Distributed ledger concept in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Distributed ledger concept

Transaction Created

↓

Transaction Broadcast

↓

Nodes Receive Transaction

↓

Nodes Validate Transaction

↓

Transaction Added to Ledger

↓

Ledger Updated Across Nodes

↓

Consensus Achieved

↓

End

This flow shows how a transaction is created, shared, validated, added to the ledger, and synchronized across all nodes to keep the ledger consistent.

Execution Sample

Blockchain / Solidity

transaction = {'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}
network.broadcast(transaction)
for node in network.nodes:
    if node.validate(transaction):
        node.ledger.append(transaction)
network.sync_ledgers()

This code simulates creating a transaction, broadcasting it to nodes, validating it, adding it to each node's ledger, and syncing ledgers.

Execution Table

Step	Action	Transaction State	Node Ledger State	Network State
1	Create transaction	{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}	[]	Transaction ready to broadcast
2	Broadcast transaction	{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}	[]	Transaction sent to all nodes
3	Node 1 validates	Valid	[]	Waiting to add transaction
4	Node 1 adds to ledger	Valid	[{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}]	Partial ledger updated
5	Node 2 validates	Valid	[]	Waiting to add transaction
6	Node 2 adds to ledger	Valid	[{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}]	Partial ledger updated
7	Sync ledgers	Valid	[{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}]	All ledgers synchronized
8	Consensus achieved	Valid	[{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}]	Ledger consistent across network

💡 All nodes have validated and added the transaction; ledgers are synchronized and consensus is reached.

Variable Tracker

Variable	Start	After Step 4	After Step 6	Final
transaction	None	{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}	{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}	{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}
Node 1 ledger	[]	[{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}]	[{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}]	[{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}]
Node 2 ledger	[]	[]	[{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}]	[{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}]
Network state	Idle	Transaction sent to all nodes	Partial ledger updated	Ledger consistent across network

Key Moments - 3 Insights

Why do all nodes need to validate the transaction before adding it to their ledger?

Each node must check the transaction to ensure it is valid and not fraudulent. This prevents bad data from entering the ledger, as shown in steps 3 and 5 where nodes validate before adding.

What happens if one node's ledger is different from others after adding a transaction?

The network syncs ledgers to keep them consistent, as seen in step 7. This synchronization ensures all nodes have the same ledger state, preventing conflicts.

Why is consensus important in a distributed ledger?

Consensus means all nodes agree on the ledger's content, ensuring trust and preventing fraud. Step 8 shows consensus achieved after synchronization.

Visual Quiz - 3 Questions

Look at the execution table, what is the state of Node 1's ledger after step 4?

A Transaction not added yet

B []

C [{'sender': 'Alice', 'receiver': 'Bob', 'amount': 10}]

D Ledger empty

💡 Hint

Check the 'Node Ledger State' column at step 4 in the execution_table.

At which step does the network synchronize all ledgers?

A Step 7

B Step 5

C Step 3

D Step 2

💡 Hint

Look for the action 'Sync ledgers' in the execution_table.

If Node 2 did not validate the transaction, what would happen to its ledger after step 6?

A It would include the transaction anyway

B It would remain empty

C It would crash

D It would sync automatically

💡 Hint

Refer to the 'Node Ledger State' and validation steps in the execution_table and variable_tracker.

Concept Snapshot

Distributed Ledger Concept:
- Transactions are created and broadcast to all nodes.
- Each node validates transactions independently.
- Valid transactions are added to each node's ledger.
- Ledgers are synchronized to keep data consistent.
- Consensus ensures all nodes agree on the ledger state.

Full Transcript

This visual execution shows how a distributed ledger works in a blockchain network. First, a transaction is created by a user. Then, it is broadcast to all nodes in the network. Each node receives the transaction and validates it to check if it is correct and not fraudulent. If valid, the node adds the transaction to its own ledger. After all nodes add the transaction, the network synchronizes the ledgers to make sure they all have the same data. Finally, consensus is reached when all nodes agree on the ledger's content, ensuring trust and consistency across the network.

Practice

1. What is the main purpose of a distributed ledger in blockchain technology?

easy

A. To store data only on one central computer

B. To share data across many computers to keep it safe and clear

C. To allow only one person to control the data

D. To make data unreadable for everyone

Solution

1. Step 1: Understand the concept of distributed ledger

   A distributed ledger shares data across many computers instead of one central place.

