garage/src/table/merkle.rs

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Rust
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use std::convert::TryInto;
use std::sync::Arc;
use std::time::Duration;
use futures::select;
use futures_util::future::*;
use log::{debug, warn};
use serde::{Deserialize, Serialize};
use sled::transaction::{
ConflictableTransactionError, ConflictableTransactionResult, TransactionalTree,
};
use tokio::sync::{watch, Notify};
use garage_util::background::BackgroundRunner;
use garage_util::data::*;
use garage_util::error::Error;
pub type MerklePartition = [u8; 2];
pub fn hash_of_merkle_partition(p: MerklePartition) -> Hash {
let mut partition_pos = [0u8; 32];
partition_pos[0..2].copy_from_slice(&p[..]);
partition_pos.into()
}
pub fn hash_of_merkle_partition_opt(p: Option<MerklePartition>) -> Hash {
p.map(hash_of_merkle_partition)
.unwrap_or([0xFFu8; 32].into())
}
// This modules partitions the data in 2**16 partitions, based on the top
// 16 bits (two bytes) of item's partition keys' hashes.
// It builds one Merkle tree for each of these 2**16 partitions.
pub struct MerkleUpdater {
table_name: String,
background: Arc<BackgroundRunner>,
// Content of the todo tree: items where
// - key = the key of an item in the main table, ie hash(partition_key)+sort_key
// - value = the hash of the full serialized item, if present,
// or an empty vec if item is absent (deleted)
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pub(crate) todo: sled::Tree,
pub(crate) todo_notify: Notify,
// Content of the merkle tree: items where
// - key = .bytes() for MerkleNodeKey
// - value = serialization of a MerkleNode, assumed to be MerkleNode::empty if not found
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pub(crate) merkle_tree: sled::Tree,
empty_node_hash: Hash,
}
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#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct MerkleNodeKey {
// partition: first 16 bits (two bytes) of the partition_key's hash
pub partition: MerklePartition,
// prefix: a prefix for the hash of full keys, i.e. hash(hash(partition_key)+sort_key)
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#[serde(with = "serde_bytes")]
pub prefix: Vec<u8>,
}
#[derive(PartialEq, Eq, Debug, Serialize, Deserialize)]
pub enum MerkleNode {
// The empty Merkle node
Empty,
// An intermediate Merkle tree node for a prefix
// Contains the hashes of the 256 possible next prefixes
Intermediate(Vec<(u8, Hash)>),
// A final node for an item
// Contains the full key of the item and the hash of the value
Leaf(Vec<u8>, Hash),
}
impl MerkleUpdater {
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pub(crate) fn launch(
table_name: String,
background: Arc<BackgroundRunner>,
todo: sled::Tree,
merkle_tree: sled::Tree,
) -> Arc<Self> {
let empty_node_hash = blake2sum(&rmp_to_vec_all_named(&MerkleNode::Empty).unwrap()[..]);
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let ret = Arc::new(Self {
table_name,
background,
todo,
todo_notify: Notify::new(),
merkle_tree,
empty_node_hash,
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});
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let ret2 = ret.clone();
ret.background.spawn_worker(
format!("Merkle tree updater for {}", ret.table_name),
|must_exit: watch::Receiver<bool>| ret2.updater_loop(must_exit),
);
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ret
}
async fn updater_loop(
self: Arc<Self>,
mut must_exit: watch::Receiver<bool>,
) {
while !*must_exit.borrow() {
if let Some(x) = self.todo.iter().next() {
match x {
Ok((key, valhash)) => {
if let Err(e) = self.update_item(&key[..], &valhash[..]) {
warn!(
"({}) Error while updating Merkle tree item: {}",
self.table_name, e
);
}
}
Err(e) => {
warn!(
"({}) Error while iterating on Merkle todo tree: {}",
self.table_name, e
);
tokio::time::delay_for(Duration::from_secs(10)).await;
}
}
} else {
select! {
_ = self.todo_notify.notified().fuse() => (),
_ = must_exit.recv().fuse() => (),
}
}
}
}
fn update_item(&self, k: &[u8], vhash_by: &[u8]) -> Result<(), Error> {
let khash = blake2sum(k);
let new_vhash = if vhash_by.len() == 0 {
None
} else {
Some(Hash::try_from(&vhash_by[..]).unwrap())
};
let key = MerkleNodeKey {
partition: k[0..2].try_into().unwrap(),
prefix: vec![],
};
self.merkle_tree
.transaction(|tx| self.update_item_rec(tx, k, khash, &key, new_vhash))?;
let deleted = self
.todo
.compare_and_swap::<_, _, Vec<u8>>(k, Some(vhash_by), None)?
