What can cause transaction getting dropped from mempool?

[Little Mouse]

Usually, when someone uses too low fee despite current fee rate is high, that tx gets dropped from mempool and needs to re-broadcast or increase the fee.
What can be other cause? I have seen this thread- https://bitcointalk.org/index.php?topic=5250467.0
An user was having an issue of transaction not getting confirmed. He sent some Verge coin with a fee of 0.70 XVG. I am sure fee is not the case here. The fee is 0.10 XVG according to their website. Also, not such a shitcoin chain will have a lot of tx that some tx will get dropped for lower fee.

Then what caused the problem while he paid enough fee, he had updated with the latest version wallet also.
Why his transaction was unconfirmed and was not available in verge explorer?

[Bttzed03]

I don't see any reason why verified transactions will be dropped from the mempool other than not meeting the minimum transaction fee.

I'm not familiar with verge and I don't think many forum members are either. The example you linked was more like an error from the OP by using an beta/oudated qt wallet which couldn't connect to the main chain.

[nc50lc]

I have read the thread and saw someone mentioned "abandon transaction" (post link),
He might have removed the transaction from his mempool so that he can create another one using the same inputs.
By doing so, he effectively double-spent his original low-fee transaction that caused it to be dropped - the new transaction have a different hash/TXID.
In Bitcoin, we have a double-spend protection like: most nodes' mempool will reject any transactions that re-used an input already used by any of the previous transactions it received;
except if there's an "RBF flag".

Or it wan't propagated in the first place for some reason (eg. non-standard),
it's just sitting in his own mempool that's why it didn't appeared in any blockexplorer.

Other ways to get a transaction dropped is to wait for the default transaction expiration of 14-days approx (for Bitcoin).
It it wasn't mined after 14-days starting from the time it was received by the node, the transaction will be dropped.

Take note that Altcoins have different network rules than Bitcoin.

[Upgrade00]

I did a thread on transaction fees here - https://bitcointalk.org/index.php?topic=5251213.0 and while researching on it, insufficient transaction fees was the only reason giving for why a transaction would be dropped from the mempool. If a transaction is already verified by nodes, and has enough fees to cover the current feerate then it's going to get picked up by miners eventually if one waits long enough.

The user in question, probably had an issue with the wallet version they were using and I can see from that thread that the transaction has been cancelled and the coins reversed.

[hatshepsut93]

You need to understand that there's no such thing as a single mempool, every node has it's own and they can easily modify the default behavior if they want to. When a transaction disappears from block explorer, it means that it was delete from mempool(s) to which the block explorer connects. Some other mempools might still keep this transaction, and it might even get confirmed at some point if it reaches miners.

It's impossible to tell what was the reason in that particular case, especially since it's a shitcoin - maybe miners didn't like such a low fee and didn't include it even though they had empty space in blocks, maybe it's some bug, maybe some nodes tried to censor that transaction by refusing to propagate it.

[Little Mouse]

He might have removed the transaction from his mempool so that he can create another one using the same inputs.

He removed the transaction after waiting couple of days. The tx was unconfirmed for couple of days on his old wallet version, later he updated the wallet but still it was unconfirmed. Then he managed to remove the tx.
Was it because of wallet version, he was in a wrong chain? If that was the case, I think in the updated wallet, the transaction would not be visible.
I got all the above point but still that does not fit the answer.

maybe miners didn't like such a low fee and didn't include it even though they had empty space in blocks,

According to the verge website FAQ, the fee is 0.10 XVG while the user used 0.70 XVG fee.

[nc50lc]

-snip-

-snip-
Was it because of wallet version, he was in a wrong chain? If that was the case, I think in the updated wallet, the transaction would not be visible.
I got all the above point but still that does not fit the answer.

So it looks like the second scenario in my post.
Since he had been using the old client, it might have created a "non-standard" transaction and that Tx was rejected by his peers,
He's the only one who can see the transaction (or users with old client), that's why it's not visible in blockexplorers.

After he updated the client and abandoned the Tx, he created a new "standard" transaction as written in his last post.

[ChuckBuck]

So it looks like the second scenario in my post.
Since he had been using the old client, it might have created a "non-standard" transaction and that Tx was rejected by his peers,
He's the only one who can see the transaction (or users with old client), that's why it's not visible in blockexplorers.

I understand what you explained, it's really good. But is he not the only one who can see the transaction? As soon as he uses the new client, his transaction is still there, he can manage to cancel it. The transaction is still there but not done, right? I mean people who can see transaction? Only him?
I would also like to ask, how do I cancel a BTC transaction if it's not done after 14 days?

[Little Mouse]

I understand what you explained, it's really good. But is he not the only one who can see the transaction? As soon as he uses the new client, his transaction is still there, he can manage to cancel it. The transaction is still there but not done, right? I mean people who can see transaction? Only him?

It will be seen on your client, not in explorer anymore since the tx may be not standard or rejected by mempool.

I would also like to ask, how do I cancel a BTC transaction if it's not done after 14 days?

I don't know if it's possible in other wallet, it can be done im Electrum wallet. In electrum, if you click the tx, there will be option to remove the tx.

[ChuckBuck]

It will be seen on your client, not in explorer anymore since the tx may be not standard or rejected by mempool.

But where is it stored? It is done on the old client, if it is not visible in the network, how does it display on the new client?

I don't know if it's possible in other wallet, it can be done im Electrum wallet. In electrum, if you click the tx, there will be option to remove the tx.

It has no option to cancel the transaction if the transaction is made within 14 days, right?

[alkuluku]

I don't know if it's possible in other wallet, it can be done im Electrum wallet. In electrum, if you click the tx, there will be option to remove the tx.

It has no option to cancel the transaction if the transaction is made within 14 days, right?

I dont think its in our hand to cancel a transaction at any point. Only if its dropped we get it back but soon it gets re-broadcast by itself.

[tsaroz]

You need to push the transaction with very low transaction fees to be dropped from mempool. People are doing their transactions as low as 4sat/byte so it's rare to be not being able to be picked by a node at the moment. Some wallet do pop cancel transaction until it's broadcasted to mempool. But after being broadcasted, there's no going back.

[Little Mouse]

But where is it stored? It is done on the old client, if it is not visible in the network, how does it display on the new client?

When you update to new client, you still have to use the previous wallet.dat file to restore your wallet which dtull have the same data of previous wallet.

It has no option to cancel the transaction if the transaction is made within 14 days, right?

I don't know if it's 14 days. If I can remember correctly, I was able to remove after 7/8 days or so. Usually, when it's get dropped from mempool (I have a little confusion now though.).

[ChuckBuck]

I dont think its in our hand to cancel a transaction at any point. Only if its dropped we get it back but soon it gets re-broadcast by itself.

I understand, basically, transactions on the Bitcoin network in particular and blockchain in general cannot be canceled or changed by anyone. I am talking about transactions that have dropped from the mempool.
What is the difference between this and double spend? Both occur when the transaction fee is set low  How to distinguish them?