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I am surprised that there are 220k unconfirmed transactions in the blockchain. And more transactions are getting queued in every minute. If 6 blocks are mined in every hour then in an hour only 12000 transactions will be confirmed. But it seems in every second 3-10 transactions are added. So in an hour, approximate 21600 new transactions will be created.

So what will happen to the unconfirmed transactions, if they lose that money or the transaction will be canceled?

See one transaction (Transaction Details) made by one of my friends but not confirmed. So he is thinking to way out from bitcoin. I am so sad that no one will accept this currency if this cannot be solved.

Update: Please consider that I am new to Bitcoin, I just want to know what will happen to the transactions if it is expired?. Also if there is an address change in the transaction then to which address the refund will go (if it happen)

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If 6 blocks are mined in every hour then in an hour only 12000 transactions will be confirmed. But it seems in every second 3-10 transactions are added. So in an hour, approximate 21600 new transactions will be created.

That sounds approximately correct. Space for blocks is a free market, with a limited amount of supply. By definition that means that not every issued transaction will find a place. This is expected.

Also note that there is no minimum cost or maximum demand for transactions. A transaction chooses its own fee, and anyone in the world could just try to issue large amounts of very cheap transactions if there was excess space in blocks - requiring the whole world to validate them.

I am surprised that there are 220k unconfirmed transactions in the blockchain. And more transactions are getting queued in every minute.

There are zero unconfirmed transactions in the blockchain. The blockchain contains by definition only confirmed transactions. I assume you're looking at some website that shows you their list of unconfirmed transactions. But there is no guaranteed consistency across nodes. In particular, most nodes on the network use a mempool of limited size, which evicts the lowest fee transactions if it grows too large. On top of that, every node can choose their own policies for what unconfirmed transactions to accept.

The point here is that these is not so much a "queue" of waiting transactions. There is a market of offered transactions, and miners will pick some from them, in some order.

So what will happen to the unconfirmed transactions, if they lose that money or the transaction will be canceled?

The transactions are not in the blockchain, which means there is no consistency across the network about them, by definition. They may confirm at some point, or not. But as long as they don't confirm, they didn't happen. There is nothing to cancel, or to refund. From the point of view of the network, the transaction just hasn't gone through.

The question is what your wallet software or service will let you do. It may permit you to treat the transaction as abandoned, and allow you to respend the same money. Look for RBF (BIP125) if you want some technical details, but in short, it's a procedure that permits wallets to replace an outstanding transaction with another one that pays a higher fee.

See one transaction (Transaction Details) made by one of my friends but not confirmed. So he is thinking to way out from bitcoin. I am so sad that no one will accept this currency if this cannot be solved.

Bitcoin is inherently not a very convenient payment mechanism. It doesn't offer instant payments, or customer protection, or guarantees you're sending to a legitimate business.

All of these things are being worked on as systems to build into or on top of Bitcoin, but there is a lot of missing technology.

Update: Please consider that I am new to Bitcoin, I just want to know what will happen to the transactions if it is expired?. Also if there is an address change in the transaction then to which address the refund will go (if it happen)

Expiration is just one policy that some nodes choose to determine which transactions to keep in their memory pool. It's not very related to this issue, as anyone on the network could just re-broadcast an older transaction, and it can get accepted again by nodes after it was expired before.

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See https://github.com/bitcoin/bitcoin/issues/3722

Quote:

One proposal bandied about on IRC is to expire any transaction from the memory pool, that does not confirm within X blocks. Proposed value for X is 2 days, 144*2.

This seems to be implemented now.

  • It seems there is a mempool reset in 72 hrs. But that's my second Question then what will happend to the transaction? Also consider if there is an address change. – Manu Prasad Dec 8 '17 at 16:36
  • This is correct, but irrelevant. See my answer. – Pieter Wuille Dec 8 '17 at 22:52
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Nothing happens to the transaction. Anyone can resubmit it if they want to.

So what will happen to the unconfirmed transactions, if they lose that money or the transaction will be canceled?

Neither of those things happen. If the transaction does not execute, it does not do anything. Everything stays just the way it was. But the transaction is not cancelled, it is still a valid transaction that a miner could include in a block if they wanted to.

To avoid being in limbo potentially forever, it usually makes sense to intentionally create a conflicting transaction, typically with a larger fee.

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