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.
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.
answered Jul 22 '16 at 17:02
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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 Jul 22 '16 at 17:16
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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 Jul 22 '16 at 18:25
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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 Jul 22 '16 at 22:52