2. Step 2: Identify the main goal

   This sharing keeps data safe and clear for everyone involved.

3. Final Answer:

   To share data across many computers to keep it safe and clear -> Option B

4. Quick Check:

   Distributed ledger = shared safe data [OK]

Hint: Distributed means data is shared, not stored in one place [OK]

Common Mistakes:

• Thinking data is stored on a single computer
• Believing one person controls the ledger
• Confusing encryption with data sharing

2. Which of the following is the correct way to describe a block in a distributed ledger?

easy

A. A software program that controls the network

B. A single piece of data stored only on one computer

C. A secret key used to encrypt data

D. A group of transactions linked together and shared across the network

Solution

1. Step 1: Define what a block is in blockchain

   A block is a group of transactions bundled together.

2. Step 2: Understand its role in the network

   Blocks are linked and shared across the network to keep data consistent.

3. Final Answer:

   A group of transactions linked together and shared across the network -> Option D

4. Quick Check:

   Block = grouped shared transactions [OK]

Hint: Blocks group transactions and share them across the network [OK]

Common Mistakes:

• Thinking a block is just one piece of data
• Confusing blocks with encryption keys
• Believing blocks are software programs

3. Consider a simple blockchain network where each block contains a hash of the previous block. If the first block's hash is 'abc123', and the second block's hash is calculated as hash('abc123' + 'data2'), what happens if someone tries to change 'data2' in the second block?

medium

A. The first block's hash changes automatically

B. Nothing changes because hashes are not linked

C. The hash of the second block changes, breaking the chain

D. The network ignores the change and continues

Solution

1. Step 1: Understand hash linking in blocks

   Each block's hash depends on the previous block's hash and its own data.

2. Step 2: Effect of changing data in second block

   Changing 'data2' changes the second block's hash, which breaks the chain's integrity.

3. Final Answer:

   The hash of the second block changes, breaking the chain -> Option C

4. Quick Check:

   Changing data breaks hash chain [OK]

Hint: Changing block data changes its hash, breaking the chain [OK]

Common Mistakes:

• Thinking hashes are independent
• Believing first block changes automatically
• Assuming network ignores hash mismatches

4. A developer wrote this pseudocode for adding a new block to a distributed ledger:

function addBlock(data) {
  previousHash = getLastBlockHash()
  newHash = hash(data)
  block = { data: data, previousHash: previousHash, hash: newHash }
  ledger.append(block)
}

What is the main error in this code?

medium

A. The new hash should include the previous hash, not just data

B. The previous hash should be ignored when adding a block

C. The block should not store the previous hash

D. The ledger should be cleared before appending

Solution

1. Step 1: Review how block hashes are calculated

   A block's hash must include the previous block's hash and its own data to link blocks securely.

2. Step 2: Identify the mistake in hash calculation

   The code only hashes the data, missing the previous hash, breaking the chain security.

3. Final Answer:

   The new hash should include the previous hash, not just data -> Option A

4. Quick Check:

   Hash must include previous hash + data [OK]

Hint: Hash must combine previous hash and data to link blocks [OK]

Common Mistakes:

• Hashing only data without previous hash
• Ignoring previous hash in block structure
• Clearing ledger unnecessarily

5. You want to design a distributed ledger system where multiple participants can add transactions, but only valid transactions are accepted after consensus. Which approach best ensures data integrity and trust in this system?

hard

A. Use a consensus algorithm that requires agreement from most participants before adding a block

B. Allow any participant to add blocks without checks to speed up the process

C. Store the ledger on a single trusted server controlled by one participant

D. Encrypt all transactions so no one can see the data

Solution

1. Step 1: Understand consensus in distributed ledgers

   Consensus algorithms require most participants to agree on the data before adding it, ensuring trust.

2. Step 2: Evaluate options for data integrity and trust

   Allowing unchecked additions or central control reduces trust; encryption alone doesn't ensure consensus.

3. Final Answer:

   Use a consensus algorithm that requires agreement from most participants before adding a block -> Option A

4. Quick Check:

   Consensus ensures trust and data integrity [OK]

Hint: Consensus means most agree before adding data [OK]

Common Mistakes:

• Skipping consensus to speed up adding blocks
• Centralizing ledger storage
• Relying only on encryption without consensus