This piece of information got me confused

[estgari]

Hello!

I was reading some information regarding the validation of blocks and I found this piece of information while navigating through the Bitcoin Core web page, specifically the Blockchain Guide.

"Each full node in the Bitcoin network independently stores a block chain containing only blocks validated by that node".

Could anyone explain me how is that a full node does not store the entire Blockchain and just stores the Blocks validated by the node.
Here is the reference I found. https://bitcoin.org/en/developer-guide#block-chain

[pooya87]

Could anyone explain me how is that a full node does not store the entire Blockchain and just stores the Blocks validated by the node.

nodes are storing the entire blockchain. that is why they are full nodes.
what that statement means is two things. first that nodes validate blocks independently and second is that if an invalid block is given to a node, that node won't store it.
for example as a node you start syncing:
receive block #1 > validate > add to your local blockchain
receive block #2 > validate > add to your local blockchain
receive block #3 > validate > if it is invalid don't store, discard > look for block #3 > validate > add to local blockchain
receive block #4 > ...
continue until you reach last block and have the whole blockchain.

[bones261]

The blocks validated by the full node is the full blockchain according to that node. A full node could use modified software(ie Bitcoin Unlimited, UASF) and elect to tighten or relax certain rules for validation of a block to include in their version of the chain. However, if they cannot get other full nodes to also agree with their consensus changes(particularly a miner node that will build further blocks on their chain) they could find that their node is stranded on a frozen chain for tightened rules. (For relaxed rules, their chain will just end up being reorganized if the majority of miners won't build on top of the chain.)

[Foxpup]

It's explained in the very next sentence. "When several nodes all have the same blocks in their block chain, they are considered to be in consensus." Blocks that are not validated by nodes are not part of the consensus blockchain. Full nodes do store the entire blockchain, to the extent that it consists entirely of validated blocks, at the exclusion of all invalid blocks (which are not part of the blockchain and never will be, despite what some people seem to think).

[aliashraf]

Let's put it this way:

Each full node validates the blockchain up to the height that it has received and validated independently.
It is always possible to find two full nodes not being in full synchronization because of several reasons:
1- There might be temporary disagreements on the latest few blocks because of asymmetric topology of the network.
2-  Two nodes may use different versions or entirely different implementations and in special circumstances they split from each other.
3- A node may be down for a while and have a shorter chain validated.
...

All non-intentional forks are supposed to be resolved with or without user intervention eventually.