When a network can no longer handle the volume of transactions that are being submitted to it, congestion arises. There are several reasons that contribute to this phenomenon, including inherent network properties like block size and block duration as well as external aspects like market volatility.
It's important to look at how blocks are added to the blockchain before getting into the specifics.
When the quantity of transactions submitted to the blockchain network exceeds its ability to handle them, congestion results.
Several factors can cause blockchain networks to become crowded:
- Increase in demand
The number of unconfirmed transactions in the mempool may surpass the number of blocks that can be contained as more users submit transactions to the blockchain. This is especially important for blockchains because they have built-in restrictions on block size and block time.
Increased transaction volume might be caused by a spike in transaction activity or by unexpected price volatility.
- Modest block size
A block's maximum size is specified by the block size of each blockchain. A block's maximum number of transactions is constrained by this block size.
For instance, the maximum block size for Bitcoin at first was 1 megabyte. Segregated Witness, also known as SegWit, was added to Bitcoin in 2017 to increase transaction throughput. It raises the maximum theoretical block size to almost 4 MB.
The network becomes congested if the number of transactions goes over this threshold.
- lengthy block times
Block time is the frequency at which new blocks are added to the blockchain. A new block is added to Bitcoin every 10 minutes or so. There will be a backlog of transactions if they are being made at a much faster rate and in greater number.
https://academy.binance.com/en/articles/what-is-blockchain-network-congestion