These are framed exactly the way mid-sem questions are asked.
📘 6 Marks Important Questions & Answers
(Based on Merged PDF)
1) What are the Goals of a Distributed System? Explain. (6 Marks)
Answer:
The main goals of a Distributed System are:
Resource Sharing
Users can access remote hardware, software, and data resources.
Distribution Transparency
The system hides the distributed nature from users.
Openness
Uses standard protocols and interfaces for interoperability.
Scalability
System can grow in size, geographical area, and number of users.
Reliability and Fault Tolerance
System continues to function even if some components fail.
Concurrency
Multiple users can access shared resources simultaneously.
2) Explain Different Types of Distributed System Models. (6 Marks)
Answer:
Distributed systems are classified into:
1. Minicomputer Model
Multiple minicomputers connected by network.
2. Workstation Model
Each user has a workstation; idle workstations share resources.
3. Workstation-Server Model
Servers provide services like file, database, print.
4. Processor Pool Model
No home machine; processors are allocated dynamically.
5. Hybrid Model
Combination of workstation-server and processor pool.
3) Explain Data Independence and Transparency in DDBS. (6 Marks)
Answer:
Data Independence:
Ability to modify schema without affecting applications.
Logical Data Independence
Physical Data Independence
Transparency in DDBS:
Location Transparency
Fragmentation Transparency
Replication Transparency
Concurrency Transparency
Failure Transparency
Transparency makes distributed database appear as centralized.
4) Explain Horizontal and Vertical Fragmentation with Example. (6 Marks)
Answer:
Fragmentation divides database into smaller parts.
Horizontal Fragmentation:
Divides table by rows.
Example: EMPLOYEE table divided by region:
EMP_NORTH
EMP_SOUTH
Vertical Fragmentation:
Divides table by columns.
Example: EMP_PERSONAL (EmpID, Name) EMP_SALARY (EmpID, Salary)
Primary key must be included in each vertical fragment.
5) Explain Distributed Query Processing Steps. (6 Marks)
Answer:
Distributed Query Processing converts SQL query into execution plan across sites.
Steps:
Query Decomposition
Break query into relational algebra operations.
Data Localization
Replace global relations with fragments.
Global Optimization
Choose best strategy to minimize communication cost.
Local Optimization
Optimize operations at individual sites.
Goal: Reduce data transfer cost and response time.
6) Explain Two-Phase Commit Protocol (2PC). (6 Marks)
Answer:
2PC ensures atomicity in distributed transactions.
Phase 1: Prepare Phase
Coordinator sends “Prepare” message.
Participants reply Yes/No.
Phase 2: Commit Phase
If all Yes → Commit.
If any No → Abort.
Advantages:
Maintains consistency
Ensures atomicity
Disadvantage:
Blocking protocol
7) Explain Lamport Logical Clock Algorithm. (6 Marks)
Answer:
Logical clocks maintain event ordering.
Rules:
Increment clock before each event.
Send timestamp with message.
Receiver sets: Clock = max(local, received) + 1
Ensures happened-before relationship.
Used in distributed event ordering.
8) Explain Deadlock Detection in Distributed Systems. (6 Marks)
Answer:
Deadlock occurs when processes wait for each other indefinitely.
Techniques:
Centralized Detection One site maintains global wait-for graph.
Hierarchical Detection Detection responsibility divided among controllers.
Fully Distributed Detection Each site detects using partial information.
Deadlock recovery:
Abort one transaction
Resource preemption
9) Explain Replication Strategies in Distributed Database. (6 Marks)
Answer:
Replication means storing multiple copies of data.
Types:
Full Replication Entire database at every site.
Partial Replication Only selected data replicated.
Benefits:
High availability
Faster reads
Drawback:
Update synchronization complexity
10) Explain Mutual Exclusion Algorithms in Distributed Systems. (6 Marks)
Answer:
Mutual exclusion ensures only one process executes critical section.
Algorithms:
Centralized Algorithm Coordinator grants access.
Ricart-Agrawala Algorithm Timestamp-based permission.
Token Ring Algorithm Token circulates in ring structure.
Each has trade-off between message cost and fault tolerance.
🔥 If Your Mid-Sem is Theory-Based
Focus especially on:
2PC
Fragmentation
Query Processing
Logical Clock
Deadlock
Transparency
Replication
If you want, I can now:
📌 Prepare Unit-wise questions
📘 Make 10-mark long answers
📝 Create a full model question paper (with answers)
⚡ Give 1-day before exam revision notes
Tell me your syllabus units included in mid-sem.
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