Empty blocks cause congestion in the Bitcoin network. Why do mining pools spend time mining empty blocks?

Bitcoin mining is an interesting topic that is sometimes difficult to understand without doing some research. One particular topic on the topic of mining is empty blocks, and people often wonder why Bitcoin mining pools have to mine them.

(Figure: Why Bitcoin mining pools must mine empty blocks )

Rediscussing the empty block

A Bitcoin mining pool is where a group of Bitcoin miners work together to find and verify block information every ten minutes. When a miner finds a specific block, most of the time the Bitcoin mempool fills up with transactions waiting to be confirmed. After successfully mining a block, the miner gets a reward of 12.5 BTC and all the fees associated with the specific block they found. In the early days, the blocks were not very full because Bitcoin was not as popular as it is today. Recently the block capacity has been full, often reaching the maximum limit of 1 MB.

Blocks filled with transaction information are not the only blocks mined in the network, as empty blocks are also mined. Empty blocks actually do have one transaction, called the coinbase, that is included first in every block. The main reason why Bitcoin mining pools mine empty blocks is that they perform mining operations non-stop. The concern about miners now is that mining empty blocks is causing the recent congestion on the Bitcoin network.

Non-stop Bitcoin mining

However, when a mining pool mines a block, it must download it and perform several functions in order to verify the transactions contained. At the same time, the mining pool is also receiving the next broadcast header (80 bytes of data attached to a block), and the mining pool begins working on its next block. Not only do miners invest time mining, they also have to take stock of blocks mined by competitors. Miners cannot stop to rest, they are constantly looking for as many blocks as possible.

It's like a NASCAR driver winning the Daytona 500 while also hoping to get the pole at Talladega seconds after finishing the Daytona race. Computer science professor and well-known Bitcoin user Jorge Stolfi gave a simple explanation for why a miner mines an empty block.

“Transaction fees are an incentive for bitcoin miners to include all the transactions that make it into their candidate blocks,” Stolfi explained. “However, a miner can often start mining a candidate for block N+1 before he’s seen anything included in block N. This is because he only needs the hash of block N, and he can often get it pretty quickly using a specific trick.”

In this case, the miner must start with an empty block N+1, even if there are transactions waiting in his queue, because he cannot check if these transactions are valid without knowing the content of block N. If he is lucky, he can solve this empty block N+1 even before he finishes downloading the body of block N. This is why there are always empty blocks.

Over 87,000 empty blocks

Empty blocks have been common since Bitcoin was created. For example, from the genesis block all the way to 360189, there have been 85,295 empty blocks on the blockchain. This means that from January 2009 to June 2015, approximately 23.68% of the blocks were empty. Mining an empty block is not the same work as filling up the maximum capacity. Since 2015, mining empty blocks has decreased. Some miners have stated that they do not mine empty blocks at all. Currently, the total transaction blocks mined to date are 87,885.

The idea that miners choose to mine empty blocks is true to a certain extent, but whether it is bad or not is another matter. The topic of empty blocks has been debated for years.