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Recent questions tagged transaction-and-concurrency

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181

Syllabus of Database management system
Are following part of gate syllabus for dbms? 1-Validation Based protocols 2-multiversion schemes 3-snapshot isolation 4-predicate reads(concurrency control) 5-concurrency in index structures.

bts1jimin asked in Databases Aug 27, 2018

880 views

1 vote

1 answer

182

Transaction & Concurrency control
Which of the following statement is/are incorrect? A: A schedule following strict two phase locking protocol is conflict serializable as well as recoverable. B: Checkpoint in schedules are inserted to ensure recoverability. (A) Only 1 (B) Only 2 (C) Both 1 and 2 (D) None

Verma Ashish asked in Databases Aug 25, 2018

by Verma Ashish

1.6k views

3 votes

4 answers

183

MADE EASY TEST SERIES
Consider the following schedules involving two transactions. $S_1 : R_1(x), W_2(y),R_2(x),W_1(y), \ commit_1, \ commit_2$ $S_2 : R_1(x), R_2(y),W_1(z), \ commit_1,R_3(y), R_3(z), W_2(y), W_3(x), commit_2, commit_3$ Which of the following ... S2 are allowed under 2PL B) only S1 is allowed under 2PL C) only S2 is allowed under 2PL D) neither S1 nor S2 is allowed under 2PL

syncronizing asked in Databases Aug 19, 2018

by syncronizing

1.8k views

0 votes

0 answers

184

Test Series
Question: Consider the following transactions: The number schedules of T1 and T2 recoverable are ________.

syncronizing asked in Databases Aug 19, 2018

by syncronizing

365 views

0 votes

2 answers

185

SELF DOUBT
T(1) T(2) R(A) W(A) W(A) SUPPOSE WE HAVE TWO TRANSACTION T1 AND T2. AND ALSO INTIAL VALUE OF A IS 100. THEN WE FIRST READ A AND THEN FROM T(2) WRITE A . SO MY DOUBT IS WHEN I AM WRITING A WITHOUT ANY CONDITION SPECIFYING . WHAT DOES IT MEAN ???? WHETHER A IS GOING TO CHANGE TO ANY VALUE AND WE DONT CONDITION OR IT IS JUST WRITING A VALUE WHICH IS 100. I AM NOT GETTING THIS CONCEPT .

Deepanshu asked in Databases Aug 18, 2018

298 views

2 votes

2 answers

186

Databases
State true or false: a schedule has only constrained write operations and the schedule is view serializable then it's also conflict serializable

Ajaaz asked in Databases Aug 6, 2018

by Ajaaz

322 views

0 votes

1 answer

187

Timestamp Ordering Protocol
Suppose that transaction Ti issues write(Q). According to timestamp Ordering protocol: If TS(Ti)<R-timestamp(Q) then Ti will rollback. My doubt is if TS(Ti) < R-timestamp(Q),it means write operation is occurring before the read operation and ... the transaction is reading the correct value of Q.Then why is it rolling back? Please correct me where am I going wrong.

Bhagyashree Mukherje asked in Databases Jul 28, 2018

by Bhagyashree Mukherje

1.2k views

1 vote

1 answer

188

Two Phase Locking
How 2PL guarenteed serializability? I think conflict serializability is not guarenteed for 2PL. But may be view serializable Plz explain it

srestha asked in Databases Jul 28, 2018

958 views

1 vote

0 answers

189

2PL Protocol
Consider the following schedules involving two transactions. Which of the following statements is true? A. Both S1 and S2 are allowed under 2PL. B. Only S2 is allowed under 2PL. C. Only S1 is allowed under 2PL. D. Neither S1 nor S2 allowed under 2PL.

Na462 asked in Databases Jul 14, 2018

by Na462

762 views

1 vote

1 answer

190

Serializability

Na462 asked in Databases Jul 14, 2018

by Na462

720 views

0 votes

1 answer

191

UGC NET CSE | July 2018 | Part 2 | Question: 65
Consider the following schedules involving two transactions. $S_1 : r_1(X) ; r_1(Y); r_2(X); r_2(Y); w_2(Y); w_1(X)$ $S_2 : r_1(X) ; r_2(X); r_2(Y); w_2(Y); r_1(Y); w_1(X)$ Which one of the following statements is correct ... not conflict serializable $S_1$ is not conflict serializable and $S_2$ is conflict serializable

Pooja Khatri asked in Databases Jul 13, 2018

by Pooja Khatri

1.2k views

0 votes

1 answer

192

Two phase locking and time stamp
Which of the following is correct ? I.Two phase locking is an optimistic protocol. II. Two phase locking is pessimistic protocol III. Time stamping is an optimistic protocol. IV. Time stamping is pessimistic protocol. A I and III B II and IV C I and IV D II and III

bts asked in Databases Jun 30, 2018

by bts

1.1k views

0 votes

0 answers

193

self doubt
i didn't understand the concept of view serializability can i skip this topic for the exam ? although i thing it had never asked in gate exam too.

vijju532 asked in Databases Jun 23, 2018

140 views

0 votes

2 answers

194

Dirty Read
The Transaction : - T1 T2 R(a) W(a) R(a) C C The above shown schedule is not Dirty read Right ?

