List of top Database Management Systems Questions on Transactions and concurrency control

Let $R(z)$ and $W(z)$ denote read and write operations on a data element $z$ by a transaction $T_i$, respectively. Consider the schedule $S$ with four transactions.
\[ S: R_1(x) R_2(x) R_3(y) W_1(y) W_2(x) W_3(y) R_4(y) \] Which one of the following serial schedules is conflict equivalent to $S$?

Let $S$ be the following schedule of operations of three transactions $T_1, T_2$ and $T_3$ in a relational database system:
\[ R_2(Y),\; R_1(X),\; R_3(Z),\; R_1(Y),\; W_1(X),\; R_2(Z),\; W_2(Y),\; R_3(X),\; W_3(Z) \] Consider the statements $P$ and $Q$ below:
\[ P:\ S \text{ is conflict-serializable.} \] \[ Q:\ \text{If } T_3 \text{ commits before } T_1 \text{ finishes, then } S \text{ is recoverable.} \] Which one of the following choices is correct?

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 $ r_i(z) $ and $ w_i(z) $ denote read and write operations respectively on a data item $ z $ by a transaction $ T_i $. Consider the following two schedules.
\[ \begin{aligned} S_1 &: r_1(x)\; r_1(y)\; r_2(x)\; r_2(y)\; w_2(y)\; w_1(x) \\ S_2 &: r_1(x)\; r_2(x)\; r_2(y)\; w_2(y)\; r_1(y)\; w_1(x) \end{aligned} \] Which one of the following options is correct?