(not well tested) use merkle tree for sync

8 files changed, 752 insertions, 961 deletions

diff --git a/src/table/data.rs b/src/table/data.rs
index fa89fc27..6217bf6d 100644
--- a/src/table/data.rs
+++ b/src/table/data.rs
@@ -1,16 +1,16 @@
 use std::sync::Arc;
 
 use log::warn;
-use sled::Transactional;
 use serde_bytes::ByteBuf;
+use sled::Transactional;
 
+use garage_util::background::BackgroundRunner;
 use garage_util::data::*;
 use garage_util::error::*;
-use garage_util::background::BackgroundRunner;
 
-use crate::schema::*;
-use crate::merkle::*;
 use crate::crdt::CRDT;
+use crate::merkle::*;
+use crate::schema::*;
 
 pub struct TableData<F: TableSchema> {
 	pub name: String,
@@ -20,7 +20,10 @@ pub struct TableData<F: TableSchema> {
 	pub(crate) merkle_updater: Arc<MerkleUpdater>,
 }
 
-impl<F> TableData<F> where F: TableSchema {
+impl<F> TableData<F>
+where
+	F: TableSchema,
+{
 	pub fn new(
 		name: String,
 		instance: F,
@@ -45,7 +48,7 @@ impl<F> TableData<F> where F: TableSchema {
 			merkle_tree_store,
 		);
 
-		Arc::new(Self{
+		Arc::new(Self {
 			name,
 			instance,
 			store,
diff --git a/src/table/lib.rs b/src/table/lib.rs
index bb249a56..18c29c35 100644
--- a/src/table/lib.rs
+++ b/src/table/lib.rs
@@ -7,11 +7,11 @@ pub mod crdt;
 pub mod schema;
 pub mod util;
 
+pub mod data;
 pub mod merkle;
 pub mod replication;
-pub mod data;
+pub mod sync;
 pub mod table;
-pub mod table_sync;
 
 pub use schema::*;
 pub use table::*;
diff --git a/src/table/merkle.rs b/src/table/merkle.rs
index ef197dc8..92c18e09 100644
--- a/src/table/merkle.rs
+++ b/src/table/merkle.rs
@@ -15,6 +15,19 @@ 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.
@@ -37,10 +50,10 @@ pub(crate) struct MerkleUpdater {
 	empty_node_hash: Hash,
 }
 
-#[derive(Clone)]
+#[derive(Clone, Serialize, Deserialize)]
 pub struct MerkleNodeKey {
 	// partition: first 16 bits (two bytes) of the partition_key's hash
-	pub partition: [u8; 2],
+	pub partition: MerklePartition,
 
 	// prefix: a prefix for the hash of full keys, i.e. hash(hash(partition_key)+sort_key)
 	pub prefix: Vec<u8>,
@@ -214,8 +227,11 @@ impl MerkleUpdater {
 						// 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))?;
+							let subhash = self.put_node_txn(
+								tx,
+								&key2,
+								&MerkleNode::Leaf(exlf_key, exlf_hash),
+							)?;
 							(key2.prefix[i], subhash)
 						};
 						let (pos2, h2) = {
@@ -280,14 +296,11 @@ impl MerkleUpdater {
 	}
 
 	// Access a node in the Merkle tree, used by the sync protocol
-	pub(crate) fn read_node(
-		&self,
-		k: &MerkleNodeKey,
-	) -> Result<MerkleNode, Error> {
+	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[..])?)
+			Some(v) => Ok(rmp_serde::decode::from_read_ref::<_, MerkleNode>(&v[..])?),
 		}
 	}
 }
@@ -339,31 +352,77 @@ fn intermediate_rm_child(ch: &mut Vec<(u8, Hash)>, pos: u8) {
 #[test]
 fn test_intermediate_aux() {
 	let mut v = vec![];
-	
+
 	intermediate_set_child(&mut v, 12u8, [12u8; 32].into());
-	assert!(v == vec![(12u8, [12u8; 32].into())]);
-	
+	assert_eq!(v, vec![(12u8, [12u8; 32].into())]);
+
 	intermediate_set_child(&mut v, 42u8, [42u8; 32].into());
-	assert!(v == vec![(12u8, [12u8; 32].into()), (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!(v == vec![(4u8, [4u8; 32].into()), (12u8, [12u8; 32].into()), (42u8, [42u8; 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!(v == vec![(4u8, [4u8; 32].into()), (12u8, [8u8; 32].into()), (42u8, [42u8; 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!(v == vec![(4u8, [4u8; 32].into()), (6u8, [6u8; 32].into()), (12u8, [8u8; 32].into()), (42u8, [42u8; 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!(v == vec![(4u8, [4u8; 32].into()), (6u8, [6u8; 32].into()), (12u8, [8u8; 32].into())]);
+	assert_eq!(
+		v,
+		vec![
+			(4u8, [4u8; 32].into()),
+			(6u8, [6u8; 32].into()),
+			(12u8, [8u8; 32].into())
+		]
+	);
 
 	intermediate_rm_child(&mut v, 11u8);
-	assert!(v == vec![(4u8, [4u8; 32].into()), (6u8, [6u8; 32].into()), (12u8, [8u8; 32].into())]);
+	assert_eq!(
+		v,
+		vec![
+			(4u8, [4u8; 32].into()),
+			(6u8, [6u8; 32].into()),
+			(12u8, [8u8; 32].into())
+		]
+	);
 
 	intermediate_rm_child(&mut v, 6u8);
-	assert!(v == vec![(4u8, [4u8; 32].into()), (12u8, [8u8; 32].into())]);
-	
+	assert_eq!(v, vec![(4u8, [4u8; 32].into()), (12u8, [8u8; 32].into())]);
+
 	intermediate_set_child(&mut v, 6u8, [7u8; 32].into());
-	assert!(v == vec![(4u8, [4u8; 32].into()), (6u8, [7u8; 32].into()), (12u8, [8u8; 32].into())]);
+	assert_eq!(
+		v,
+		vec![
+			(4u8, [4u8; 32].into()),
+			(6u8, [7u8; 32].into()),
+			(12u8, [8u8; 32].into())
+		]
+	);
 }
diff --git a/src/table/replication/fullcopy.rs b/src/table/replication/fullcopy.rs
index a62a6c3c..a20f20b7 100644
--- a/src/table/replication/fullcopy.rs
+++ b/src/table/replication/fullcopy.rs
@@ -53,7 +53,6 @@ impl TableReplication for TableFullReplication {
 	fn split_points(&self, _ring: &Ring) -> Vec<Hash> {
 		let mut ret = vec![];
 		ret.push([0u8; 32].into());
-		ret.push([0xFFu8; 32].into());
 		ret
 	}
 }
diff --git a/src/table/replication/sharded.rs b/src/table/replication/sharded.rs
index 42a742cd..886c7c08 100644
--- a/src/table/replication/sharded.rs
+++ b/src/table/replication/sharded.rs
@@ -44,11 +44,13 @@ impl TableReplication for TableShardedReplication {
 	fn split_points(&self, ring: &Ring) -> Vec<Hash> {
 		let mut ret = vec![];
 
