Consider the following read-write schedule $S$ over three transactions $T_{1}$, $T_{2}$, and $T_{3}$, where the subscripts in the schedule indicate transaction IDs:
$S: r_{1}(z); w_{1}(z); r_{2}(x); r_{3}(y); w_{3}(y); r_{2}(y); w_{2}(x); w_{2}(y);$
Which of the following transaction schedules is/are conflict equivalent to $S$?
Suppose a database system crashes again while recovering from a previous crash. Assume checkpointing is not done by the database either during the transactions or during recovery.
Which of the following statements is/are correct?
Let ri(z) and wi(z) denote read and write operations respectively on a data item z by a transaction Ti. Consider the following two schedules.
S1 : r1(x) r1(y) r2(x) r2(y) w2(y) w1(x)
S2 : r1(x) r2(x) r2(y) w2(y) r1(y) w1(x)
Which one of the following options is correct?
![GATE CSE 2020 Database Management System - Transactions and Concurrency Question 7 English](https://imagex.cdn.examgoal.net/1da9i2ynkcu2d4qa/400c524c-3a46-4b39-babf-4f7b2b8996b6/2fc71120-ca49-11ea-b796-4745b429ed6f/file-1da9i2ynkcu2d4qb-500w.png)
Here, RX stands for “Read(X)” and WX stands for “Write(X)”. Which one of the following schedules is conflict equivalent to the above schedule?