Clear DefinitionsEmpty Block Mining
3 min read
Pronunciation
[emp-tee blok mahy-ning]
Analogy
Think of empty block mining as a bus driver who, upon arriving at a stop and seeing passengers waiting, decides to depart immediately without picking anyone up in order to maintain schedule and receive their paycheck. While the driver still performs the route (solving the cryptographic puzzle) and gets paid (block reward), no actual service is provided to waiting passengers (pending transactions). The driver does this because taking the time to board passengers might allow another driver to complete the route first and claim the paycheck.
Definition
The practice of creating and submitting valid blocks that contain no transactions (other than the coinbase transaction that rewards the miner) to a blockchain network. Empty block mining occurs when miners prioritize speed over transaction inclusion to gain block rewards and minimize validation overhead, potentially reducing a network's effective transaction throughput.
Key Points Intro
Empty block mining involves four key aspects that affect blockchain network operation and economics.
Key Points
Reward Prioritization: Miners optimize for receiving block rewards without the additional computational overhead of transaction verification.
Latency Advantage: Skipping transaction inclusion and verification gives miners a time advantage in propagating new blocks after receiving the previous block.
Network Impact: Reduces effective transaction throughput and can increase congestion during high-demand periods.
Protocol Incentives: Results from misaligned incentives where block rewards outweigh transaction fee revenue or where verification costs exceed fee income.
Example
A Bitcoin mining pool receives a new valid block from the network and immediately begins mining on top of it. Rather than taking time to collect and verify pending transactions from the mempool, the pool starts mining an empty block containing only the coinbase transaction (which provides the 6.25 BTC block reward). This gives them a head start of several seconds over competitors who are assembling transaction-filled blocks. When the pool successfully mines a block, they receive the full block reward despite not processing any user transactions. Users waiting for transaction confirmations must wait for the next block, effectively reducing the network's throughput during that block interval.
Technical Deep Dive
Empty block mining exploits the minimal validation requirements of proof-of-work blockchains, where a block needs only a valid proof-of-work solution and properly structured header to be accepted by the network, regardless of transaction content. Miners employ various techniques to optimize the empty block mining process, including header-only mining where work begins immediately after receiving the previous block's header, before its full contents are verified. Some implementations use specialized templates with pre-computed coinbase transactions to minimize startup latency. The economic calculus for empty block mining considers several factors: block reward value, available transaction fees, transaction verification computational cost, orphan risk (probability of being outcompeted during verification time), and propagation advantage (time saved by transmitting smaller blocks). In many proof-of-work networks, the pure block reward significantly exceeds transaction fees during normal operation, creating economic incentives that may favor empty block mining, particularly for miners with less competitive hash power who benefit more from the head start. Some protocols have implemented countermeasures including minimum transaction requirements, graduated reward structures based on block fullness, or transaction-dependent proof-of-work that integrates transaction verification into the mining process itself.
Security Warning
While empty block mining itself doesn't directly compromise security, excessive empty blocks can create transaction backlogs that may increase vulnerability to certain denial-of-service attacks. During high congestion periods, monitor your transaction fees carefully, as empty blocks can exacerbate fee spikes.
Caveat
While often criticized, empty block mining isn't necessarily malicious and can result from rational economic decisions by miners. In some cases, empty blocks may occur due to technical reasons such as network propagation delays or software limitations rather than deliberate strategy. The prevalence of empty block mining tends to shift with network economics—as block rewards decrease through halvings and transaction fees become a larger portion of miner revenue, the incentive to include transactions generally increases. Additionally, some mining operations may mine empty blocks only in specific circumstances, such as immediately after receiving a new block, rather than as a consistent strategy.
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