SHARDING

Some people will not classify sharding as a consensus mechanism because of how it works, but I consider it one because the protocol involves validating blocks and transactions like other consensus mechanisms. Sharding simply involves dividing a blockchain organization's entire network into a number of smaller networks. One shard stands out as distinct and independent of other shards because it contains data that is exclusive to it. For example, one shard could be tasked with validating blocks and transactions from Ethereum only.

HOW DOES SHARDING WORK
As I said earlier, some people do not consider sharding as a consensus mechanism and one of the reasons is that sharding usually works together with other consensus mechanisms as it doesn’t usually work alone. For instance, both Near protocol and Ethereum that have adopted sharding are Proof of Stake blockchains. So here, multiple blockchains are run instead of one whole blockchain, as it is divided into different blockchain bits called “shards, with each shard having its own set of validators that verify transactions, and produce blocks either by mining (Proof of Work) or by Staking or a Voting based mechanism (Proof of Stake). By doing this, the throughput of the blockchain is increased thereby ensuring faster and smoother transactions (Scalability). On some blockchains, these shards are able to communicate with each other in an interoperable manner, while on some they are isolated and independent.

As of now, both Near protocol and Ethereum are developing a sharding protocol for their blockchain but Near protocol is ahead as they have already launched the first Phase of the Sharding upgrade. They call it “Nightshade”.

PROS AND CONS OF SHARDING

PROS
Scalability.

It can foster interoperability as these shards will be able to communicate with one another as well as communicate with different chains outside their respective ecosystems.

With the help of sharded blockchains, nodes can avoid downloading the entire blockchain's history or having to validate each transaction that moves through the network. By doing this, the network's performance is enhanced, and blockchains can expand to support more users as well as keep the network protected from attackers.

CONS
Not all blockchains that adopt sharding will adopt its interoperable capability, therefore limiting the ability, reach, and interoperability of said network/chain.
Networks/chains that adopt sharding will as well carry the cons of the consensus mechanisms they are attached with.