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Optimize decoy selection by batching the get_outputs call per input

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Luke Parker 2022-05-14 02:12:54 -04:00
parent bf4d83ba70
commit 3f02ab3037
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GPG key ID: F9F1386DB1E119B6
1 changed files with 44 additions and 34 deletions
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78
coins/monero/src/transaction/decoys.rs
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@ -24,52 +24,61 @@ lazy_static! {
static ref GAMMA: Gamma<f64> = Gamma::new(19.28, 1.0 / 1.61).unwrap();
}
async fn select_single<R: RngCore + CryptoRng>(
async fn select_n<R: RngCore + CryptoRng>(
rng: &mut R,
rpc: &Rpc,
height: usize,
distribution: &[u64],
high: u64,
per_second: f64,
used: &mut HashSet<u64>
) -> Result<(u64, [EdwardsPoint; 2]), RpcError> {
used: &mut HashSet<u64>,
count: usize
) -> Result<Vec<(u64, [EdwardsPoint; 2])>, RpcError> {
// Panic if not enough decoys are available
// TODO: Simply create a TX with less than the target amount
if (high - MATURITY) < u64::try_from(DECOYS).unwrap() {
panic!("Not enough decoys available");
}
let mut o;
let mut output = None;
// Use a gamma distribution
while {
let mut age = GAMMA.sample(rng).exp();
if age > TIP_APPLICATION {
age -= TIP_APPLICATION;
} else {
age = (rng.next_u64() % u64::try_from(RECENT_WINDOW * BLOCK_TIME).unwrap()) as f64;
}
let mut confirmed = Vec::with_capacity(count);
while confirmed.len() != count {
let remaining = count - confirmed.len();
let mut candidates = Vec::with_capacity(remaining);
while candidates.len() != remaining {
// Use a gamma distribution
let mut age = GAMMA.sample(rng).exp();
if age > TIP_APPLICATION {
age -= TIP_APPLICATION;
} else {
// f64 does not have try_from available, which is why these are written with `as`
age = (rng.next_u64() % u64::try_from(RECENT_WINDOW * BLOCK_TIME).unwrap()) as f64;
}
o = (age * per_second) as u64;
(o >= high) || {
o = high - 1 - o;
let i = distribution.partition_point(|s| *s < o);
let prev = if i == 0 { 0 } else { i - 1 };
let n = distribution[i] - distribution[prev];
o = distribution[prev] + (rng.next_u64() % n.max(1));
(n == 0) || used.contains(&o) || {
output = rpc.get_outputs(&[o], height).await?[0];
if output.is_none() {
used.insert(o);
let o = (age * per_second) as u64;
if o < high {
let i = distribution.partition_point(|s| *s < (high - 1 - o));
let prev = i.saturating_sub(1);
let n = distribution[i] - distribution[prev];
if n != 0 {
let o = distribution[prev] + (rng.next_u64() % n);
if !used.contains(&o) {
// It will either actually be used, or is unusable and this prevents trying it again
used.insert(o);
candidates.push(o);
}
}
output.is_none()
}
}
} {}
// Insert the selected output
used.insert(o);
Ok((o, output.unwrap()))
let outputs = rpc.get_outputs(&candidates, height).await?;
for i in 0 .. outputs.len() {
if let Some(output) = outputs[i] {
confirmed.push((candidates[i], output));
}
}
}
Ok(confirmed)
}
// Uses VarInt as this is solely used for key_offsets which is serialized by monero-rs
@ -130,12 +139,9 @@ pub(crate) async fn select<R: RngCore + CryptoRng>(
// TODO: If we're spending 2 outputs of a possible 11 outputs, this will still fail
used.remove(&o.0);
let mut decoys = Vec::with_capacity(DECOYS);
// Select the full amount of ring members in decoys, instead of just the actual decoys, in order
// to increase sample size
for _ in 0 .. DECOYS {
decoys.push(select_single(rng, rpc, height, &distribution, high, per_second, &mut used).await?);
}
let mut decoys = select_n(rng, rpc, height, &distribution, high, per_second, &mut used, DECOYS).await?;
decoys.sort_by(|a, b| a.0.cmp(&b.0));
// Add back this output
@ -162,8 +168,12 @@ pub(crate) async fn select<R: RngCore + CryptoRng>(
// it'd increase the amount of decoys required to create this transaction and some banned
// outputs may be the best options
used.remove(&decoys[m].0);
decoys[m] = select_single(rng, rpc, height, &distribution, high, per_second, &mut used).await?;
}
decoys.splice(
0 .. DECOYS / 2,
select_n(rng, rpc, height, &distribution, high, per_second, &mut used, DECOYS / 2).await?
);
decoys.sort_by(|a, b| a.0.cmp(&b.0));
}
}