.is_ok();
if !deleted {
debug!(
"({}) Item not deleted from Merkle todo because it changed: {:?}",
self.table_name, k
);
}
Ok(())
}
fn update_item_rec(
&self,
tx: &TransactionalTree,
k: &[u8],
khash: Hash,
key: &MerkleNodeKey,
new_vhash: Option<Hash>,
) -> ConflictableTransactionResult<Option<Hash>, Error> {
let i = key.prefix.len();
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// Read node at current position (defined by the prefix stored in key)
// Calculate an update to apply to this node
// This update is an Option<_>, so that it is None if the update is a no-op
// and we can thus skip recalculating and re-storing everything
let mutate = match self.read_node_txn(tx, &key)? {
MerkleNode::Empty => {
if let Some(vhv) = new_vhash {
Some(MerkleNode::Leaf(k.to_vec(), vhv))
} else {
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// Nothing to do, keep empty node
None
}
}
MerkleNode::Intermediate(mut children) => {
let key2 = key.next_key(khash);
if let Some(subhash) = self.update_item_rec(tx, k, khash, &key2, new_vhash)? {
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// Subtree changed, update this node as well
if subhash == self.empty_node_hash {
intermediate_rm_child(&mut children, key2.prefix[i]);
} else {
intermediate_set_child(&mut children, key2.prefix[i], subhash);
}
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if children.len() == 0 {
// should not happen
warn!(
"({}) Replacing intermediate node with empty node, should not happen.",
self.table_name
);
Some(MerkleNode::Empty)
} else if children.len() == 1 {
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// We now have a single node (case when the update deleted one of only two
// children). Move that single child to this level of the tree.
let key_sub = key.add_byte(children[0].0);
let subnode = self.read_node_txn(tx, &key_sub)?;
tx.remove(key_sub.encode())?;
Some(subnode)
} else {
Some(MerkleNode::Intermediate(children))
}
} else {
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// Subtree not changed, nothing to do
None
}
}
MerkleNode::Leaf(exlf_key, exlf_hash) => {
if exlf_key == k {
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// This leaf is for the same key that the one we are updating
match new_vhash {
Some(vhv) if vhv == exlf_hash => None,
Some(vhv) => Some(MerkleNode::Leaf(k.to_vec(), vhv)),
None => Some(MerkleNode::Empty),
}
} else {
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// This is an only leaf for another key
if let Some(vhv) = new_vhash {
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// Move that other key to a subnode, create another subnode for our
// insertion and replace current node by an intermediary node
let (pos1, h1) = {
let key2 = key.next_key(blake2sum(&exlf_key[..]));
let subhash = self.put_node_txn(
tx,
&key2,
&MerkleNode::Leaf(exlf_key, exlf_hash),
)?;
(key2.prefix[i], subhash)
};
let (pos2, h2) = {
let key2 = key.next_key(khash);
let subhash =
self.put_node_txn(tx, &key2, &MerkleNode::Leaf(k.to_vec(), vhv))?;
(key2.prefix[i], subhash)
};
let mut int = vec![];
intermediate_set_child(&mut int, pos1, h1);
intermediate_set_child(&mut int, pos2, h2);
Some(MerkleNode::Intermediate(int))
} else {
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// Nothing to do, we don't want to insert this value because it is None,
// and we don't want to change the other value because it's for something
// else
None
}
}
}
};
if let Some(new_node) = mutate {
let hash = self.put_node_txn(tx, &key, &new_node)?;
Ok(Some(hash))
} else {
Ok(None)
}
}
// Merkle tree node manipulation
fn read_node_txn(
&self,
tx: &TransactionalTree,
k: &MerkleNodeKey,
) -> ConflictableTransactionResult<MerkleNode, Error> {
let ent = tx.get(k.encode())?;
match ent {
None => Ok(MerkleNode::Empty),
Some(v) => Ok(rmp_serde::decode::from_read_ref::<_, MerkleNode>(&v[..])