-		ret.push([0u8; 32].into());
 		for entry in ring.ring.iter() {
 			ret.push(entry.location);
 		}
-		ret.push([0xFFu8; 32].into());
+		if ret.len() > 0 {
+			assert_eq!(ret[0], [0u8; 32].into());
+		}
+
 		ret
 	}
 }
diff --git a/src/table/sync.rs b/src/table/sync.rs
new file mode 100644
index 00000000..9c37c286
--- /dev/null
+++ b/src/table/sync.rs
@@ -0,0 +1,632 @@
+use std::collections::VecDeque;
+use std::convert::TryInto;
+use std::sync::{Arc, Mutex};
+use std::time::{Duration, Instant};
+
+use futures::future::join_all;
+use futures::{pin_mut, select};
+use futures_util::future::*;
+use futures_util::stream::*;
+use rand::Rng;
+use serde::{Deserialize, Serialize};
+use serde_bytes::ByteBuf;
+use tokio::sync::{mpsc, watch};
+
+use garage_rpc::ring::Ring;
+use garage_util::data::*;
+use garage_util::error::Error;
+
+use crate::data::*;
+use crate::merkle::*;
+use crate::replication::*;
+use crate::*;
+
+const TABLE_SYNC_RPC_TIMEOUT: Duration = Duration::from_secs(30);
+
+// Do anti-entropy every 10 minutes
+const ANTI_ENTROPY_INTERVAL: Duration = Duration::from_secs(10 * 60);
+
+pub struct TableSyncer<F: TableSchema, R: TableReplication> {
+	data: Arc<TableData<F>>,
+	aux: Arc<TableAux<F, R>>,
+
+	todo: Mutex<SyncTodo>,
+}
+
+type RootCk = Vec<(MerklePartition, Hash)>;
+
+#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
+pub struct PartitionRange {
+	begin: MerklePartition,
+	// if end is None, go all the way to partition 0xFFFF included
+	end: Option<MerklePartition>,
+}
+
+#[derive(Serialize, Deserialize)]
+pub(crate) enum SyncRPC {
+	RootCkHash(PartitionRange, Hash),
+	RootCkList(PartitionRange, RootCk),
+	CkNoDifference,
+	GetNode(MerkleNodeKey),
+	Node(MerkleNodeKey, MerkleNode),
+	Items(Vec<Arc<ByteBuf>>),
+}
+
+struct SyncTodo {
+	todo: Vec<TodoPartition>,
+}
+
+#[derive(Debug, Clone)]
+struct TodoPartition {
+	range: PartitionRange,
+
+	// Are we a node that stores this partition or not?
+	retain: bool,
+}
+
+impl<F, R> TableSyncer<F, R>
+where
+	F: TableSchema + 'static,
+	R: TableReplication + 'static,
+{
+	pub(crate) fn launch(data: Arc<TableData<F>>, aux: Arc<TableAux<F, R>>) -> Arc<Self> {
+		let todo = SyncTodo { todo: vec![] };
+
+		let syncer = Arc::new(Self {
+			data: data.clone(),
+			aux: aux.clone(),
+			todo: Mutex::new(todo),
+		});
+
+		let (busy_tx, busy_rx) = mpsc::unbounded_channel();
+
+		let s1 = syncer.clone();
+		aux.system.background.spawn_worker(
+			format!("table sync watcher for {}", data.name),
+			move |must_exit: watch::Receiver<bool>| s1.watcher_task(must_exit, busy_rx),
+		);
+
+		let s2 = syncer.clone();
+		aux.system.background.spawn_worker(
+			format!("table syncer for {}", data.name),
+			move |must_exit: watch::Receiver<bool>| s2.syncer_task(must_exit, busy_tx),
+		);
+
+		let s3 = syncer.clone();
+		tokio::spawn(async move {
+			tokio::time::delay_for(Duration::from_secs(20)).await;
+			s3.add_full_sync();
+		});
+
+		syncer
+	}
+
+	async fn watcher_task(
+		self: Arc<Self>,
+		mut must_exit: watch::Receiver<bool>,
+		mut busy_rx: mpsc::UnboundedReceiver<bool>,
+	) -> Result<(), Error> {
+		let mut ring_recv: watch::Receiver<Arc<Ring>> = self.aux.system.ring.clone();
+		let mut nothing_to_do_since = Some(Instant::now());
+
+		while !*must_exit.borrow() {
+			let s_ring_recv = ring_recv.recv().fuse();
+			let s_busy = busy_rx.recv().fuse();
+			let s_must_exit = must_exit.recv().fuse();
+			let s_timeout = tokio::time::delay_for(Duration::from_secs(1)).fuse();
+			pin_mut!(s_ring_recv, s_busy, s_must_exit, s_timeout);
+
+			select! {
+				new_ring_r = s_ring_recv => {
+					if new_ring_r.is_some() {
+						debug!("({}) Adding ring difference to syncer todo list", self.data.name);
+						self.add_full_sync();
+					}
+				}
+				busy_opt = s_busy => {
+					if let Some(busy) = busy_opt {
+						if busy {
+							nothing_to_do_since = None;
+						} else {
+							if nothing_to_do_since.is_none() {
+								nothing_to_do_since = Some(Instant::now());
+							}
+						}
+					}
+				}
+				must_exit_v = s_must_exit => {
+					if must_exit_v.unwrap_or(false) {
+						break;
+					}
+				}
+				_ = s_timeout => {
+					if nothing_to_do_since.map(|t| Instant::now() - t >= ANTI_ENTROPY_INTERVAL).unwrap_or(false) {
+						nothing_to_do_since = None;
+						debug!("({}) Adding full sync to syncer todo list", self.data.name);
+						self.add_full_sync();
+					}
+				}
+			}
+		}
+		Ok(())
+	}
+
+	pub fn add_full_sync(&self) {
+		self.todo
+			.lock()
+			.unwrap()
+			.add_full_sync(&self.data, &self.aux);
+	}
+
+	async fn syncer_task(
+		self: Arc<Self>,
+		mut must_exit: watch::Receiver<bool>,
+		busy_tx: mpsc::UnboundedSender<bool>,
+	) -> Result<(), Error> {
+		while !*must_exit.borrow() {
+			let task = self.todo.lock().unwrap().pop_task();
+			if let Some(partition) = task {
+				busy_tx.send(true)?;
+				let res = self
+					.clone()
+					.sync_partition(&partition, &mut must_exit)
+					.await;
+				if let Err(e) = res {
+					warn!(
+						"({}) Error while syncing {:?}: {}",
+						self.data.name, partition, e
+					);
+				}
+			} else {
+				busy_tx.send(false)?;
+				tokio::time::delay_for(Duration::from_secs(1)).await;
+			}
+		}
+		Ok(())
+	}
+
+	async fn sync_partition(
+		self: Arc<Self>,
+		partition: &TodoPartition,
+		must_exit: &mut watch::Receiver<bool>,
+	) -> Result<(), Error> {
+		if partition.retain {
+			let my_id = self.aux.system.id;
+
+			let nodes = self
+				.aux
+				.replication
+				.write_nodes(
+					&hash_of_merkle_partition(partition.range.begin),
+					&self.aux.system,
+				)
+				.into_iter()
+				.filter(|node| *node != my_id)
+				.collect::<Vec<_>>();
+
+			debug!(
+				"({}) Syncing {:?} with {:?}...",
+				self.data.name, partition, nodes
+			);
+			let mut sync_futures = nodes
+				.iter()
+				.map(|node| {
+					self.clone()
+						.do_sync_with(partition.clone(), *node, must_exit.clone())
+				})
+				.collect::<FuturesUnordered<_>>();
+
+			let mut n_errors = 0;
+			while let Some(r) = sync_futures.next().await {
+				if let Err(e) = r {
+					n_errors += 1;
+					warn!("({}) Sync error: {}", self.data.name, e);
+				}
+			}
+			if n_errors > self.aux.replication.max_write_errors() {
+				return Err(Error::Message(format!(
+					"Sync failed with too many nodes (should have been: {:?}).",
+					nodes
+				)));
+			}
+		} else {
+			self.offload_partition(
+				&hash_of_merkle_partition(partition.range.begin),
+				&hash_of_merkle_partition_opt(partition.range.end),
+				must_exit,
+			)
+			.await?;
+		}
+
+		Ok(())
+	}
+
+	// Offload partition: this partition is not something we are storing,
+	// so send it out to all other nodes that store it and delete items locally.
+	// We don't bother checking if the remote nodes already have the items,
+	// we just batch-send everything. Offloading isn't supposed to happen very often.
+	// If any of the nodes that are supposed to store the items is unable to
+	// save them, we interrupt the process.
+	async fn offload_partition(
+		self: &Arc<Self>,
+		begin: &Hash,
+		end: &Hash,
+		must_exit: &mut watch::Receiver<bool>,
+	) -> Result<(), Error> {
+		let mut counter: usize = 0;
+
+		while !*must_exit.borrow() {
+			let mut items = Vec::new();
+
+			for item in self.data.store.range(begin.to_vec()..end.to_vec()) {
+				let (key, value) = item?;
+				items.push((key.to_vec(), Arc::new(ByteBuf::from(value.as_ref()))));
+
+				if items.len() >= 1024 {
+					break;
+				}
+			}
+
+			if items.len() > 0 {
+				let nodes = self
+					.aux
+					.replication
+					.write_nodes(&begin, &self.aux.system)
+					.into_iter()
+					.collect::<Vec<_>>();
+				if nodes.contains(&self.aux.system.id) {
+					warn!("Interrupting offload as partitions seem to have changed");
+					break;
+				}
+
+				counter += 1;
+				debug!(
+					"Offloading {} items from {:?}..{:?} ({})",
+					items.len(),
+					begin,
+					end,
+					counter
+				);
+				self.offload_items(&items, &nodes[..]).await?;
+			} else {
+				break;
+			}
+		}
+
+		Ok(())
+	}
+
+	async fn offload_items(
+		self: &Arc<Self>,
+		items: &Vec<(Vec<u8>, Arc<ByteBuf>)>,
+		nodes: &[UUID],
+	) -> Result<(), Error> {
+		let values = items.iter().map(|(_k, v)| v.clone()).collect::<Vec<_>>();
+		let update_msg = Arc::new(TableRPC::<F>::Update(values));
+
+		for res in join_all(nodes.iter().map(|to| {
+			self.aux
+				.rpc_client
