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Deposit Cache Finalization & Fast WS Sync (#2915)

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## Summary

The deposit cache now has the ability to finalize deposits. This will cause it to drop unneeded deposit logs and hashes in the deposit Merkle tree that are no longer required to construct deposit proofs. The cache is finalized whenever the latest finalized checkpoint has a new `Eth1Data` with all deposits imported.

This has three benefits:

1. Improves the speed of constructing Merkle proofs for deposits as we can just replay deposits since the last finalized checkpoint instead of all historical deposits when re-constructing the Merkle tree.
2. Significantly faster weak subjectivity sync as the deposit cache can be transferred to the newly syncing node in compressed form. The Merkle tree that stores `N` finalized deposits requires a maximum of `log2(N)` hashes. The newly syncing node then only needs to download deposits since the last finalized checkpoint to have a full tree.
3. Future proofing in preparation for [EIP-4444](https://eips.ethereum.org/EIPS/eip-4444) as execution nodes will no longer be required to store logs permanently so we won't always have all historical logs available to us.

## More Details

Image to illustrate how the deposit contract merkle tree evolves and finalizes along with the resulting `DepositTreeSnapshot`
![image](https://user-images.githubusercontent.com/37123614/151465302-5fc56284-8a69-4998-b20e-45db3934ac70.png)

## Other Considerations

I've changed the structure of the `SszDepositCache` so once you load & save your database from this version of lighthouse, you will no longer be able to load it from older versions.

Co-authored-by: ethDreamer <37123614+ethDreamer@users.noreply.github.com>
This commit is contained in:
ethDreamer
2022-10-30 04:04:24 +00:00
parent 46fbf5b98b
commit e8604757a2
35 changed files with 2302 additions and 171 deletions
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185
consensus/merkle_proof/src/lib.rs
View File

