About disregarded blocks.. (out of main chain)

[aup1]

Hello, I'm new to this bitcoin system, so I've been reading some instructions which leads to a few questions.

1. let's assume two blocks are created at the same time which leads to two block chains(A,B).
In this case, I mean at the time when there are two block chains, I'm wondering what happens to the transactions(T) in both the last block of A and the last block of B.
It looks like T is going to be double verified?

2. continuing question no 1, let's say chain A becomes longer than chain B and becomes the main block chain.

In this case, I'm wondering what happens to the transactions only in the disregarded block (last block of block chain B). Are they disregarded like nothing happened? or something else?

Thanks.
 



 

[CIYAM]

Each mining node will build either on A or B (but never both) to extend the chain (so only one or other set of transactions is considered "confirmed" by each of the miners).

If a miner later sees that A or B was incorrect then they perform what is called a re-org which basically means that they undo everything (back the block before A/B) and then redo the transactions using the other block instead (so it doesn't work like any normal accounting ledger and why you need to wait for confirmations before being confident that a transaction should be considered "okay" assuming that you are accepting it for the purchase of goods, etc.).

[aup1]

Each mining node will build either on A or B (but never both) to extend the chain (so only one or other set of transactions is considered "confirmed" by each of the miners).

If a miner later sees that A or B was incorrect then they perform what is called a re-org which basically means that they undo everything (back the block before A/B) and then redo the transactions using the other block instead (so it doesn't work like any normal accounting ledger and why you need to wait for confirmations before being confident that a transaction should be considered "okay" assuming that you are accepting it for the purchase of goods, etc.).

So you mean all the transactions are not "finally" confirmed until one block chain becomes the main chain right?

Thanks.

[CIYAM]

So you mean all the transactions are not "finally" confirmed until one block chain becomes the main chain right?

Effectively yes (understand that "finally" is not an absolute thing but the chances of a re-org happening after X confirmations gets harder and harder so that generally once say 6 confirmations have occurred it is considered as pretty much impossible for the transaction to end up later being "undone" by a re-org).

[aup1]

So you mean all the transactions are not "finally" confirmed until one block chain becomes the main chain right?

Effectively yes (understand that "finally" is not an absolute thing but the chances of a re-org happening after X confirmations gets harder and harder so that generally once say 6 confirmations have occurred it is considered as pretty much impossible for the transaction to end up later being "undone" by a re-org).

Ah... I see there is a possibility of being wrong despite there exists the only main chain.

Thank you very much.

[watashi-kokoto]

one chain will lose, either A or B

[sumail1234]

Thank you very much.
เกมคาสิโน

[Bitsaurus]

I would presume that up to 5 degrees (blocks) of branching can occur from the main chain since 6 is required for full confirmation.