+				.call_arc(*to, update_msg.clone(), TABLE_SYNC_RPC_TIMEOUT)
+		}))
+		.await
+		{
+			res?;
+		}
+
+		// All remote nodes have written those items, now we can delete them locally
+		let mut not_removed = 0;
+		for (k, v) in items.iter() {
+			if !self.data.delete_if_equal(&k[..], &v[..])? {
+				not_removed += 1;
+			}
+		}
+
+		if not_removed > 0 {
+			debug!("{} items not removed during offload because they changed in between (trying again...)", not_removed);
+		}
+
+		Ok(())
+	}
+
+	// ======= SYNCHRONIZATION PROCEDURE -- DRIVER SIDE ======
+
+	fn get_root_ck(&self, range: PartitionRange) -> Result<RootCk, Error> {
+		let begin = u16::from_be_bytes(range.begin);
+		let range_iter = match range.end {
+			Some(end) => {
+				let end = u16::from_be_bytes(end);
+				begin..=(end - 1)
+			}
+			None => begin..=0xFFFF,
+		};
+
+		let mut ret = vec![];
+		for i in range_iter {
+			let key = MerkleNodeKey {
+				partition: u16::to_be_bytes(i),
+				prefix: vec![],
+			};
+			match self.data.merkle_updater.read_node(&key)? {
+				MerkleNode::Empty => (),
+				x => {
+					ret.push((key.partition, hash_of(&x)?));
+				}
+			}
+		}
+		Ok(ret)
+	}
+
+	async fn do_sync_with(
+		self: Arc<Self>,
+		partition: TodoPartition,
+		who: UUID,
+		must_exit: watch::Receiver<bool>,
+	) -> Result<(), Error> {
+		let root_ck = self.get_root_ck(partition.range)?;
+		let root_ck_hash = hash_of(&root_ck)?;
+
+		// If their root checksum has level > than us, use that as a reference
+		let root_resp = self
+			.aux
+			.rpc_client
+			.call(
+				who,
+				TableRPC::<F>::SyncRPC(SyncRPC::RootCkHash(partition.range, root_ck_hash)),
+				TABLE_SYNC_RPC_TIMEOUT,
+			)
+			.await?;
+
+		let mut todo = match root_resp {
+			TableRPC::<F>::SyncRPC(SyncRPC::CkNoDifference) => {
+				debug!(
+					"({}) Sync {:?} with {:?}: no difference",
+					self.data.name, partition, who
+				);
+				return Ok(());
+			}
+			TableRPC::<F>::SyncRPC(SyncRPC::RootCkList(_, their_root_ck)) => {
+				let join = join_ordered(&root_ck[..], &their_root_ck[..]);
+				let mut todo = VecDeque::new();
+				for (p, v1, v2) in join.iter() {
+					let diff = match (v1, v2) {
+						(Some(_), None) | (None, Some(_)) => true,
+						(Some(a), Some(b)) => a != b,
+						_ => false,
+					};
+					if diff {
+						todo.push_back(MerkleNodeKey {
+							partition: **p,
+							prefix: vec![],
+						});
+					}
+				}
+				debug!(
+					"({}) Sync {:?} with {:?}: todo.len() = {}",
+					self.data.name,
+					partition,
+					who,
+					todo.len()
+				);
+				todo
+			}
+			x => {
+				return Err(Error::Message(format!(
+					"Invalid respone to RootCkHash RPC: {}",
+					debug_serialize(x)
+				)));
+			}
+		};
+
+		let mut todo_items = vec![];
+
+		while !todo.is_empty() && !*must_exit.borrow() {
+			let key = todo.pop_front().unwrap();
+			let node = self.data.merkle_updater.read_node(&key)?;
+
+			match node {
+				MerkleNode::Empty => {
+					// They have items we don't have.
+					// We don't request those items from them, they will send them.
+					// We only bother with pushing items that differ
+				}
+				MerkleNode::Leaf(ik, _) => {
+					// Just send that item directly
+					if let Some(val) = self.data.store.get(ik)? {
+						todo_items.push(val.to_vec());
+					}
+				}
+				MerkleNode::Intermediate(l) => {
+					let remote_node = match self
+						.aux
+						.rpc_client
+						.call(
+							who,
+							TableRPC::<F>::SyncRPC(SyncRPC::GetNode(key.clone())),
+							TABLE_SYNC_RPC_TIMEOUT,
+						)
+						.await?
+					{
+						TableRPC::<F>::SyncRPC(SyncRPC::Node(_, node)) => node,
+						x => {
+							return Err(Error::Message(format!(
+								"Invalid respone to GetNode RPC: {}",
+								debug_serialize(x)
+							)));
+						}
+					};
+					let int_l2 = match remote_node {
+						MerkleNode::Intermediate(l2) => l2,
+						_ => vec![],
+					};
+
+					let join = join_ordered(&l[..], &int_l2[..]);
+					for (p, v1, v2) in join.into_iter() {
+						let diff = match (v1, v2) {
+							(Some(_), None) | (None, Some(_)) => true,
+							(Some(a), Some(b)) => a != b,
+							_ => false,
+						};
+						if diff {
+							todo.push_back(key.add_byte(*p));
+						}
+					}
+				}
+			}
+
+			if todo_items.len() >= 256 {
+				self.send_items(who, std::mem::replace(&mut todo_items, vec![]))
+					.await?;
+			}
+		}
+
+		if !todo_items.is_empty() {
+			self.send_items(who, todo_items).await?;
+		}
+
+		Ok(())
+	}
+
+	async fn send_items(&self, who: UUID, item_list: Vec<Vec<u8>>) -> Result<(), Error> {
+		info!(
+			"({}) Sending {} items to {:?}",
+			self.data.name,
+			item_list.len(),
+			who
+		);
+
+		let mut values = vec![];
+		for item in item_list.iter() {
+			if let Some(v) = self.data.store.get(&item[..])? {
+				values.push(Arc::new(ByteBuf::from(v.as_ref())));
+			}
+		}
+		let rpc_resp = self
+			.aux
+			.rpc_client
+			.call(who, TableRPC::<F>::Update(values), TABLE_SYNC_RPC_TIMEOUT)
+			.await?;
+		if let TableRPC::<F>::Ok = rpc_resp {
+			Ok(())
+		} else {
+			Err(Error::Message(format!(
+				"Unexpected response to RPC Update: {}",
+				debug_serialize(&rpc_resp)
+			)))
+		}
+	}
+
+	// ======= SYNCHRONIZATION PROCEDURE -- RECEIVER SIDE ======
+
+	pub(crate) async fn handle_rpc(self: &Arc<Self>, message: &SyncRPC) -> Result<SyncRPC, Error> {
+		match message {
+			SyncRPC::RootCkHash(range, h) => {
+				let root_ck = self.get_root_ck(*range)?;
+				let hash = hash_of(&root_ck)?;
+				if hash == *h {
+					Ok(SyncRPC::CkNoDifference)
+				} else {
+					Ok(SyncRPC::RootCkList(*range, root_ck))
+				}
+			}
+			SyncRPC::GetNode(k) => {
+				let node = self.data.merkle_updater.read_node(&k)?;
+				Ok(SyncRPC::Node(k.clone(), node))
+			}
+			_ => Err(Error::Message(format!("Unexpected sync RPC"))),
+		}
+	}
+}
+
+impl SyncTodo {
+	fn add_full_sync<F: TableSchema, R: TableReplication>(
+		&mut self,
+		data: &TableData<F>,
+		aux: &TableAux<F, R>,
+	) {
+		let my_id = aux.system.id;
+
+		self.todo.clear();
+
+		let ring = aux.system.ring.borrow().clone();
+		let split_points = aux.replication.split_points(&ring);
+
+		for i in 0..split_points.len() {
+			let begin: MerklePartition = {
+				let b = split_points[i];
+				assert_eq!(b.as_slice()[2..], [0u8; 30][..]);
+				b.as_slice()[..2].try_into().unwrap()
+			};
+
+			let end: Option<MerklePartition> = if i + 1 < split_points.len() {
+				let e = split_points[i + 1];
+				assert_eq!(e.as_slice()[2..], [0u8; 30][..]);
+				Some(e.as_slice()[..2].try_into().unwrap())
+			} else {
+				None
+			};
+
+			let begin_hash = hash_of_merkle_partition(begin);
+			let end_hash = hash_of_merkle_partition_opt(end);
+
+			let nodes = aux.replication.replication_nodes(&begin_hash, &ring);
+
+			let retain = nodes.contains(&my_id);
+			if !retain {
+				// Check if we have some data to send, otherwise skip
+				if data.store.range(begin_hash..end_hash).next().is_none() {
+					continue;
+				}
+			}
+
+			self.todo.push(TodoPartition {
+				range: PartitionRange { begin, end },
+				retain,
+			});
+		}
+	}
+
+	fn pop_task(&mut self) -> Option<TodoPartition> {
+		if self.todo.is_empty() {
+			return None;
+		}
+
+		let i = rand::thread_rng().gen_range::<usize, _, _>(0, self.todo.len());
+		if i == self.todo.len() - 1 {
+			self.todo.pop()
+		} else {
+			let replacement = self.todo.pop().unwrap();
+			let ret = std::mem::replace(&mut self.todo[i], replacement);
+			Some(ret)
+		}
+	}
+}
+
+fn hash_of<T: Serialize>(x: &T) -> Result<Hash, Error> {
+	Ok(blake2sum(&rmp_to_vec_all_named(x)?[..]))
+}
+
+fn join_ordered<'a, K: Ord + Eq, V1, V2>(
+	x: &'a [(K, V1)],
+	y: &'a [(K, V2)],
+) -> Vec<(&'a K, Option<&'a V1>, Option<&'a V2>)> {
+	let mut ret = vec![];
+	let mut i = 0;
+	let mut j = 0;
+	while i < x.len() || j < y.len() {
+		if i < x.len() && j < y.len() && x[i].0 == y[j].0 {
+			ret.push((&x[i].0, Some(&x[i].1), Some(&y[j].1)));
+			i += 1;
+			j += 1;
+		} else if i < x.len() && (j == y.len() || x[i].0 < y[j].0) {
+			ret.push((&x[i].0, Some(&x[i].1), None));
+			i += 1;
+		} else if j < y.len() && (i == x.len() || x[i].0 > y[j].0) {
+			ret.push((&x[i].0, None, Some(&y[j].1)));
+			j += 1;
+		} else {
+			unreachable!();
+		}
+	}
+	ret
+}
diff --git a/src/table/table.rs b/src/table/table.rs
index a4cb4b24..516c9358 100644
--- a/src/table/table.rs
+++ b/src/table/table.rs
@@ -15,9 +15,9 @@ use garage_rpc::rpc_server::*;
 
