Double spend question

[horace0812]

Today I received payment from a faucet, waiting confirmation for ages,
it showed that double spend detected few hours later,
and after a while, the transation disappear in my wallet.

I an still new to BTC...
What is double spend? Is it usual to happen?

[ranochigo]

Today I received payment from a faucet, waiting confirmation for ages,
it showed that double spend detected few hours later,
and after a while, the transation disappear in my wallet.

I an still new to BTC...
What is double spend? Is it usual to happen?

Double spending occurs when two different transaction spend the same output. Bitcoin is designed to not let this happen, one of the transaction will get confirmation and the other will be considered invalid, thus getting rejected by the network. I can't explain why is there a double spend but perhaps the owner/system resent another transaction after seeing that it is forgotten by majority of network. It isn't that usual but it can happen, your best bet is to contact the faucet's owner now.

[horace0812]

Today I received payment from a faucet, waiting confirmation for ages,
it showed that double spend detected few hours later,
and after a while, the transation disappear in my wallet.

I an still new to BTC...
What is double spend? Is it usual to happen?

Double spending occurs when two different transaction spend the same output. Bitcoin is designed to not let this happen, one of the transaction will get confirmation and the other will be considered invalid, thus getting rejected by the network. I can't explain why is there a double spend but perhaps the owner/system resent another transaction after seeing that it is forgotten by majority of network. It isn't that usual but it can happen, your best bet is to contact the faucet's owner now.

I still struggling why double spend will happened...
normally when you do the transaction, the amount will be deducted from your balance,
can I say double spend means 'I pay 2BTC out but my balance only hv 1BTC there'?

[ranochigo]

Today I received payment from a faucet, waiting confirmation for ages,
it showed that double spend detected few hours later,
and after a while, the transation disappear in my wallet.

I an still new to BTC...
What is double spend? Is it usual to happen?

Double spending occurs when two different transaction spend the same output. Bitcoin is designed to not let this happen, one of the transaction will get confirmation and the other will be considered invalid, thus getting rejected by the network. I can't explain why is there a double spend but perhaps the owner/system resent another transaction after seeing that it is forgotten by majority of network. It isn't that usual but it can happen, your best bet is to contact the faucet's owner now.

I still struggling why double spend will happened...
normally when you do the transaction, the amount will be deducted from your balance,
can I say double spend means 'I pay 2BTC out but my balance only hv 1BTC there'?

Firstly, any peers would only accept whichever transaction which it sees first(On default clients which majority of network run on). Which means if it sees the other transaction spending the same output, it would refuse to relay it. Double spend can happen intentionally or accidentally. If the clients automatically deletes the transaction history after a while of it not being confirmed, you can still craft a transaction from the output from the transaction and broadcast it. Those nodes which the previous transaction has dropped from the mempool will relay it. Once either of the transaction confirms, all of the network will accept it as the valid one and the other as invalid.