Na462 asked in Databases Jun 2, 2018

by Na462

458 views

8 votes

1 answer

195

Are aborted transactions ALWAYS ignored when determining result/view/conflict serializability?
I am looking for some clarity on this topic. Here is some random schedule as an example: $r1(x) w1(x) r2(x) w2(x) r3(y) r3(x) w3(x) c3 a1 c2$ I was told, that for ... , strictness or avoidance of cascading rollbacks. I would be grateful if the question would be answered since this really confuses me.

flow2539 asked in Databases May 28, 2018

2.7k views

1 vote

0 answers

196

Understanding multiversion timestamp ordering protocol in database systems
I was reading multiversion timestamp ordering protocol from the book Database Systems Concepts by Korth. It can be explained in simpler words as follows: Each data item version $Q$ has two timestamps associated with it: W-timestamp: ... I am wrong and it was indeed asked in previous year GATE paper?) Can we safely skip it?

GateAspirant999 asked in Databases May 21, 2018

by GateAspirant999

2.8k views

0 votes

2 answers

197

MadeEasy Test Series: Databases - Transactions
Consider the following schedule: How many serial schedules view equal to schedule (S)? Answer: 10 Approach Please??

Na462 asked in Databases May 18, 2018

by Na462

433 views

1 vote

2 answers

198

Transaction 1
How many concurrent schedules are conflict serializable of given transactions T1 and T2:

Na462 asked in Databases May 12, 2018

by Na462

403 views

0 votes

1 answer

199

Madeeasy workbook
Q-25.

Avik Chowdhury asked in Databases May 9, 2018

by Avik Chowdhury

180 views

1 vote

3 answers

200

ISRO2018-55
Let us assume that transaction $T1$ has arrived before transaction $T2$. Consider the schedule $s=r1(A);r2(B): w2(A); w1(B)$ Which of the following is true? Allowed under basic timestamp protocol. Not allowed under basic timestamp protocols because $T1$ is rolled back. Not allowed under basic timestamp protocols because $T2$ is rolled back. None of these

Arjun asked in Databases Apr 22, 2018

by Arjun

5.4k views

2 votes

1 answer

201

No of Schedules
Given, Transaction T1 has n operation Transaction T2 has m operation Prove that, the total number of schedules possible is $\frac{(m+n)!}{m!n!}$

hacker16 asked in Databases Apr 13, 2018

533 views

1 vote

1 answer

202

Dirty Read
Correct me where i am wrong if i am wrong Please :) Dirty Read means Reading the data of uncommited transaction. For removing the Dirty read we should always read after the transaction which wrote X commits , this is the only way to remove dirty read rt ? T1 T2 ... (x) Above Shown is The Only way of removing the Dirty read rt ? My doubt is its very similar to the Solution of Cascadeless.

Na462 asked in Databases Apr 12, 2018

by Na462

891 views

1 vote

1 answer

203

Transaction
how view serializability ensures serial schedule?? i mean in view we leave many conflict like RW,WW,......we only talks about WR conflict and intial read and final write. then how it ensurs serailizability??

Ravi prakash pandey asked in Databases Apr 10, 2018

by Ravi prakash pandey

183 views

0 votes

2 answers

204

Uttrakhand Asst. Professor Exam-15
The basic properties of transaction is called ACID property RAW property BEEM property None of the above

gatecse asked in Unknown Category Mar 2, 2018

199 views

1 vote

1 answer

205

Cascadeless/ Recoverable
The given schedule: R1 (A) R2 (B) W2 (B) W1(A) W2 (A) Commit2 R1 (C) is revoreable, cascadeless or strict?

budhu asked in Databases Jan 29, 2018

by budhu

1.1k views

2 votes

0 answers

206

Ace Test Series: DBMS - Transaction And Serializablity
Answer given is 24 which is the no. of serial schedules possible, but my doubt is since no two transactions share same variables then all the schedules possible will be conflict serializable then why only serial schedules are considered ?

ashish pal asked in Databases Jan 26, 2018

335 views

1 vote

0 answers

207

transaction
r1(X),W2(X),c2(2 is committed),r1(X) I know that the precedence graph of this will not contain cycle. But i have not understood why. Its happenning. if X=100 then T1 read X as 100 then T2 comes and makes it 200 and then T2 is committed Then T1 reads it it ... ;T2, therefore read operation of T1 will be X=100 at the end but its new value is 200, so why we are not taking cycle in this.

Aman Bisht 1 asked in Databases Jan 25, 2018

by Aman Bisht 1

161 views

1 vote

1 answer

208

Self Doubt about Dirty Read and Recoverable
I can't exactly identify when a transaction has dirty read problem and when it doesn't. Take the following instances 1. S:T2r(x);T3r(x);T3 commit;T2 commit This is not dirty read as there is no write operation performed by either ... T2 this is recoverable. This is what I think regarding the above schedules. Is this right or is it only "JUGAAD"?

_jerry asked in Databases Jan 24, 2018

by _jerry

903 views

2 votes

0 answers

209

Concurrency Control
Which of the following statement is true? 1. time stamp protocol may not result recoverable schedule 2. in 2PL, No data are affected until all locks are obtained i.e., until the transaction is in its locked point. a) only a b) only b c) a and b d) none

hacker16 asked in Databases Jan 18, 2018

972 views

2 votes

1 answer

210

concurrent , nonserial ,serial
1)concurrent schedules= nonserial+serial 2)concurrent = nonserial schedules. which is correct terminology ?

gari asked in Databases Jan 18, 2018

by gari

207 views

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Recent questions tagged transaction-and-concurrency