 use crate::crdt::CRDT;
 use crate::data::*;
-use crate::schema::*;
-use crate::table_sync::*;
 use crate::replication::*;
+use crate::schema::*;
+use crate::sync::*;
 
 const TABLE_RPC_TIMEOUT: Duration = Duration::from_secs(10);
 
@@ -50,7 +50,6 @@ pub(crate) enum TableRPC<F: TableSchema> {
 
 impl<F: TableSchema> RpcMessage for TableRPC<F> {}
 
-
 impl<F, R> Table<F, R>
 where
 	F: TableSchema + 'static,
@@ -69,29 +68,17 @@ where
 		let rpc_path = format!("table_{}", name);
 		let rpc_client = system.rpc_client::<TableRPC<F>>(&rpc_path);
 
-		let data = TableData::new(
-			name,
-			instance,
-			db,
-			system.background.clone(),
-		);
+		let data = TableData::new(name, instance, db, system.background.clone());
 
-		let aux = Arc::new(TableAux{
+		let aux = Arc::new(TableAux {
 			system,
 			replication,
 			rpc_client,
 		});
 
-		let syncer = TableSyncer::launch(
-			data.clone(),
-			aux.clone(),
-		);
+		let syncer = TableSyncer::launch(data.clone(), aux.clone());
 
-		let table = Arc::new(Self {
-			data,
-			aux,
-			syncer,
-		});
+		let table = Arc::new(Self { data, aux, syncer });
 
 		table.clone().register_handler(rpc_server, rpc_path);
 
@@ -106,7 +93,8 @@ where
 		let e_enc = Arc::new(ByteBuf::from(rmp_to_vec_all_named(e)?));
 		let rpc = TableRPC::<F>::Update(vec![e_enc]);
 
-		self.aux.rpc_client
+		self.aux
+			.rpc_client
 			.try_call_many(
 				&who[..],
 				rpc,
@@ -135,7 +123,11 @@ where
 		let call_futures = call_list.drain().map(|(node, entries)| async move {
 			let rpc = TableRPC::<F>::Update(entries);
 
