In my post about consensus mechanisms, I had explained how miners on the network reach a consensus. This consensus is required for nodes to agree on the correct history of the chain. In all cases, only the longest chain is agreed to contain the correct history of transactions. Uncles and Orphans are two types of blocks which are created during race conditions between miners on the blockchain. This happens when two or more miners come up with a valid solution to a new block. In this case, the miner on the longer chain is allowed to add the block to the blockchain. Another type of block formed is the stale block, which must be explained before I tell you about uncles.

Stale Blocks

Stale blocks are those which are well-formed, but not included in the best chain. The best chain is the one which is agreed upon by all the nodes as the valid one. A stale block is formed when the blockchain is extended by the addition of another block before the former could be added to the chain. This happens due to propagation delays in the blockchain network. Upon mining a stale block, the miner is not rewarded any tokens. It is called a stale block, since the data has become old, according to the network.

Uncle Blocks

An uncle block, also called an “ommer” is a stale block specific to the Ethereum cryptocurrency. Unlike stale blocks found in cryptocurrencies such as Bitcoin, these are stale blocks which can be included in the chain, though at a later time. In fact, hashes of these uncle blocks are collated in future blocks. Another difference is that miners are paid to include these uncles in future blocks, although the amount decreases proportional to the longer it takes to add these uncles to the main chain. According to the creator of Ethereum, uncle blocks also reduce centralization risks by upto 85%.

Orphan Blocks

In a blockchain, each new block contains the hash of the previously added block. If a blockchain had n blocks, and the (n+1)th block is added, then the nth block is said to be the parent of the (n+1)th block. In an orphaned block, the “parent block hash” field points to an un-authenticated block that is detached from the blockchain. These blocks can be introduced by attackers or caused by race conditions during mining.

Enfin

Sometime ago, I had mentioned that mining pools are a way to earn cryptocurrencies using lower performance hardware. A few Ethereum mining pools also provide uncle rewards to miners of the pool. This post was aimed to eliminate the usual confusion between the three types of blocks. If this article helped you, please consider sharing a link to this page, so others can benefit too.

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