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Bitcoin => Bitcoin Technical Support => Topic started by: Zyger on October 10, 2019, 05:34:55 AM



Title: What's the term for this scenario?
Post by: Zyger on October 10, 2019, 05:34:55 AM
Hey guys, I'm just wondering what the proper term for this scenario below is.

1) Person 1 sends some bitcoin to Person 2 with a deliberately small fee so it never gets confirmed.
2) The bitcoin eventually gets returned to Person 1 as the fee was too low.

I've seen some people on another forums calling it double spending, but I'm pretty sure that's not what it is.

Thanks!


Title: Re: What's the term for this scenario?
Post by: pooya87 on October 10, 2019, 05:48:28 AM
no, that is not double spending. it is just an unconfirmed transaction which has always been unsafe to accept (considered as payment being made for instance). also remember that when a transaction is made and broadcast to the network, technically it can remain out there forever. for instance the receiver can store it locally and keep broadcasting it until it either is confirmed or becomes invalid. so technically it could never "gets returned to person 1".

this transaction could be considered a "double spend" only if person 1 spends the same input of that transaction in another transaction sending the coins to another different destination. an act which would make one of the transactions invalid (depending on which tx nodes have in their mempool or if one becomes confirmed)


Title: Re: What's the term for this scenario?
Post by: nc50lc on October 10, 2019, 05:52:05 AM
People often call that scenario as "transaction dropped from the mempool";
AFAIK, there's no common term for that; call it "dropped transaction"?
Since technically, the unspent outputs was never moved, so we can't call it "returned transaction".

And Yes, that's not "double spending".
Double spending is when a user broadcast two or more transaction that spent the same UTXO(s) [in an attempt to cancel the other(s)].


Title: Re: What's the term for this scenario?
Post by: LoyceV on October 10, 2019, 06:15:13 AM
People often call that scenario as "transaction dropped from the mempool";
And that's why it's recommended not to accept payments without confirmation. Always wait for at least one confirmation. Especially for higher amounts it's better to wait for more than one confirmation before closing any deal.

There's also an easy solution if you've received a payment with low fee: use CPFP (https://bitcoin.org/en/glossary/cpfp). In short: you make a transaction from the unconfirmed amount to another address you own, with a fee high enough to pay for both transactions. Note that you can only do this if you received the transaction in your own wallet for which you own the private keys (so don't use an exchange for receiving funds from third parties).


Title: Re: What's the term for this scenario?
Post by: HCP on October 10, 2019, 10:44:29 PM
1) Person 1 sends some bitcoin to Person 2 with a deliberately small fee so it never gets confirmed.
2) The bitcoin eventually gets returned to Person 1 as the fee was too low.

I've seen some people on another forums calling it double spending, but I'm pretty sure that's not what it is.
no, that is not double spending. it is just an unconfirmed transaction which has always been unsafe to accept (considered as payment being made for instance). also remember that when a transaction is made and broadcast to the network, technically it can remain out there forever. for instance the receiver can store it locally and keep broadcasting it until it either is confirmed or becomes invalid. so technically it could never "gets returned to person 1".
In addition to simply rebroadcasting... the receiver could actually execute a CPFP (Child Pays For Parent) transaction that spends the UTXO from the unconfirmed transaction with a large fee to push the original transaction through.

As others have said, unless the sender attempts to also spend the coins in a second transaction, it isn't double spending, it's just a really bad scam attempt :P