-			let resp = self.aux.rpc_client.call(node, rpc, TABLE_RPC_TIMEOUT).await?;
+			let resp = self
+				.aux
+				.rpc_client
+				.call(node, rpc, TABLE_RPC_TIMEOUT)
+				.await?;
 			Ok::<_, Error>((node, resp))
 		});
 		let mut resps = call_futures.collect::<FuturesUnordered<_>>();
@@ -200,7 +192,8 @@ where
 			if not_all_same {
 				let self2 = self.clone();
 				let ent2 = ret_entry.clone();
-				self.aux.system
+				self.aux
+					.system
 					.background
 					.spawn_cancellable(async move { self2.repair_on_read(&who[..], ent2).await });
 			}
@@ -221,7 +214,8 @@ where
 		let rpc = TableRPC::<F>::ReadRange(partition_key.clone(), begin_sort_key, filter, limit);
 
 		let resps = self
-			.aux.rpc_client
+			.aux
+			.rpc_client
 			.try_call_many(
 				&who[..],
 				rpc,
@@ -276,7 +270,8 @@ where
 
 	async fn repair_on_read(&self, who: &[UUID], what: F::E) -> Result<(), Error> {
 		let what_enc = Arc::new(ByteBuf::from(rmp_to_vec_all_named(&what)?));
-		self.aux.rpc_client
+		self.aux
+			.rpc_client
 			.try_call_many(
 				&who[..],
 				TableRPC::<F>::Update(vec![what_enc]),
@@ -296,7 +291,8 @@ where
 		});
 
