$1\mathrm{.}0$p$2$a

There are two transactions T$1$ and T$2$ for which the execution order of the individual operations look like this:

$$ T$1$: read$1($x$)$; read$1($y$)$; write$1($x$)$; write$1($y$).$

$$ T$2$: read$2($x$)$; write$2($x$).$

Here, x and y refer to different rows in the database. Assume that the read and write operations correspond to the following SQL queries, where x and y are refer to values of isbn, which is the primary key of the table Book.

read$1($x$)$:$$ SELECT titel FROM Boek WHERE isbn $=\text{'}0136067018\text{'}$;

read$1($y$)$: $$SELECT titel FROM Boek WHERE isbn $=\text{'}0321228383\text{'}$;

write$1($x$)$: UPDATE Boek SET titel $=$ titel $||\text{'}$ deel $1\text{'}$ WHERE isbn $=\text{'}0136067018\text{'}$;

write$1($y$)$: UPDATE Boek SET titel $=$ titel $||\text{'}$ deel $1\text{'}$ WHERE isbn $=\text{'}0321228383\text{'}$;

read$2($x$)$: $$SELECT titel FROM Boek WHERE isbn $=\text{'}0136067018\text{'}$;

write$2($x$)$: UPDATE Boek SET titel $=$ titel $||\text{'}$ deel $2\text{'}$ WHERE isbn $=\text{'}0136067018\text{'}$;

Answer the following questions:

$$

Which execution sequence$$ for the operations is a valid schedule of these transactions and serializable?

read$2($x$)$; read$1($x$)$; write$2($x$)$; read$1($y$)$; write$1($x$)$; write$1($y$)$;

write$1($x$)$; read$2($x$)$; read$1($x$)$; write$2($x$)$; read$1($y$)$; write$1($y$)$;

read$1($x$)$; read$1($y$)$; write$1($x$)$; read$2($x$)$; write$2($x$)$; write$1($y$)$;

write$2($x$)$; read$1($x$)$; read$1($y$)$; read$2($x$)$; write$1($x$)$; write$1($y$)$;

bookmark$\_$border$1\mathrm{.}0$p$2$b

We want to limit the concurrent execution of transactions T$1$ and T$2$ as little as possible, but in such a way that T$1$ will not do dirty reads. Select an isolation level for each transaction

T$1$: SERIALIZABLE

T$2$: SERIALIZABLE

T$1$: SERIALIZABLE

T$2$: READ UNCOMMITTED

T$1$: READ COMMITTED

T$2$: READ UNCOMMITTED

T$1$: READ COMMITTED

T$2$: SERIALIZABLE

$1$a

$1$b

$1$c

$1$d

$1$e

$1$f