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Sharding and the Future of Blockchains

Blockchain sharding could potentially solve the greatest long-term threat to the viability of blockchain technology: scalability. But sharding is still a controversial topic. 

Why are some people so opposed to sharding, and how close are blockchains like Ethereum to implementing it?

What Is Database Sharding?

In a general sense, sharding refers to the process of breaking any type of database into smaller databases. The main benefit of sharding is that it allows data transactions to complete faster.

That is because when you spread your data across multiple databases, each database can process transactions at the same time as others. As a result, the more databases you have, the more transactions you can process concurrently. 

Sharding predates blockchain databases by many years. Sharding was a common practice among administrators of conventional databases well before the first blockchain, Bitcoin, appeared in 2009. 

What Is Blockchain Sharding?

That said, sharding has a somewhat narrower meaning within a blockchain-specific context. Blockchain sharding entails having different nodes on the blockchain process different transactions. In other words, instead of having each node record every transaction that takes place on the entire blockchain, some nodes would process certain transactions, while others process other transactions.

There would still be redundancy, meaning that multiple nodes would process the same transaction. But not all transactions would be processed by all nodes.

The Risks of Blockchain Sharding 

Since the idea of sharding first showed up on the radar of blockchain developers about three years ago, it has driven a lot of controversy. The controversy stems from the fact that, traditionally, having every node process every transaction was a core tenet of the consensus architectures that lay the foundation for blockchains. Since there is no centralized authority verifying blockchain transactions, the network as a whole decides which transactions are valid. When you stop having every node process every transaction, you theoretically raise the risk that invalid transactions could be recorded by a subset of malicious nodes and remain unchecked because the rest of the network does not handle those transactions.

Proponents of blockchain sharding argue that it is eminently possible to mitigate the risk of invalid transactions on a sharded blockchain by ensuring that each transaction is processed by a sufficient number of nodes. Still, due probably to the fact that sharding runs contrary to one of the founding principles of blockchain architecture, sharding is an idea that many folks have trouble swallowing.

From a technical perspective, calculating the security risks of blockchain sharding more precisely would depend on a variety of factors that are specific to the type of blockchain you want to share, as well as the sharding technique you use. Some blockchains can be sharded more easily — and perhaps more securely — than others; for example, because the Bitcoin blockchain lacks native support for smart contracts, it would likely be more difficult to implement a highly secure sharding architecture for Bitcoin than it would be on the Ethereum blockchain. There are also multiple ways to achieve sharding, each with different pros and cons. 

Blockchain Sharding Benefits

In addition to arguing that blockchain sharding can be performed securely, sharding advocates also contend that sharding is the best way to solve the rather serious problem of blockchain scalability.

Bitcoin has famously faced scalability limitations as its popularity has grown and the ability of the Bitcoin network to process transactions has rapidly declined. This led to SegWit, which improved Bitcoin’s scalability by increasing the block size. But even with larger block sizes, bitcoin transactions may become unacceptably slow again in the future as the level of network activity increases. Meanwhile, other blockchains face scalability issues of their own that could potentially be solved using sharding. 

Sharding offers promise for solving blockchain scalability issues permanently because the number of “shards” in the blockchain — that is, the number of nodes that process only certain transactions in order to improve overall transaction rates — could scale up without limit as the size of the blockchain itself increases. The more nodes you have on the network, the greater your ability to shard the network into smaller subsets of nodes that can share in the work of processing transactions, while at the same time having each subset of nodes remain large enough to ensure consensus. 

The State of Blockchain Sharding

Despite the potential benefits of blockchain sharding, attempts to implement the concept have so far been limited. Vitalik Buterin, one of the co-founders of the Ethereum blockchain, has proposed a sharding protocol. Buterin also declared on Twitter in late April 2018 that “sharding is coming,” although the source code that his tweet referenced appears not to have been updated since the time of the tweet. While Buterin’s public support for sharding means that the idea has high-profile endorsement in the Ethereum community, it remains unclear when an Ethereum sharding protocol might actually be implemented.

On other blockchains, support for sharding seems a remote possibility, at least for now. Discussion of a generic blockchain sharding protocol among Bitcoin developers in fall 2017 dropped off without any step toward concrete action. 

Perhaps the closest thing to blockchain sharding that is possible today is inter-blockchain communication via protocols such as Interledger. Interledger doesn’t shard a single blockchain; instead, it makes it easy to exchange data between different blockchains. A protocol like Interledger could conceivably be used to create processes that resemble sharding by spreading transactions across multiple blockchains, then using inter-blockchain communication to share data when needed. This approach could potentially deliver the same scalability benefits as sharding without requiring any blockchain to shard its own transactions.

For now, though, even this type of solution has yet to be implemented in the interest of achieving something that resembles sharding. While sharding is likely to continue to drive excited debate in blockchain communities, it does not appear likely that any major blockchain will announce support for sharding in the near future.

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