This concept has been known since the end of the last century and got its name from the term "shard", that is, a fragment. And this term itself comes from Ultima Online - one of the first multiplayer online role-playing games, the developers of which coped with traffic by distributing players across various servers (game "worlds"). You know examples of sharding from business, for example, when customers are distributed into several groups according to geographical location, which are fixed on separate servers.
What are the features of shards in the blockchain? Each of them includes a unique set of smart contracts and account balances, and also has a node assigned to it that verifies all internal transactions and operations. That is, now the node is responsible for verifying transactions not in the entire network, but only inside a specific shard, which allows you to noticeably increase the number of processed operations. From this, the key purpose of sharding becomes obvious. It consists in dividing the blockchain into more manageable segments, thereby increasing the transaction throughput and solving the scalability problem, which is very acute for almost all modern blockchains.
It sounds encouraging, but is everything really rosy? As usual, there are some nuances. For example, the complication of communication and the reduction of network security. With communication, everything is logical - shards are isolated segments, which makes the interaction of users of different subdomains impossible without special mechanisms. As for security, the whole point here is that it is easier for hackers to capture a separate shard, and then, for example, send invalid transactions to the main network. However, Ethereum has already proposed a way to patch this gap, namely, randomized sampling. It assumes a random algorithm for assigning shard protocols to various sections to confirm the authentication of blocks.
So, which of the giants of the crypto market is already using sharding? The Zilliqa platform became a pioneer in this matter. But the Near blockchain ecosystem claims that its sharding technology provides such small node sizes that they can function even on low-performance devices - for example, this may soon become possible even on mobile phones. Ethereum, Cardano, QuarkChain and PChain did not stand aside either.
As you can see, sharding is another, and quite successful, attempt to finally solve the so-called blockchain trilemma. According to Vitalik Buterin, it consists in the fact that of the three key characteristics of the blockchain (security, decentralization and scalability), it is possible to save only two at the same time. Sharding is a kind of answer to this difficult challenge. According to experts, if its errors and shortcomings can be eliminated, the way will be opened to the effective scaling of the blockchain without threats and damage to its security and decentralization.