the above question, as per the diagram, the leaves are supposed to be in level 4 and so the number of children in level 3 which equals to 27 as per calculation means the number of child pointers to level 4 that is the leaf node level is actually 27. Am I correct ?
asked Aug 23 in Databases user2525 1.5k points 23 views
0 votes
0 answers 16 views
For the below question, https://gateoverflow.in/285557/madeeasy-test-series-databases-b-tree Can anyone explain option B and option D ? I mean what they actually mean to say ?
asked Aug 23 in Databases user2525 1.5k points 16 views
0 votes
2 answers 30 views
The number of serial schedules which are view equal to schedule(s) but not conflict equal to schedule(s) are ________.
asked Aug 23 in Databases Abhinav999 8 points 30 views
1 vote
1 answer 40 views
When it comes to inserting something in a foreign key table, we cant put null values. But when it comes to deleting something from referenced table, we can perform ON DELETE SET NULL operation and make the foreign key value in a particular tuple as NULL. So, a foreign key can’t remain null while inserting but it can be null while deletion. Is my approach correct ?
asked Aug 21 in Databases user2525 1.5k points 40 views
0 votes
0 answers 5 views
Can someone write the entire steps and rules of polygraph test to check view serializability. P.S. : Kindly, dont give me links. Please write the rules in a stepwise manner if known.
asked Aug 21 in Databases user2525 1.5k points 5 views
0 votes
0 answers 12 views
Regarding statement Q, I don’t think it will violate 3NF because whatever be the R.H.S. if L.H.S. is superkey, then it is in BCNF and ultimately in 3NF. Therefore, it is allowed in 3NF and so the statement is supposed to be right. Is my approach correct ?
asked Aug 21 in Databases user2525 1.5k points 12 views
0 votes
0 answers 9 views
https://gateoverflow.in/208190/lossy-or-lossless In the above question : FDs are AB→C,AC→B,AD→E,B→D,BC→A,E→G. R1 ( ABC ) : AB → C AC → B BC → A R2 ( ACDE ) : AD → E R3 ( ADG ) has empty FDs. So, the above decomposition is not dependency preserving. But ... is AD a key order to check lossless decomposition ? Do we have 2 consider the closure of original fds to prove AD as key for R3 ( ADG ) ?
asked Aug 20 in Databases user2525 1.5k points 9 views
0 votes
0 answers 14 views
I know that BCNF may not satisfy dependency preserving but it should be lossless. So, when we are decomposing a relation for satisfying BCNF, we don’t care about the dependency preservation condition. But what about 3NF ? Is it compulsory to check for dependency preservation condition after a table has been decomposed to satisfy 3NF ?
asked Aug 20 in Databases user2525 1.5k points 14 views
0 votes
0 answers 6 views
In a file which contains 1 million records and the order of the tree is 100, then what is the maximum number of nodes to be accessed if B+ tree index is used? I need proper explanation I did not understood the answer of this question as it was already posted.
asked Aug 11 in Databases Aditya Anand 6 points 6 views
0 votes
1 answer 17 views
Kindly show the output also. Thank you.
asked Aug 4 in Databases DukeThunders 132 points 17 views
0 votes
0 answers 8 views
The answer is given 6. I am getting 6 too but I want to confirm the output. SID GATEID 12 101 12 104 15 101 16 103 25 102 27 NULL Am I correct?
asked Aug 4 in Databases DukeThunders 132 points 8 views
0 votes
1 answer 18 views
Consider the following relation: R (A1, A2, ….An) and every (n-2) attributes of R forms a candidate key. How many super keys are there in R?
asked Aug 4 in Databases DukeThunders 132 points 18 views
0 votes
0 answers 3 views
2PL generates serializability, but it does not prevent deadlocks. 2PL has 2 phases: growing and shrinking. Which of the following rules are used to govern the 2PL protocol? (a) 2 transactions cannot have conflicting locks (b) No unlock operation can precede a lock operation in the ... about C? What does it want to say? For option A, 2PL has deadlocks, so doesn't it mean it has conflicting locks?
asked Aug 4 in Databases DukeThunders 132 points 3 views
0 votes
0 answers 9 views
Choose the False statement: (a) time stamp protocol is deadlock free (b) 2- phase locking generates serializability (c) strict 2-phase locking is deadlock free (d) time stamp protocol may not result recoverable schedule
asked Aug 4 in Databases DukeThunders 132 points 9 views
0 votes
1 answer 22 views
0 votes
3 answers 32 views
Kindly show your solution. I am not able to decompose the relation. Thank you.
asked Aug 3 in Databases DukeThunders 132 points 32 views
0 votes
0 answers 6 views
Query1: SELECT eno FROM emp WHERE deptno=10 union SELECT eno FROM emp WHERE deptno=20 Query2: SELECT eno FROM emp WHERE deptno=10 or deptno=20 Let the result of Queryl is Q1 and the result of Query2 is Q2, then which of the following is always true? (A) Q1=Q2 (B) Q1 $\subseteq$ Q2 (C) Q2 $\subseteq$ Q1 (D) Data is insufficient
asked Jul 30 in Databases aditi19 29 points 6 views
0 votes
0 answers 3 views
Consider the following table the answer is there are two MVD in this relation Department ->>Part Department ->>Job how does the second MVD hold? d3 doesn’t have multiple values for job.
asked Jul 30 in Databases aditi19 29 points 3 views
0 votes
0 answers 3 views
This image is from NAVATHE book. for seconadry Index(in case of CK field) we can use sparse indexing as we do for PK, because every CK value is unique & it can uniquely identify each tuple. then what stops us from doing sparse indexing incase of CK field??? why NON-key row is Dense or Nondense in the image ??? for non-key we should always use dense indexing, isn’t it???
asked Jul 29 in Databases MRINMOY_HALDER 27 points 3 views
0 votes
2 answers 5 views
Consider the following schedule S of two transactions: r1(X), r2(Y), w1(Y), c1, w2(Z), c2. Tell whether S is serial? serializable? recoverable? ACR (avoids cascading rollback)? strict? Then, indicate which of the following is TRUE about S? a) S is ... recoverable and S is strict as per me there is no dirty read hence cascading rollbacks should be avoided . the schedule doesn't look strict either
asked Jul 22 in Databases TUSHAR_BHATT 12 points 5 views
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