Is it possible that a transaction lost ?

[maplelake]

What if some transaction is mined into "orphaned block" ？Some node will remove it from mempool because it is in block. But as it is "orphaned block", the transaction is invalidate.

is it possible transaction is lost in bitcoin network?

[ranochigo]

Transactions won't be invalidated. If the block gets orphaned, the node should put all of the transactions in the orphaned block into their mempool again.

[nc50lc]

What if some transaction is mined into "orphaned block" ？Some node will remove it from mempool because it is in block. But as it is "orphaned block", the transaction is invalidate.

As you said: "in a block", orphaned blocks wont be saved in the nodes' blockchain
so, any transaction that's in it that doesn't belong to the valid block won't be removed from their mempool.

is it possible transaction is lost in bitcoin network?

Based from the scenario above, no.
But for other circumstances like being dropped from (mostly) all of the node's mempool due to long no-confirmation, yes.

[~Money~]

What if some transaction is mined into "orphaned block" ？Some node will remove it from mempool because it is in block. But as it is "orphaned block", the transaction is invalidate.

is it possible transaction is lost in bitcoin network?

No, if a block is orphan in one node, it means it has been mined on another node sooner, or it was unacceptable by nodes.
but if there has been a personal transaction from a personal wallet which faced this problem, it can be re-broadcast again from wallet to network to get the confirmation

[Thirdspace]

... Some node will remove it from mempool because it is in block. But as it is "orphaned block", the transaction is invalidate.

as you said it, "some", that means some other nodes still have it in their mempool
and they will keep broadcasting it until eventually it is dropped once it reaches max relay time limit

is it possible transaction is lost in bitcoin network?

in my understanding, transaction lost isn't possible in bitcoin network (decentralised)
but transaction dropped from mempool is happening all the time for the reason nc50lc said
and when it's dropped, you can always re broadcast it again or create a new one with higher fee

[AltcoinBuilder]

What if some transaction is mined into "orphaned block" ？Some node will remove it from mempool because it is in block. But as it is "orphaned block", the transaction is invalidate.

is it possible transaction is lost in bitcoin network?

quick answer: no

[Dabs]

If a transaction was included in a block that gets orphaned, it's likely that the same transaction will get included in another blook soon. There is no guarantee, but the transaction should stay in the mempool for awhile, and in a few blocks will eventually get confirmed.

It might even be possible that two (or more) competing blocks have the same transaction and all but one of them gets orphaned, the transaction is already included in both blocks and confirms.

[d5000]

Don't forget there's no 100% guarantee the transaction will be included on other blocks, especially if transaction have low fees.

Exactly. It isn't totally impossible. I can imagine situations where an unlucky user will be able to "lose" a transaction this way, if it was sent with low fees, and then a long row of full blocks occur where the fee is lower than the minimum fee to be included.

It is however very hard to really lose BTC because of that issue, because there is always the option of rebroadcasting it, as others pointed out. Even if a seller of a (virtual) good is naive enough to accept an 1-conf transaction, sends the virtual good to the buyer, and the block including it becomes orphaned, then the sender wouldn't be able to scam the receiver as long as the receiver of the transaction is using a full-fledged Bitcoin client (even Electrum should be enough) - because if he simply rebroadcasts the transaction he received it will be eventually confirmed.

The only option for the scammer would be to doublespend the output with a larger fee, but it would need extreme luck for the scammer to exploit that (it's virtually only possible if you're a big miner).

[ABCbits]

It is however very hard to really lose BTC because of that issue, because there is always the option of rebroadcasting it, as others pointed out. Even if a seller of a (virtual) good is naive enough to accept an 1-conf transaction, sends the virtual good to the buyer, and the block including it becomes orphaned, then the sender wouldn't be able to scam the receiver as long as the receiver of the transaction is using a full-fledged Bitcoin client (even Electrum should be enough) - because if he simply rebroadcasts the transaction he received it will be eventually confirmed.

True, but it requires the receiver to rebroadcast the transaction. The potential problems are :
1. The seller isn't aware about orphan block (unless the seller regularly check his/her bitcoin wallet)
2. If the seller don't "save" the raw transaction, it's not easy to find the raw transaction in order to rebroadcast it.

[d5000]

True, but it requires the receiver to rebroadcast the transaction. The potential problems are :
1. The seller isn't aware about orphan block (unless the seller regularly check his/her bitcoin wallet)
2. If the seller don't "save" the raw transaction, it's not easy to find the raw transaction in order to rebroadcast it.

Yep, you're right here. I don't think it's a real threat for security because most service providers and virtual goods sellers should be intelligent enough to require at least 2 confirmations. But it would be nice if wallet developers could provide a feature for that issue - it should be easy to implement (automatic rebroadcasting of "lost" received transactions).

That doesn't solve the problem if the receiver goes offline inmediately after receiving the tx (and the first confirmation), or uses a block explorer or online wallet to control transactions he received (which may be fooled temporarily by the orphan block). But that would be already very risky behaviour for a merchant.