Transactions

Question 1

a collection of several operations on the database appears to be a single unit from the point of view of the database user.

Answer 1

Transactions

Question 2

Collections of operations that form a single logical unit of work

Answer 2

Transactions

Question 3

is a unit of program execution that accesses and possibly updates various data items.

Answer 3

Transaction

Question 4

The “all-or-none” property of transactions

Answer 4

atomicity

Question 5

the database system
must take special actions to ensure that transactions operate properly without interference from concurrently executing database statements.

Answer 5

Isolation

Question 6

means that once a transaction is completed, its effects are permanent—they must survive system crashes.

Answer 6

Durability

Question 7

If the database starts in a valid state, it must still be valid after the transaction finishes.

Answer 7

Consistency

Question 8

Either all operations of the transaction are reflected properly in the database, or none are.

Answer 8

Atomicity

Question 9

Execution of a transaction in isolation (i.e., with no other transaction executing concurrently) preserves the consistency of the database.

Answer 9

Consistency

Question 10

Even though multiple transactions may execute concurrently, the system guarantees that, for every pair of transactions Ti and Tj, it appears to Ti that either
Tj finished execution before Ti started or Tj started execution after Ti finished.

Answer 10

Isolation

Question 11

After a transaction completes successfully, the changes it has made to the database persist, even if there are system failures.

Answer 11

Durability

Question 12

Thus, because of the failure, the state of the system no longer reflects a real state of the world that the database is supposed to capture.

Answer 12

inconsistent state

Question 13

Information does not usually survive system crashes.

Answer 13

Volatile storage

Question 14

Information survives system
crashes.

Answer 14

Non-volatile storage

Question 15

Information is never lost

Answer 15

Stable storage

Question 16

a transaction may not always complete its execution successfully.

Answer 16

aborted

Question 17

It is part of the responsibility of the recovery scheme to manage trans
action aborts.

Answer 17

Rolled back

Question 18

A file that records all database modifications before they are applied.

Answer 18

Log

Question 19

A transaction that completes its execution successfully

Answer 19

committed

Question 20

has performed updates transforms the database into a new
consistent state, which must persist even if there is a system failure.

Answer 20

committed

Question 21

The only way to undo the effects of a committed transaction

Answer 21

compensating transaction

Question 22

the initial state; the transaction stays in this state while it is executing.

Answer 22

Active

Question 23

after the final statement has been executed.

Answer 23

Partially committed

Question 24

after the discovery that normal execution can no longer proceed

Answer 24

Failed

Question 25

after the transaction has been rolled back and the database has been restored to its state prior to the start of the transaction.

Answer 25

Aborted

Question 26

after successful completion

Answer 26

Committed

Question 27

A trans action is said to have this if it has either committed or aborted.

Answer 27

terminated

Question 28

is considered to be a new transaction.

Answer 28

restart

Question 29

It usually does so because of some internal logical error that can be corrected only by rewriting the application program, or because the input was bad, or because the desired data were not found in the database.

Answer 29

Kill

Question 30

such as writes to a user’s screen, or sending email. Once such a write has occurred, it cannot be erased, since it may have been seen external to the database system.

Answer 30

observable external writes

Question 31

usually allow multiple transactions to run concurrently

Answer 31

Transaction-processing systems

Question 32

They represent the chronological order in which instructions are executed in the system.

Answer 32

schedules

Question 33

consists of a sequence of instructions from various transactions, where the instructions belonging to one single trans action appear together in that schedule.

Answer 33

serial

Question 34

A schedule that is equivalent to a serial schedule, meaning the final database state is the same as if the transactions ran one after another.

Answer 34

serializable

Question 35

A linear ordering of transactions that is consistent with the precedence graph

Answer 35

serializability order

Question 36

This phenomenon, in which a single transaction failure leads to a series of transaction rollbacks

Answer 36

cascading rollback.

Question 37

is a useful concept because it allows programmers to ignore issues related to concurrency when they code transactions.

Answer 37

Serializability

Question 38

usually ensures serializable execution

Answer 38

Serializable

Question 39

allows only committed data to be read and further requires that, between two reads of a data item by a transaction, no other transaction is allowed to update it.

Answer 39

Repeatable read

Question 40

allows only committed data to be read, but does not require repeatable reads.

Answer 40

Read committed

Question 41

allows uncommitted data to be read. It is the lowest isolation level allowed by SQL.

Answer 41

Read uncommitted

Question 42

It reads data from this private version and is thus isolated from the updates made by other transactions.

Answer 42

snapshot isolation

Question 43

a conflict may exist on “phan tom” data.

Answer 43

phantom phenomenon

Question 44

is often implemented using locks on index nodes

Answer 44

predicate locking