 		let self2 = self.clone();
-		self.aux.rpc_client
+		self.aux
+			.rpc_client
 			.set_local_handler(self.aux.system.id, move |msg| {
 				let self2 = self2.clone();
 				async move { self2.handle(&msg).await }
@@ -318,9 +314,7 @@ where
 				Ok(TableRPC::Ok)
 			}
 			TableRPC::SyncRPC(rpc) => {
-				let response = self.syncer
-					.handle_rpc(rpc, self.aux.system.background.stop_signal.clone())
-					.await?;
+				let response = self.syncer.handle_rpc(rpc).await?;
 				Ok(TableRPC::SyncRPC(response))
 			}
 			_ => Err(Error::BadRPC(format!("Unexpected table RPC"))),
diff --git a/src/table/table_sync.rs b/src/table/table_sync.rs
deleted file mode 100644
index 7394be1b..00000000
--- a/src/table/table_sync.rs
+++ /dev/null
@@ -1,898 +0,0 @@
-use rand::Rng;
-use std::collections::{BTreeMap, VecDeque};
-use std::sync::{Arc, Mutex};
-use std::time::{Duration, Instant};
-
-use futures::future::join_all;
-use futures::{pin_mut, select};
-use futures_util::future::*;
-use futures_util::stream::*;
-use serde::{Deserialize, Serialize};
-use serde_bytes::ByteBuf;
-use tokio::sync::{mpsc, watch};
-
-use garage_rpc::ring::Ring;
-use garage_util::data::*;
-use garage_util::error::Error;
-
-use crate::*;
-use crate::data::*;
-use crate::replication::*;
-
-const MAX_DEPTH: usize = 16;
-
-const TABLE_SYNC_RPC_TIMEOUT: Duration = Duration::from_secs(30);
-
-// Do anti-entropy every 10 minutes
-const SCAN_INTERVAL: Duration = Duration::from_secs(10 * 60);
-
-const CHECKSUM_CACHE_TIMEOUT: Duration = Duration::from_secs(10 * 60);
-
-pub struct TableSyncer<F: TableSchema, R: TableReplication> {
-	data: Arc<TableData<F>>,
-	aux: Arc<TableAux<F, R>>,
-
-	todo: Mutex<SyncTodo>,
-	cache: Vec<Mutex<BTreeMap<SyncRange, RangeChecksumCache>>>,
-}
-
-#[derive(Serialize, Deserialize)]
-pub(crate) enum SyncRPC {
-	GetRootChecksumRange(Hash, Hash),
-	RootChecksumRange(SyncRange),
-	Checksums(Vec<RangeChecksum>),
-	Difference(Vec<SyncRange>, Vec<Arc<ByteBuf>>),
-}
-
-struct SyncTodo {
-	todo: Vec<TodoPartition>,
-}
-
-#[derive(Debug, Clone)]
-struct TodoPartition {
-	// Partition consists in hashes between begin included and end excluded
-	begin: Hash,
-	end: Hash,
-
-	// Are we a node that stores this partition or not?
-	retain: bool,
-}
-
-// A SyncRange defines a query on the dataset stored by a node, in the following way:
-// - all items whose key are >= `begin`
-// - stopping at the first item whose key hash has at least `level` leading zero bytes (excluded)
-// - except if the first item of the range has such many leading zero bytes
-// - and stopping at `end` (excluded) if such an item is not found
-// The checksum itself does not store all of the items in the database, only the hashes of the "sub-ranges"
-// i.e. of ranges of level `level-1` that cover the same range
-// (ranges of level 0 do not exist and their hash is simply the hash of the first item >= begin)
-// See RangeChecksum for the struct that stores this information.
-#[derive(Hash, PartialEq, Eq, Debug, Clone, Serialize, Deserialize)]
-pub(crate) struct SyncRange {
-	begin: Vec<u8>,
-	end: Vec<u8>,
-	level: usize,
-}
-
-impl std::cmp::PartialOrd for SyncRange {
-	fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
-		Some(self.cmp(other))
-	}
-}
-impl std::cmp::Ord for SyncRange {
-	fn cmp(&self, other: &Self) -> std::cmp::Ordering {
-		self.begin
-			.cmp(&other.begin)
-			.then(self.level.cmp(&other.level))
-			.then(self.end.cmp(&other.end))
-	}
-}
-
-#[derive(Debug, Clone, Serialize, Deserialize)]
-pub(crate) struct RangeChecksum {
-	bounds: SyncRange,
-	children: Vec<(SyncRange, Hash)>,
-	found_limit: Option<Vec<u8>>,
-
-	#[serde(skip, default = "std::time::Instant::now")]
-	time: Instant,
-}
-
-#[derive(Debug, Clone)]
-struct RangeChecksumCache {
-	hash: Option<Hash>, // None if no children
-	found_limit: Option<Vec<u8>>,
-	time: Instant,
-}
-
-impl<F, R> TableSyncer<F, R>
-where
-	F: TableSchema + 'static,
-	R: TableReplication + 'static,
-{
-	pub(crate) fn launch(data: Arc<TableData<F>>,
-					  aux: Arc<TableAux<F, R>>) -> Arc<Self> {
-		let todo = SyncTodo{ todo: vec![] };
-
-		let syncer = Arc::new(Self {
-			data: data.clone(),
-			aux: aux.clone(),
-			todo: Mutex::new(todo),
-			cache: (0..MAX_DEPTH)
-				.map(|_| Mutex::new(BTreeMap::new()))
-				.collect::<Vec<_>>(),
-		});
-
-		let (busy_tx, busy_rx) = mpsc::unbounded_channel();
-
-		let s1 = syncer.clone();
-		aux.system.background.spawn_worker(
-			format!("table sync watcher for {}", data.name),
-			move |must_exit: watch::Receiver<bool>| s1.watcher_task(must_exit, busy_rx),
-		);
-
-		let s2 = syncer.clone();
-		aux.system.background.spawn_worker(
-			format!("table syncer for {}", data.name),
-			move |must_exit: watch::Receiver<bool>| s2.syncer_task(must_exit, busy_tx),
-		);
-
-		let s3 = syncer.clone();
-		tokio::spawn(async move {
-			tokio::time::delay_for(Duration::from_secs(20)).await;
-			s3.add_full_scan();
-		});
-
-		syncer
-	}
-
-	async fn watcher_task(
-		self: Arc<Self>,
-		mut must_exit: watch::Receiver<bool>,
-		mut busy_rx: mpsc::UnboundedReceiver<bool>,
-	) -> Result<(), Error> {
-		let mut prev_ring: Arc<Ring> = self.aux.system.ring.borrow().clone();
-		let mut ring_recv: watch::Receiver<Arc<Ring>> = self.aux.system.ring.clone();
-		let mut nothing_to_do_since = Some(Instant::now());
-
-		while !*must_exit.borrow() {
-			let s_ring_recv = ring_recv.recv().fuse();
-			let s_busy = busy_rx.recv().fuse();
-			let s_must_exit = must_exit.recv().fuse();
-			let s_timeout = tokio::time::delay_for(Duration::from_secs(1)).fuse();
-			pin_mut!(s_ring_recv, s_busy, s_must_exit, s_timeout);
-
-			select! {
-				new_ring_r = s_ring_recv => {
-					if let Some(new_ring) = new_ring_r {
-						debug!("({}) Adding ring difference to syncer todo list", self.data.name);
-						self.todo.lock().unwrap().add_ring_difference(&prev_ring, &new_ring, &self.data, &self.aux);
-						prev_ring = new_ring;
-					}
-				}
-				busy_opt = s_busy => {
-					if let Some(busy) = busy_opt {
-						if busy {
-							nothing_to_do_since = None;
-						} else {
-							if nothing_to_do_since.is_none() {
-								nothing_to_do_since = Some(Instant::now());
-							}
-						}
-					}
-				}
-				must_exit_v = s_must_exit => {
-					if must_exit_v.unwrap_or(false) {
-						break;
-					}
-				}
-				_ = s_timeout => {
-					if nothing_to_do_since.map(|t| Instant::now() - t >= SCAN_INTERVAL).unwrap_or(false) {
-						nothing_to_do_since = None;
-						debug!("({}) Adding full scan to syncer todo list", self.data.name);
-						self.add_full_scan();
-					}
-				}
-			}
-		}
-		Ok(())
-	}
-
-	pub fn add_full_scan(&self) {
-		self.todo.lock().unwrap().add_full_scan(&self.data, &self.aux);
-	}
-
-	async fn syncer_task(
-		self: Arc<Self>,
-		mut must_exit: watch::Receiver<bool>,
-		busy_tx: mpsc::UnboundedSender<bool>,
-	) -> Result<(), Error> {
-		while !*must_exit.borrow() {
-			let task = self.todo.lock().unwrap().pop_task();
-			if let Some(partition) = task {
-				busy_tx.send(true)?;
-				let res = self
-					.clone()
-					.sync_partition(&partition, &mut must_exit)
-					.await;
-				if let Err(e) = res {
-					warn!(
-						"({}) Error while syncing {:?}: {}",
-						self.data.name, partition, e
-					);
-				}
-			} else {
-				busy_tx.send(false)?;
-				tokio::time::delay_for(Duration::from_secs(1)).await;
-			}
-		}
-		Ok(())
-	}
-
-	async fn sync_partition(
-		self: Arc<Self>,
-		partition: &TodoPartition,
-		must_exit: &mut watch::Receiver<bool>,
-	) -> Result<(), Error> {
-		if partition.retain {
-			let my_id = self.aux.system.id;
-			let nodes = self
-				.aux
-				.replication
-				.write_nodes(&partition.begin, &self.aux.system)
-				.into_iter()
-				.filter(|node| *node != my_id)
-				.collect::<Vec<_>>();
-
-			debug!(
-				"({}) Preparing to sync {:?} with {:?}...",
-				self.data.name, partition, nodes
-			);
-			let root_cks = self.root_checksum(&partition.begin, &partition.end, must_exit)?;
-
-			let mut sync_futures = nodes
-				.iter()
-				.map(|node| {
-					self.clone().do_sync_with(
-						partition.clone(),
-						root_cks.clone(),
-						*node,
-						must_exit.clone(),
