CSE 511 – Midterm Exam Questions With
Verified And Updated Answers
Transaction - answer✔User program that can either read or write data from or to the database
system
ACID - answer✔Atomicity, Consistency, Isolation and Durability
ACID - Atomic - answer✔All or nothing - Transaction must be completed in full or not at all (no
subdividing)
ACID - Consistency - answer✔Transactions will transform the database from one consistent
state to another. There are no violations of integrity constraints.
ACID - Isolated - answer✔Transactions execute independently of one another. Database
changes are not revealed to one another until after a transaction has completed.
Serializable - even if some transactions are executed concurrently the results must be the same
as if they were executed serially in some order.
ACID - Durable - answer✔Database changes are permanent.
How is concurrency achieved in DBMS? - answer✔Interleaving actions of multiple transactions.
Serial Schedule - answer✔Schedule that does not interleave the actions of different
transactions.
Equivalent Schedule - answer✔Effect of executing the first schedule is identical to the effect of
executing the second schedule.
Serializable Schedule - answer✔A schedule that is equivalent to some serial execution of the
transaction.
Two schedules are conflict equivalent if: - answer✔- Schedules involve the same actions of the
same transactions
ALL RIGHTS RESERVED.
- Every pair of conflicting actions (read/write conflict) is ordered the same way
Conflict Serializable Schedule - answer✔Schedule S is conflict serializable if S is conflict
equivalent to some serial schedule.
Creating dependency graph to determine if transactions are conflict serializable - answer✔-
Create one node per transaction (e.g. Ti, Tj)
-Create an edge from Ti to Tj if Tj reads/writes an object last written by Ti
-Examine the graph for cycles. If a cycle exists then the set of transactions is NOT conflict
serializable
Strict Two Phase Locking - answer✔A transaction must acquire a shared lock on an item before
reading and an exclusive lock on an item before writing.
-Multiple transactions may hold a shared lock on a single item.
-If a transaction holds an exclusive lock on an item no other transaction may hold a
shared/exclusive lock on that same item.
Define the two phases of Strict 2PL - answer✔Phase One: transaction will acquire locks that it
needs
Phase Two: transaction will release locks at the end of the transaction
What is the lock manager? - answer✔The lock manager handles lock and unlock requests.
These operations are atomic.
What is deadlock and how do we detect it? - answer✔Cycle of transactions waiting for locks to
be released by one another.
We can detect a deadlock by creating a wait-for graph:
-Nodes are transactions
-Create an edge from Ti to Tj if Ti is waiting for Tj to release a lock (Tj holds exclusive lock on
object that Ti needs access to)
-If cycle exists there is a deadlock
Shared vs Exclusive Lock - answer✔Shared lock: required to read from an object
Exclusive lock: required to write to an object
Types of Failures: Transaction, System, Media, Communication - answer✔-Transaction:
transaction is aborted (~3% abort abnormally)
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