How does a miner get to know that a transaction is verified by all the nodes

Question

I have read that every transaction is broadcasted to all the nodes in the block chain and is verified by each node.The verified transactions are then picked up or forwarded to miner node which forms a block. M question is how does the miner know that a particular transaction is verified by all the nodes and also how does one node know whether the transaction verified by it has been verified by other nodes?

Answer 1

Contrary to the popular belief, it is the job of the full nodes on the network to verify the transactions, and miners are a subset of that (i.e. miners are also full nodes).

Rather miners only exist to establish the ordering of transactions, within certain restrictions. Full nodes can verify transactions without them being a block and without mining a block because the process of mining does not alter the transaction.

A full nodes merely needs to know the transactions that a given transaction spends from in order to determine whether the transaction is valid. Miners must do the same thing so that they only include valid transactions in their blocks. What miners exist to do is to establish the ordering of transactions. They are not there to say that a transaction is valid. Rather what they do is, when given two transactions that conflict with each other, say which one is "first" and thus the one that everyone else should believe. Bitcoin uses a first come, first serve system, and miners are only here to say which transaction was first. The two conflicting transactions must be valid as transaction validity is a precondition for this conflict resolution.