-					)
-				})
-				.collect::<FuturesUnordered<_>>();
-
-			let mut n_errors = 0;
-			while let Some(r) = sync_futures.next().await {
-				if let Err(e) = r {
-					n_errors += 1;
-					warn!("({}) Sync error: {}", self.data.name, e);
-				}
-			}
-			if n_errors > self.aux.replication.max_write_errors() {
-				return Err(Error::Message(format!(
-					"Sync failed with too many nodes (should have been: {:?}).",
-					nodes
-				)));
-			}
-		} else {
-			self.offload_partition(&partition.begin, &partition.end, must_exit)
-				.await?;
-		}
-
-		Ok(())
-	}
-
-	// Offload partition: this partition is not something we are storing,
-	// so send it out to all other nodes that store it and delete items locally.
-	// We don't bother checking if the remote nodes already have the items,
-	// we just batch-send everything. Offloading isn't supposed to happen very often.
-	// If any of the nodes that are supposed to store the items is unable to
-	// save them, we interrupt the process.
-	async fn offload_partition(
-		self: &Arc<Self>,
-		begin: &Hash,
-		end: &Hash,
-		must_exit: &mut watch::Receiver<bool>,
-	) -> Result<(), Error> {
-		let mut counter: usize = 0;
-
-		while !*must_exit.borrow() {
-			let mut items = Vec::new();
-
-			for item in self.data.store.range(begin.to_vec()..end.to_vec()) {
-				let (key, value) = item?;
-				items.push((key.to_vec(), Arc::new(ByteBuf::from(value.as_ref()))));
-
-				if items.len() >= 1024 {
-					break;
-				}
-			}
-
-			if items.len() > 0 {
-				let nodes = self
-					.aux
-					.replication
-					.write_nodes(&begin, &self.aux.system)
-					.into_iter()
-					.collect::<Vec<_>>();
-				if nodes.contains(&self.aux.system.id) {
-					warn!("Interrupting offload as partitions seem to have changed");
-					break;
-				}
-
-				counter += 1;
-				debug!(
-					"Offloading {} items from {:?}..{:?} ({})",
-					items.len(),
-					begin,
-					end,
-					counter
-				);
-				self.offload_items(&items, &nodes[..]).await?;
-			} else {
-				break;
-			}
-		}
-
-		Ok(())
-	}
-
-	async fn offload_items(
-		self: &Arc<Self>,
-		items: &Vec<(Vec<u8>, Arc<ByteBuf>)>,
-		nodes: &[UUID],
-	) -> Result<(), Error> {
-		let values = items.iter().map(|(_k, v)| v.clone()).collect::<Vec<_>>();
-		let update_msg = Arc::new(TableRPC::<F>::Update(values));
-
-		for res in join_all(nodes.iter().map(|to| {
-			self.aux
-				.rpc_client
-				.call_arc(*to, update_msg.clone(), TABLE_SYNC_RPC_TIMEOUT)
-		}))
-		.await
-		{
-			res?;
-		}
-
-		// All remote nodes have written those items, now we can delete them locally
-		let mut not_removed = 0;
-		for (k, v) in items.iter() {
-			if !self.data.delete_if_equal(&k[..], &v[..])? {
-				not_removed += 1;
-			}
-		}
-
-		if not_removed > 0 {
-			debug!("{} items not removed during offload because they changed in between (trying again...)", not_removed);
-		}
-
-		Ok(())
-	}
-
-	fn root_checksum(
-		self: &Arc<Self>,
-		begin: &Hash,
-		end: &Hash,
-		must_exit: &mut watch::Receiver<bool>,
-	) -> Result<RangeChecksum, Error> {
-		for i in 1..MAX_DEPTH {
-			let rc = self.range_checksum(
-				&SyncRange {
-					begin: begin.to_vec(),
-					end: end.to_vec(),
-					level: i,
-				},
-				must_exit,
-			)?;
-			if rc.found_limit.is_none() {
-				return Ok(rc);
-			}
-		}
-		Err(Error::Message(format!(
-			"Unable to compute root checksum (this should never happen)"
-		)))
-	}
-
-	fn range_checksum(
-		self: &Arc<Self>,
-		range: &SyncRange,
-		must_exit: &mut watch::Receiver<bool>,
-	) -> Result<RangeChecksum, Error> {
-		assert!(range.level != 0);
-		trace!("Call range_checksum {:?}", range);
-
-		if range.level == 1 {
-			let mut children = vec![];
-			for item in self
-				.data
-				.store
-				.range(range.begin.clone()..range.end.clone())
-			{
-				let (key, value) = item?;
-				let key_hash = blake2sum(&key[..]);
-				if children.len() > 0
-					&& key_hash.as_slice()[0..range.level]
-						.iter()
-						.all(|x| *x == 0u8)
-				{
-					trace!(
-						"range_checksum {:?} returning {} items",
-						range,
-						children.len()
-					);
-					return Ok(RangeChecksum {
-						bounds: range.clone(),
-						children,
-						found_limit: Some(key.to_vec()),
-						time: Instant::now(),
-					});
-				}
-				let item_range = SyncRange {
-					begin: key.to_vec(),
-					end: vec![],
-					level: 0,
-				};
-				children.push((item_range, blake2sum(&value[..])));
-			}
-			trace!(
-				"range_checksum {:?} returning {} items",
-				range,
-				children.len()
-			);
-			Ok(RangeChecksum {
-				bounds: range.clone(),
-				children,
-				found_limit: None,
-				time: Instant::now(),
-			})
-		} else {
-			let mut children = vec![];
-			let mut sub_range = SyncRange {
-				begin: range.begin.clone(),
-				end: range.end.clone(),
-				level: range.level - 1,
-			};
-			let mut time = Instant::now();
-			while !*must_exit.borrow() {
-				let sub_ck = self.range_checksum_cached_hash(&sub_range, must_exit)?;
-
-				if let Some(hash) = sub_ck.hash {
-					children.push((sub_range.clone(), hash));
-					if sub_ck.time < time {
-						time = sub_ck.time;
-					}
-				}
-
-				if sub_ck.found_limit.is_none() || sub_ck.hash.is_none() {
-					trace!(
-						"range_checksum {:?} returning {} items",
-						range,
-						children.len()
-					);
-					return Ok(RangeChecksum {
-						bounds: range.clone(),
-						children,
-						found_limit: None,
-						time,
-					});
-				}
-				let found_limit = sub_ck.found_limit.unwrap();
-
-				let actual_limit_hash = blake2sum(&found_limit[..]);
-				if actual_limit_hash.as_slice()[0..range.level]
-					.iter()
-					.all(|x| *x == 0u8)
-				{
-					trace!(
-						"range_checksum {:?} returning {} items",
-						range,
-						children.len()
-					);
-					return Ok(RangeChecksum {
-						bounds: range.clone(),
-						children,
-						found_limit: Some(found_limit.clone()),
-						time,
-					});
-				}
-
-				sub_range.begin = found_limit;
-			}
-			trace!("range_checksum {:?} exiting due to must_exit", range);
-			Err(Error::Message(format!("Exiting.")))
-		}
-	}
-
-	fn range_checksum_cached_hash(
-		self: &Arc<Self>,
-		range: &SyncRange,
-		must_exit: &mut watch::Receiver<bool>,
-	) -> Result<RangeChecksumCache, Error> {
-		{
-			let mut cache = self.cache[range.level].lock().unwrap();
-			if let Some(v) = cache.get(&range) {
-				if Instant::now() - v.time < CHECKSUM_CACHE_TIMEOUT {
-					return Ok(v.clone());
-				}
-			}
-			cache.remove(&range);
-		}
-
-		let v = self.range_checksum(&range, must_exit)?;
-		trace!(
-			"({}) New checksum calculated for {}-{}/{}, {} children",
-			self.data.name,
-			hex::encode(&range.begin)
-				.chars()
-				.take(16)
-				.collect::<String>(),
-			hex::encode(&range.end).chars().take(16).collect::<String>(),
-			range.level,
-			v.children.len()
-		);
-
-		let hash = if v.children.len() > 0 {
-			Some(blake2sum(&rmp_to_vec_all_named(&v)?[..]))
-		} else {
-			None
-		};
-		let cache_entry = RangeChecksumCache {
-			hash,
-			found_limit: v.found_limit,
-			time: v.time,
-		};
-
-		let mut cache = self.cache[range.level].lock().unwrap();
-		cache.insert(range.clone(), cache_entry.clone());
-		Ok(cache_entry)
-	}
-
-	async fn do_sync_with(
-		self: Arc<Self>,
-		partition: TodoPartition,
-		root_ck: RangeChecksum,
-		who: UUID,
-		mut must_exit: watch::Receiver<bool>,
-	) -> Result<(), Error> {
-		let mut todo = VecDeque::new();
-
-		// If their root checksum has level > than us, use that as a reference
-		let root_cks_resp = self
-			.aux
-			.rpc_client
-			.call(
-				who,
-				TableRPC::<F>::SyncRPC(SyncRPC::GetRootChecksumRange(
-					partition.begin.clone(),
-					partition.end.clone(),
-				)),
-				TABLE_SYNC_RPC_TIMEOUT,
-			)
-			.await?;
-		if let TableRPC::<F>::SyncRPC(SyncRPC::RootChecksumRange(range)) = root_cks_resp {
-			if range.level > root_ck.bounds.level {
-				let their_root_range_ck = self.range_checksum(&range, &mut must_exit)?;
-				todo.push_back(their_root_range_ck);
-			} else {
-				todo.push_back(root_ck);
-			}
-		} else {
-			return Err(Error::Message(format!(
-				"Invalid respone to GetRootChecksumRange RPC: {}",
-				debug_serialize(root_cks_resp)