@@ -19,6 +19,8 @@ lazy_static! {
/// indices are populated by non-zero leaves (perfect for the deposit contract tree).
#[derive(Debug, PartialEq)]
pub enum MerkleTree {
/// Finalized Node
Finalized(H256),
/// Leaf node with the hash of its content.
Leaf(H256),
/// Internal node with hash, left subtree and right subtree.
@@ -41,6 +43,24 @@ pub enum MerkleTreeError {
DepthTooSmall,
// Overflow occurred
ArithError,
// Can't finalize a zero node
ZeroNodeFinalized,
// Can't push to finalized node
FinalizedNodePushed,
// Invalid Snapshot
InvalidSnapshot(InvalidSnapshot),
// Can't proof a finalized node
ProofEncounteredFinalizedNode,
// This should never happen
PleaseNotifyTheDevs,
}
#[derive(Debug, PartialEq, Clone)]
pub enum InvalidSnapshot {
// Branch hashes are empty but deposits are not
EmptyBranchWithNonZeroDeposits(usize),
// End of tree reached but deposits != 1
EndOfTree,
}
impl MerkleTree {
@@ -97,9 +117,11 @@ impl MerkleTree {
let right: &mut MerkleTree = &mut *right;
match (&*left, &*right) {
// Tree is full
(Leaf(_), Leaf(_)) => return Err(MerkleTreeError::MerkleTreeFull),
(Leaf(_), Leaf(_)) | (Finalized(_), Leaf(_)) => {
return Err(MerkleTreeError::MerkleTreeFull)
}
// There is a right node so insert in right node
(Node(_, _, _), Node(_, _, _)) => {
(Node(_, _, _), Node(_, _, _)) | (Finalized(_), Node(_, _, _)) => {
right.push_leaf(elem, depth - 1)?;
}
// Both branches are zero, insert in left one
@@ -107,7 +129,7 @@ impl MerkleTree {
*left = MerkleTree::create(&[elem], depth - 1);
}
// Leaf on left branch and zero on right branch, insert on right side
(Leaf(_), Zero(_)) => {
(Leaf(_), Zero(_)) | (Finalized(_), Zero(_)) => {
*right = MerkleTree::create(&[elem], depth - 1);
}
// Try inserting on the left node -> if it fails because it is full, insert in right side.
@@ -129,6 +151,7 @@ impl MerkleTree {
right.hash().as_bytes(),
));
}
Finalized(_) => return Err(MerkleTreeError::FinalizedNodePushed),
}
Ok(())
@@ -137,6 +160,7 @@ impl MerkleTree {
/// Retrieve the root hash of this Merkle tree.
pub fn hash(&self) -> H256 {
match *self {
MerkleTree::Finalized(h) => h,
MerkleTree::Leaf(h) => h,
MerkleTree::Node(h, _, _) => h,
MerkleTree::Zero(depth) => H256::from_slice(&ZERO_HASHES[depth]),
@@ -146,7 +170,7 @@ impl MerkleTree {
/// Get a reference to the left and right subtrees if they exist.
pub fn left_and_right_branches(&self) -> Option<(&Self, &Self)> {
match *self {
MerkleTree::Leaf(_) | MerkleTree::Zero(0) => None,
MerkleTree::Finalized(_) | MerkleTree::Leaf(_) | MerkleTree::Zero(0) => None,
MerkleTree::Node(_, ref l, ref r) => Some((l, r)),
MerkleTree::Zero(depth) => Some((&ZERO_NODES[depth - 1], &ZERO_NODES[depth - 1])),
}
@@ -157,16 +181,125 @@ impl MerkleTree {
matches!(self, MerkleTree::Leaf(_))
}
/// Finalize deposits up to deposit with count = deposits_to_finalize
pub fn finalize_deposits(
&mut self,
deposits_to_finalize: usize,
level: usize,
) -> Result<(), MerkleTreeError> {
match self {
MerkleTree::Finalized(_) => Ok(()),
MerkleTree::Zero(_) => Err(MerkleTreeError::ZeroNodeFinalized),
MerkleTree::Leaf(hash) => {
if level != 0 {
// This shouldn't happen but this is a sanity check
return Err(MerkleTreeError::PleaseNotifyTheDevs);
}
*self = MerkleTree::Finalized(*hash);
Ok(())
}
MerkleTree::Node(hash, left, right) => {
if level == 0 {
// this shouldn't happen but we'll put it here for safety
return Err(MerkleTreeError::PleaseNotifyTheDevs);
}
let deposits = 0x1 << level;
if deposits <= deposits_to_finalize {
*self = MerkleTree::Finalized(*hash);
return Ok(());
}
left.finalize_deposits(deposits_to_finalize, level - 1)?;
if deposits_to_finalize > deposits / 2 {
let remaining = deposits_to_finalize - deposits / 2;
right.finalize_deposits(remaining, level - 1)?;
}
Ok(())
}
}
}
fn append_finalized_hashes(&self, result: &mut Vec<H256>) {
match self {
MerkleTree::Zero(_) | MerkleTree::Leaf(_) => {}
MerkleTree::Finalized(h) => result.push(*h),
MerkleTree::Node(_, left, right) => {
left.append_finalized_hashes(result);
right.append_finalized_hashes(result);
