What Is a Blockchain Reorganization? 🔄🔗
A blockchain reorganization (reorg) happens when a network changes which recent chain history it considers canonical.
1️⃣ Two Blocks Appear
Sometimes, competing blocks can be produced around the same time.
Different nodes may temporarily see different versions of the chain.
2️⃣ Nodes Follow Their Protocol Rules
The blockchain's consensus rules determine which chain should be followed.
3️⃣ One History Becomes Canonical
The network converges on one chain, while blocks that are no longer part of that chain become stale, orphaned, or otherwise non-canonical, depending on the protocol.
4️⃣ What Happens to Transactions?
Transactions from a replaced block may:
✅ Already exist in the new canonical chain
🔄 Return to the pending pool
❌ Become invalid if they conflict with the accepted chain state
🧠 Key Idea
A reorganization doesn't necessarily mean the blockchain was hacked.
It can be a normal consequence of distributed networks, especially when blocks are produced close together.
Temporary disagreement → Consensus rules → Canonical chain → Network continues
Understanding reorgs also explains why confirmations and finality matter.
Next: What is a blockchain transaction pool (mempool), and where does a transaction wait before entering a block? 📦
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