Lecture-1.1 PDC

-

### Synchronous Communication

1. **Definition**: In synchronous communication, components work in a coordinated way with a set order and timing. Here, the sender waits until the receiver confirms receipt before continuing.

   

2. **Characteristics**:

   - **Real-Time Interaction**: The sender waits for the receiver’s reply before moving forward.

   - **Request-Response Pattern**: A request is sent, and the sender pauses until a response comes back.


3. **Advantages and Disadvantages**:

   - **Simplified Design**: It’s easy to design since processes are in sync, knowing exactly what’s happening when.

   - **Potential Delays**: If the receiver takes time to respond, the sender is idle, which can slow down the system.


4. **Example**: 

   Imagine a **chat system** where every message you send has to be acknowledged by the other person immediately before you can send the next message. If the other person delays, you’re left waiting.


---


### Asynchronous Communication

1. **Definition**: In asynchronous communication, processes don’t wait for each other. The sender doesn’t need a reply right away and continues without delay.

   

2. **Characteristics**:

   - **Independent Operations**: Processes can continue their tasks without stopping for responses.

   - **Event-Driven**: Actions happen in response to events, and responses come whenever they’re ready, without set timing.


3. **Advantages and Disadvantages**:

   - **Responsiveness and Scalability**: Faster as each component can operate freely. It’s also better suited for distributed systems as processes don’t depend on immediate replies.

   - **Complexity**: Handling responses out of order and ensuring data is consistent can be challenging.


4. **Example**:

   In an **email system**, you send an email without expecting an immediate response. The other person replies when they’re available, and you continue your work without waiting.


---


### Comparison in Distributed Systems

In distributed systems, choosing between synchronous and asynchronous approaches depends on your needs:


- **Performance**: Synchronous communication might slow things down due to wait times, while asynchronous can speed up tasks by allowing parallel processes.

- **Fault Tolerance**: Asynchronous communication improves fault tolerance since components aren’t directly dependent on each other’s responses.

- **Complexity**: Synchronous is simpler in structure, while asynchronous needs extra care with data management due to possible delays or reordering of messages.

- **Scalability**: Asynchronous setups are often more scalable, enabling multiple processes to run concurrently, utilizing resources effectively.


---


### Example Scenarios of Data Replication


#### Synchronous Replication

When you **write data to a master server**, it saves it and sends it to all replicas. The master only acknowledges your write request once all replicas confirm receiving the data. If even one replica fails, the whole system can’t proceed, ensuring **strong data consistency** but causing possible delays.


- **Downside**: The slowest replica or network link dictates the speed of the whole operation.

- **Failure Case**: If a replica becomes unavailable, the master stops taking writes, only allowing reads.


#### Asynchronous Replication

Here, the client gets confirmation as soon as the master records the data; replicas receive it later. This method provides **quick responses**, but if the master fails before updates reach all replicas, some data could be lost.


- **Downside**: Some data might be lost if there’s a failure, as replicas are not updated instantly.


#### Semi-Synchronous Replication

This is a **hybrid** approach: the master server waits for at least one replica to confirm the data before acknowledging the write. This balances consistency with better speed than full synchronous replication.


- **In a Single Replica Setup**: It acts like synchronous replication.


---


### Key Takeaways

1. **Synchronous Communication**: Waits for responses, ensuring coordination but may slow down processes.

2. **Asynchronous Communication**: No need for waiting; faster and more scalable, but handling consistency requires extra effort.

3. **Replication Methods**:

   - Synchronous: Ensures full data consistency but might delay operations.

   - Asynchronous: Quick but with less consistency.

   - Semi-Synchronous: Balances speed and reliability.


This gives you a full view of synchronous and asynchronous concepts for your exam. Feel free to ask for more clarification on any part!

Comments

Post a Comment

Popular posts from this blog

SE

-
  SDLC Models in Detail: 1. Waterfall Model: - This is the basic/classic SDLC model - The phases happen in a strict linear sequence - requirements, design, implementation, testing, deployment, maintenance - Each phase must be completed fully before moving to the next phase - It is like a "waterfall" of progress flowing steadily downwards - Easy to understand and use, but very rigid and no room for revisions once a phase is over 2. Iterative Waterfall Model:  - Provides a feedback path to previous phases to allow changes/revisions - For example, if an issue is found in testing, you can loop back and rework the design - More flexible than the basic waterfall, but still quite rigid and sequential 3. Incremental Model: - The product is built and delivered in incremental releases - For example, an email app may release basic emailing first, then add calendaring, contacts, etc. in later increments   - Each increment goes through the full SDLC cycles - Allows faster deliver...
Read more

2.16 - 2.20

-
2.16 **Evolution of C++:** - Bjarne Stroustrup at Bell Laboratories made the first modifications to C in 1980, adding features from Simula 67 and Smalltalk. - These modifications included classes, derived classes, public/private access control, constructor and destructor methods, etc., resulting in "C with Classes" in 1983. - In 1984, virtual methods, method name and operator overloading, and reference types were added, resulting in C++. - The Cfront implementation of C++ appeared in 1985, followed by further evolutions leading to Release 2.0 in 1989 and Release 3.0 in 1990. - Key additions included multiple inheritance, abstract classes, templates, and exception handling. **Language Overview:** - C++ supports both procedural and object-oriented programming, with functions and methods. - Operators and methods can be overloaded, and dynamic binding is achieved through virtual methods. - Templated methods and classes allow for parameterization. - Multiple inheritance is support...
Read more

Synchronization

-
Image
1. **Synchronization Hardware:**    - Imagine you have a group project where each team member needs to work on a specific part simultaneously. Synchronization hardware ensures that everyone knows when to start and finish their task, preventing chaos and ensuring smooth collaboration. 2. **Atomic Operations:**    - Think of atomic operations as a "do not disturb" sign on a door when someone is inside doing something important. It guarantees that either the entire task is completed successfully, or none of it happens at all, avoiding halfway-done tasks and maintaining consistency. 3. **Memory Barriers and Fences:**    - Picture a bulletin board where everyone posts updates and announcements. Memory barriers and fences act like moderators, making sure that everyone sees the updates in the correct order and preventing misunderstandings or outdated information. 4. **Cache Coherence Protocols:**    - Imagine you and your friends have copies of the same ...
Read more