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Let's asume I make a transaction with no fee and doesn't get confirmed after a while (let's say 10 days).
Could it be confirmed after that if for some reason some miner keeps a copy? I don't ask if is likely to happen but if it is posible.
Can a bitcoin transaction get confirmed unexpectedly?
Answers
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Absolutely. There are cases of transactions remaining unconfirmed for several days and then getting confirmed.
If the transaction was ever broadcast and is still valid, it can be included in a block by any miner who wishes to include it.
Ok, so if that happens what should be done? And I understand that once the transaction is broadcasted there is no expiration date. If that is correct then your answer is correct. – Josu Goñi – 2016-07-22T17:16:19.023
2Correct. It sounds like you want to invalidate the old transaction. You can do that by spending at least one of the SAME inputs in a new transaction (with a correct fee this time). After that new transaction has a few confirmations, the old transaction will have become invalid and will never be confirmed anymore, since it would double-spend. – Jannes – 2016-07-22T18:25:02.597
I believe we should be able to set an expire date to our transactions, specially having in mind that in the future transactions could become expensive. – Josu Goñi – 2016-07-22T22:52:22.593