Exam (elaborations)
UTA INSY 3304 – CHAPTER 10 EXAM
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UTA INSY 3304 – CHAPTER 10 EXAM...
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Transaction - ANSWER A logical unit of work that must be entirely completedor aborted
Atomicity - ANSWER All operations of a transaction must be completed; if not
the transaction is aborted
Consistency - ANSWER Permanence of database's consistent state
Isolation - ANSWER Data used during a transaction cannot be used by the
second transaction until the first is completed
Durability - ANSWER Ensures that once transactions are committed they
cannot be undone or lost
Serializability - ANSWER Ensures that the schedule for the concurrent
execution of several transactions should yield consistent results
Transaction Log - ANSWER Keeps track of all transactions that update the
database
DBMS uses the information stored in a log for (a):
- Recovery requirement triggered by a ROLLBACK statement
- Program's abnormal termination
- System failure
Concurrency Control - ANSWER Coordination of the simultaneous transactions
execution in a multiuser database system
• Objective: ensures serializability of transactions in a multiuser database
environment
Problems in Concurrency Control - ANSWER Lost update, uncommitted data,
inconsistent retrievals
, Scheduler - ANSWER Establishes the order in which the operations are
executed within concurrent transactions
- Creates serialization schedule
Locking methods - ANSWER facilitate isolation of data items used in
concurrently executing transactions
Lock - ANSWER guarantees exclusive use of a data item to a current
transaction
Pessimistic locking - ANSWER use of locks based on the assumption that
conflict between transactions is likely
Lock manager - ANSWER responsible for assigning and policing the locks used
by the transactions
Lock Granularity - ANSWER - indicates level of lock use
- levels: database, table, page, row, or field (attribute)
Binary lock - ANSWER A lock that has only two states: locked (1) and
unlocked (0). If a data item is locked by a transaction, no other transaction can
use that data item.
Exclusive lock - ANSWER Access is reserved for the transaction that locked
the object
Shared lock - ANSWER Concurrent transactions are granted read access on the
basis of a common lock
Problems using locks - ANSWER - resulting transaction schedule might not be
serializable
- schedule might create deadlocks
Two-Phase Locking to Ensure Serializability - ANSWER Defines how
transactions acquire and relinquish locks
• Guarantees serializability but does not prevent deadlocks
Phases
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