.map_err(|e| ConflictableTransactionError::Abort(e.into()))?),
}
}
fn put_node_txn(
&self,
tx: &TransactionalTree,
k: &MerkleNodeKey,
v: &MerkleNode,
) -> ConflictableTransactionResult<Hash, Error> {
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trace!("Put Merkle node: {:?} => {:?}", k, v);
if *v == MerkleNode::Empty {
tx.remove(k.encode())?;
Ok(self.empty_node_hash)
} else {
let vby = rmp_to_vec_all_named(v)
.map_err(|e| ConflictableTransactionError::Abort(e.into()))?;
let rethash = blake2sum(&vby[..]);
tx.insert(k.encode(), vby)?;
Ok(rethash)
}
}
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// Access a node in the Merkle tree, used by the sync protocol
pub(crate) fn read_node(&self, k: &MerkleNodeKey) -> Result<MerkleNode, Error> {
let ent = self.merkle_tree.get(k.encode())?;
match ent {
None => Ok(MerkleNode::Empty),
Some(v) => Ok(rmp_serde::decode::from_read_ref::<_, MerkleNode>(&v[..])?),
}
}
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pub fn merkle_tree_len(&self) -> usize {
self.merkle_tree.len()
}
pub fn todo_len(&self) -> usize {
self.todo.len()
}
}
impl MerkleNodeKey {
fn encode(&self) -> Vec<u8> {
let mut ret = Vec::with_capacity(2 + self.prefix.len());
ret.extend(&self.partition[..]);
ret.extend(&self.prefix[..]);
ret
}
pub fn next_key(&self, h: Hash) -> Self {
assert!(&h.as_slice()[0..self.prefix.len()] == &self.prefix[..]);
let mut s2 = self.clone();
s2.prefix.push(h.as_slice()[self.prefix.len()]);
s2
}
pub fn add_byte(&self, b: u8) -> Self {
let mut s2 = self.clone();
s2.prefix.push(b);
s2
}
}
fn intermediate_set_child(ch: &mut Vec<(u8, Hash)>, pos: u8, v: Hash) {
for i in 0..ch.len() {
if ch[i].0 == pos {
ch[i].1 = v;
return;
} else if ch[i].0 > pos {
ch.insert(i, (pos, v));
return;
}
}
ch.insert(ch.len(), (pos, v));
}
fn intermediate_rm_child(ch: &mut Vec<(u8, Hash)>, pos: u8) {
for i in 0..ch.len() {
if ch[i].0 == pos {
ch.remove(i);
return;
}
}
}
#[test]
fn test_intermediate_aux() {
let mut v = vec![];
intermediate_set_child(&mut v, 12u8, [12u8; 32].into());
assert_eq!(v, vec![(12u8, [12u8; 32].into())]);
intermediate_set_child(&mut v, 42u8, [42u8; 32].into());
assert_eq!(
v,
vec![(12u8, [12u8; 32].into()), (42u8, [42u8; 32].into())]
);
intermediate_set_child(&mut v, 4u8, [4u8; 32].into());
assert_eq!(
v,
vec![
(4u8, [4u8; 32].into()),
(12u8, [12u8; 32].into()),
(42u8, [42u8; 32].into())
]
);
intermediate_set_child(&mut v, 12u8, [8u8; 32].into());
assert_eq!(
v,
vec![
(4u8, [4u8; 32].into()),
(12u8, [8u8; 32].into()),
(42u8, [42u8; 32].into())
]
);
intermediate_set_child(&mut v, 6u8, [6u8; 32].into());
assert_eq!(
v,
vec![
(4u8, [4u8; 32].into()),
(6u8, [6u8; 32].into()),
(12u8, [8u8; 32].into()),
(42u8, [42u8; 32].into())
]
);
intermediate_rm_child(&mut v, 42u8);
assert_eq!(
v,
vec![
(4u8, [4u8; 32].into()),
(6u8, [6u8; 32].into()),
(12u8, [8u8; 32].into())
]
);
intermediate_rm_child(&mut v, 11u8);
assert_eq!(
v,
vec![
(4u8, [4u8; 32].into()),
(6u8, [6u8; 32].into()),
(12u8, [8u8; 32].into())
]
);
intermediate_rm_child(&mut v, 6u8);
assert_eq!(v, vec![(4u8, [4u8; 32].into()), (12u8, [8u8; 32].into())]);
intermediate_set_child(&mut v, 6u8, [7u8; 32].into());
assert_eq!(
v,
vec![
(4u8, [4u8; 32].into()),
(6u8, [7u8; 32].into()),
(12u8, [8u8; 32].into())
]
);
}