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loop/docs/faqs.md
Justin OBrien f295dc9c94 Address comments
Added faqs with fees explainer, regtest section from Oli's PR, and several other tweaks
2021-03-21 09:10:17 -10:00

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# Frequently Asked Questions
## How does Loop recover from a crash?
When `loopd` is terminated (or killed) for whatever reason, it will pickup
pending swaps after a restart.
Information about pending swaps is stored persistently in the swap database.
Its location is `~/.loopd/<network>/loop.db`.
## Can Loop handle multiple simultaneous swaps?
It is possible to execute multiple swaps simultaneously. Just keep loopd
running.
## What are the fees?
You can pass the `--verbose` flag when using Loop to get a detailed fee
breakdown
### Loop Out Fees
An explanation of each fee:
- **Estimated on-chain fee**: The estimated cost to sweep the
HTLC in case of success, calculated based on the _current_ on-chain fees.
This value is called `miner_fee` in the gRPC/REST responses.
- **Max on-chain fee**: The maximum on-chain fee the daemon
is going to allow for sweeping the HTLC in case of success. A fee estimation
based on the `--conf_target` flag is always performed before sweeping. The
factor of `100` times the estimated fee is applied in case the fees spike
between the time the swap is initiated and the time the HTLC can be swept. But
that is the absolute worst-case fee that will be paid. If there is no fee
spike, a normal, much lower fee will be used.
- **Max off-chain swap routing fee**: The maximum off-chain
routing fee that the daemon should pay when finding a route to pay the
Lightning invoice. This is a hard limit. If no route with a lower or equal fee
is found, the payment (and the swap) is aborted. This value is calculated
statically based on the swap amount (see `maxRoutingFeeBase` and
`maxRoutingFeeRate` in `cmd/loop/main.go`).
- **Max off-chain prepay routing fee**: The maximum off-chain routing
fee that the daemon should pay when finding a route to pay the prepay fee.
This is a hard limit. If no route with a lower or equal fee is found, the
payment (and the swap) is aborted. This value is calculated statically based
on the prepay amount (see `maxRoutingFeeBase` and `maxRoutingFeeRate` in
`cmd/loop/main.go`).
- **No show penalty (prepay)**: This is the amount that has to be
pre-paid (off-chain) before the server publishes the HTLC on-chain. This is
necessary to ensure the server's on-chain fees are paid if the client aborts
and never completes the swap _after_ the HTLC has been published on-chain.
If the swap completes normally, this amount is counted towards the full swap
amount and therefore is actually a pre-payment and not a fee. This value is
called `prepay_amt` in the gRPC/REST responses.
### Loop In Fees
An explanation of each fee:
- **Estimated on-chain fee**: The estimated on-chain fee that the
daemon has to pay to publish the HTLC. This is an estimation from `lnd`'s
wallet based on the available UTXOs and current network fees. This value is
called `miner_fee` in the gRPC/REST responses.