ISA 245 Final Exam With 100% Correct And Verified Answers
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ISA 245
ISA 245 Final Exam With 100% Correct And Verified Answers
Atomicity - Correct Answer-Requires that all operations (SQL requests) of a transaction be completed; if not, the transaction is aborted. If a transaction T1 has four SQL requests, all four requests must be successfully completed; other- wi...
ISA 245 Final Exam With 100% Correct
And Verified Answers
Atomicity - Correct Answer-Requires that all operations
(SQL requests) of a transaction be completed; if not, the
transaction is aborted. If a transaction T1 has four SQL
requests, all four requests must be successfully completed;
other- wise, the entire transaction is aborted. In other words,
a transaction is treated as a single, indivisible, logical unit of
work.
Concurrency control - Correct Answer-Coordinating the
simultaneous execution of transactions in a multiuser
database system is known as concurrency control.
The objective of concurrency control is to ensure the
serializability of transactions in a multiuser database
environment. Concurrency control is important because the
simultaneous execution of transactions over a shared
database can create several data integrity and consistency
problems. The three main problems are lost updates,
uncommitted data, and inconsistent retrievals.
Consistency - Correct Answer-indicates the permanence of
the database's consistent state. A transaction takes a
database from one consistent state to another. When a
transaction is completed, the database must be in a
consistent state; if any of the transaction parts violates an
integrity constraint, the entire transaction is aborted.
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,Consistent database state - Correct Answer-One in which all
data integrity constraints are satisfied. A successful
transaction changes the database from one consistent state to
another.
Database lock - Correct Answer-the entire database is
locked, thus preventing the use of any tables in the database
by trans- action T2 while transaction T1 is being executed.
This level of locking is good for batch processes, but it is
unsuitable for multiuser DBMSs.
Durability - Correct Answer-ensures that once transaction
changes are done and committed, they cannot be undone or
lost, even in the event of a system failure.
Exclusive lock - Correct Answer-exists when access is
reserved specifically for the transaction that locked the
object. The exclusive lock must be used when the potential
for conflict exists.
Field-level lock - Correct Answer-allows concurrent
transactions to access the same row as long as they require
the use of different fields (attributes) within that row.
Although field-level locking clearly yields the most flexible
multiuser data access, it is rarely implemented in a DBMS
because it requires an extremely high level of computer
overhead and because the row- level lock is much more
useful in practice.
Isolation - Correct Answer-means that the data used during
the execution of a transaction cannot be used by a second
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, transaction until the first one is completed. In other words, if
transaction T1 is being executed and is using
the data item X, that data item cannot be
accessed by any other transaction (T2 ... Tn)
until T1 ends. This property is particularly
useful in multiuser database environments
because several users can access and update
the database at the same time.
Lock - Correct Answer-guarantees exclusive
use of a data item to a current transaction. In
other words, transaction T2 does not have
access to a data item that is currently being
used by transaction T1.
Lock granularity - Correct Answer-Lock
granularity indicates the level of lock use.
Locking can take place at the following levels:
database, table, page,
row, or even field (attribute).
Lost update - Correct Answer-The lost update
problem occurs when two concurrent
transactions, T1 and T2, are updating the
same data element and one of the updates is
lost (overwritten by the other transaction)
Optimistic locking phases (3) - Correct
Answer-requires neither locking nor
timestamping techniques. Instead, a
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