}
}
}
pub fn get_finalized_hashes(&self) -> Vec<H256> {
let mut result = vec![];
self.append_finalized_hashes(&mut result);
result
}
pub fn from_finalized_snapshot(
finalized_branch: &[H256],
deposit_count: usize,
level: usize,
) -> Result<Self, MerkleTreeError> {
if finalized_branch.is_empty() {
return if deposit_count == 0 {
Ok(MerkleTree::Zero(level))
} else {
Err(InvalidSnapshot::EmptyBranchWithNonZeroDeposits(deposit_count).into())
};
}
if deposit_count == (0x1 << level) {
return Ok(MerkleTree::Finalized(
*finalized_branch
.get(0)
.ok_or(MerkleTreeError::PleaseNotifyTheDevs)?,
));
}
if level == 0 {
return Err(InvalidSnapshot::EndOfTree.into());
}
let (left, right) = match deposit_count.checked_sub(0x1 << (level - 1)) {
// left tree is fully finalized
Some(right_deposits) => {
let (left_hash, right_branch) = finalized_branch
.split_first()
.ok_or(MerkleTreeError::PleaseNotifyTheDevs)?;
(
MerkleTree::Finalized(*left_hash),
MerkleTree::from_finalized_snapshot(right_branch, right_deposits, level - 1)?,
)
}
// left tree is not fully finalized -> right tree is zero
None => (
MerkleTree::from_finalized_snapshot(finalized_branch, deposit_count, level - 1)?,
MerkleTree::Zero(level - 1),
),
};
let hash = H256::from_slice(&hash32_concat(
left.hash().as_bytes(),
right.hash().as_bytes(),
));
Ok(MerkleTree::Node(hash, Box::new(left), Box::new(right)))
}
/// Return the leaf at `index` and a Merkle proof of its inclusion.
///
/// The Merkle proof is in "bottom-up" order, starting with a leaf node
/// and moving up the tree. Its length will be exactly equal to `depth`.
pub fn generate_proof(&self, index: usize, depth: usize) -> (H256, Vec<H256>) {
pub fn generate_proof(
&self,
index: usize,
depth: usize,
) -> Result<(H256, Vec<H256>), MerkleTreeError> {
let mut proof = vec![];
let mut current_node = self;
let mut current_depth = depth;
while current_depth > 0 {
let ith_bit = (index >> (current_depth - 1)) & 0x01;
if let &MerkleTree::Finalized(_) = current_node {
return Err(MerkleTreeError::ProofEncounteredFinalizedNode);
}
// Note: unwrap is safe because leaves are only ever constructed at depth == 0.
let (left, right) = current_node.left_and_right_branches().unwrap();
@@ -187,7 +320,33 @@ impl MerkleTree {
// Put proof in bottom-up order.
proof.reverse();
(current_node.hash(), proof)
Ok((current_node.hash(), proof))
}
/// useful for debugging
pub fn print_node(&self, mut space: u32) {
const SPACES: u32 = 10;
space += SPACES;
let (pair, text) = match self {
MerkleTree::Node(hash, left, right) => (Some((left, right)), format!("Node({})", hash)),
MerkleTree::Leaf(hash) => (None, format!("Leaf({})", hash)),
MerkleTree::Zero(depth) => (
None,
format!("Z[{}]({})", depth, H256::from_slice(&ZERO_HASHES[*depth])),
),
MerkleTree::Finalized(hash) => (None, format!("Finl({})", hash)),
};
if let Some((_, right)) = pair {
right.print_node(space);
}
println!();
for _i in SPACES..space {
print!(" ");
}
println!("{}", text);
if let Some((left, _)) = pair {
left.print_node(space);
}
}
}
@@ -235,6 +394,12 @@ impl From<ArithError> for MerkleTreeError {
}
}
impl From<InvalidSnapshot> for MerkleTreeError {
fn from(e: InvalidSnapshot) -> Self {
MerkleTreeError::InvalidSnapshot(e)
}
}
#[cfg(test)]
mod tests {
use super::*;
@@ -255,7 +420,9 @@ mod tests {
let merkle_root = merkle_tree.hash();
let proofs_ok = (0..leaves.len()).all(|i| {
let (leaf, branch) = merkle_tree.generate_proof(i, depth);
let (leaf, branch) = merkle_tree
.generate_proof(i, depth)
.expect("should generate proof");
leaf == leaves[i] && verify_merkle_proof(leaf, &branch, depth, i, merkle_root)
});
@@ -274,7 +441,9 @@ mod tests {
let proofs_ok = leaves_iter.enumerate().all(|(i, leaf)| {
assert_eq!(merkle_tree.push_leaf(leaf, depth), Ok(()));
let (stored_leaf, branch) = merkle_tree.generate_proof(i, depth);
let (stored_leaf, branch) = merkle_tree
.generate_proof(i, depth)
.expect("should generate proof");
stored_leaf == leaf && verify_merkle_proof(leaf, &branch, depth, i, merkle_tree.hash())
});