-			)));
-		}
-
-		while !todo.is_empty() && !*must_exit.borrow() {
-			let total_children = todo.iter().map(|x| x.children.len()).fold(0, |x, y| x + y);
-			trace!(
-				"({}) Sync with {:?}: {} ({}) remaining",
-				self.data.name,
-				who,
-				todo.len(),
-				total_children
-			);
-
-			let step_size = std::cmp::min(16, todo.len());
-			let step = todo.drain(..step_size).collect::<Vec<_>>();
-
-			let rpc_resp = self
-				.aux
-				.rpc_client
-				.call(
-					who,
-					TableRPC::<F>::SyncRPC(SyncRPC::Checksums(step)),
-					TABLE_SYNC_RPC_TIMEOUT,
-				)
-				.await?;
-			if let TableRPC::<F>::SyncRPC(SyncRPC::Difference(mut diff_ranges, diff_items)) =
-				rpc_resp
-			{
-				if diff_ranges.len() > 0 || diff_items.len() > 0 {
-					info!(
-						"({}) Sync with {:?}: difference {} ranges, {} items",
-						self.data.name,
-						who,
-						diff_ranges.len(),
-						diff_items.len()
-					);
-				}
-				let mut items_to_send = vec![];
-				for differing in diff_ranges.drain(..) {
-					if differing.level == 0 {
-						items_to_send.push(differing.begin);
-					} else {
-						let checksum = self.range_checksum(&differing, &mut must_exit)?;
-						todo.push_back(checksum);
-					}
-				}
-				if diff_items.len() > 0 {
-					self.data.update_many(&diff_items[..])?;
-				}
-				if items_to_send.len() > 0 {
-					self.send_items(who, items_to_send).await?;
-				}
-			} else {
-				return Err(Error::Message(format!(
-					"Unexpected response to sync RPC checksums: {}",
-					debug_serialize(&rpc_resp)
-				)));
-			}
-		}
-		Ok(())
-	}
-
-	async fn send_items(&self, who: UUID, item_list: Vec<Vec<u8>>) -> Result<(), Error> {
-		info!(
-			"({}) Sending {} items to {:?}",
-			self.data.name,
-			item_list.len(),
-			who
-		);
-
-		let mut values = vec![];
-		for item in item_list.iter() {
-			if let Some(v) = self.data.store.get(&item[..])? {
-				values.push(Arc::new(ByteBuf::from(v.as_ref())));
-			}
-		}
-		let rpc_resp = self
-			.aux
-			.rpc_client
-			.call(who, TableRPC::<F>::Update(values), TABLE_SYNC_RPC_TIMEOUT)
-			.await?;
-		if let TableRPC::<F>::Ok = rpc_resp {
-			Ok(())
-		} else {
-			Err(Error::Message(format!(
-				"Unexpected response to RPC Update: {}",
-				debug_serialize(&rpc_resp)
-			)))
-		}
-	}
-
-	pub(crate) async fn handle_rpc(
-		self: &Arc<Self>,
-		message: &SyncRPC,
-		mut must_exit: watch::Receiver<bool>,
-	) -> Result<SyncRPC, Error> {
-		match message {
-			SyncRPC::GetRootChecksumRange(begin, end) => {
-				let root_cks = self.root_checksum(&begin, &end, &mut must_exit)?;
-				Ok(SyncRPC::RootChecksumRange(root_cks.bounds))
-			}
-			SyncRPC::Checksums(checksums) => {
-				self.handle_checksums_rpc(&checksums[..], &mut must_exit)
-					.await
-			}
-			_ => Err(Error::Message(format!("Unexpected sync RPC"))),
-		}
-	}
-
-	async fn handle_checksums_rpc(
-		self: &Arc<Self>,
-		checksums: &[RangeChecksum],
-		must_exit: &mut watch::Receiver<bool>,
-	) -> Result<SyncRPC, Error> {
-		let mut ret_ranges = vec![];
-		let mut ret_items = vec![];
-
-		for their_ckr in checksums.iter() {
-			let our_ckr = self.range_checksum(&their_ckr.bounds, must_exit)?;
-			for (their_range, their_hash) in their_ckr.children.iter() {
-				let differs = match our_ckr
-					.children
-					.binary_search_by(|(our_range, _)| our_range.cmp(&their_range))
-				{
-					Err(_) => {
-						if their_range.level >= 1 {
-							let cached_hash =
-								self.range_checksum_cached_hash(&their_range, must_exit)?;
-							cached_hash.hash.map(|h| h != *their_hash).unwrap_or(true)
-						} else {
-							true
-						}
-					}
-					Ok(i) => our_ckr.children[i].1 != *their_hash,
-				};
-				if differs {
-					ret_ranges.push(their_range.clone());
-					if their_range.level == 0 {
-						if let Some(item_bytes) =
-							self.data.store.get(their_range.begin.as_slice())?
-						{
-							ret_items.push(Arc::new(ByteBuf::from(item_bytes.to_vec())));
-						}
-					}
-				}
-			}
-			for (our_range, _hash) in our_ckr.children.iter() {
-				if let Some(their_found_limit) = &their_ckr.found_limit {
-					if our_range.begin.as_slice() > their_found_limit.as_slice() {
-						break;
-					}
-				}
-
-				let not_present = our_ckr
-					.children
-					.binary_search_by(|(their_range, _)| their_range.cmp(&our_range))
-					.is_err();
-				if not_present {
-					if our_range.level > 0 {
-						ret_ranges.push(our_range.clone());
-					}
-					if our_range.level == 0 {
-						if let Some(item_bytes) =
-							self.data.store.get(our_range.begin.as_slice())?
-						{
-							ret_items.push(Arc::new(ByteBuf::from(item_bytes.to_vec())));
-						}
-					}
-				}
-			}
-		}
-		let n_checksums = checksums
-			.iter()
-			.map(|x| x.children.len())
-			.fold(0, |x, y| x + y);
-		if ret_ranges.len() > 0 || ret_items.len() > 0 {
-			trace!(
-				"({}) Checksum comparison RPC: {} different + {} items for {} received",
-				self.data.name,
-				ret_ranges.len(),
-				ret_items.len(),
-				n_checksums
-			);
-		}
-		Ok(SyncRPC::Difference(ret_ranges, ret_items))
-	}
-
-	pub(crate) fn invalidate(self: &Arc<Self>, item_key: &[u8]) {
-		for i in 1..MAX_DEPTH {
-			let needle = SyncRange {
-				begin: item_key.to_vec(),
-				end: vec![],
-				level: i,
-			};
-			let mut cache = self.cache[i].lock().unwrap();
-			if let Some(cache_entry) = cache.range(..=needle).rev().next() {
-				if cache_entry.0.begin[..] <= *item_key && cache_entry.0.end[..] > *item_key {
-					let index = cache_entry.0.clone();
-					drop(cache_entry);
-					cache.remove(&index);
-				}
-			}
-		}
-	}
-}
-
-impl SyncTodo {
-	fn add_full_scan<F: TableSchema, R: TableReplication>(&mut self, data: &TableData<F>, aux: &TableAux<F, R>) {
-		let my_id = aux.system.id;
-
-		self.todo.clear();
-
-		let ring = aux.system.ring.borrow().clone();
-		let split_points = aux.replication.split_points(&ring);
-
-		for i in 0..split_points.len() - 1 {
-			let begin = split_points[i];
-			let end = split_points[i + 1];
-			if begin == end {
-				continue;
-			}
-
-			let nodes = aux.replication.replication_nodes(&begin, &ring);
-
-			let retain = nodes.contains(&my_id);
-			if !retain {
-				// Check if we have some data to send, otherwise skip
-				if data.store.range(begin..end).next().is_none() {
-					continue;
-				}
-			}
-
-			self.todo.push(TodoPartition { begin, end, retain });
-		}
-	}
-
-	fn add_ring_difference<F: TableSchema, R: TableReplication>(
-		&mut self,
-		old_ring: &Ring,
-		new_ring: &Ring,
-		data: &TableData<F>, aux: &TableAux<F, R>,
-	) {
-		let my_id = aux.system.id;
-
-		// If it is us who are entering or leaving the system,
-		// initiate a full sync instead of incremental sync
-		if old_ring.config.members.contains_key(&my_id)
-			!= new_ring.config.members.contains_key(&my_id)
-		{
-			self.add_full_scan(data, aux);
-			return;
-		}
-
-		let mut all_points = None
-			.into_iter()
-			.chain(aux.replication.split_points(old_ring).drain(..))
-			.chain(aux.replication.split_points(new_ring).drain(..))
-			.chain(self.todo.iter().map(|x| x.begin))
-			.chain(self.todo.iter().map(|x| x.end))
-			.collect::<Vec<_>>();
-		all_points.sort();
-		all_points.dedup();
-
-		let mut old_todo = std::mem::replace(&mut self.todo, vec![]);
-		old_todo.sort_by(|x, y| x.begin.cmp(&y.begin));
-		let mut new_todo = vec![];
-
-		for i in 0..all_points.len() - 1 {
-			let begin = all_points[i];
-			let end = all_points[i + 1];
-			let was_ours = aux
-				.replication
-				.replication_nodes(&begin, &old_ring)
-				.contains(&my_id);
-			let is_ours = aux
-				.replication
-				.replication_nodes(&begin, &new_ring)
-				.contains(&my_id);
-
-			let was_todo = match old_todo.binary_search_by(|x| x.begin.cmp(&begin)) {
-				Ok(_) => true,
-				Err(j) => {
-					(j > 0 && old_todo[j - 1].begin < end && begin < old_todo[j - 1].end)
-						|| (j < old_todo.len()
-							&& old_todo[j].begin < end && begin < old_todo[j].end)
-				}
-			};
-			if was_todo || (is_ours && !was_ours) || (was_ours && !is_ours) {
-				new_todo.push(TodoPartition {
-					begin,
-					end,
-					retain: is_ours,
-				});
-			}
-		}
-
-		self.todo = new_todo;
-	}
-
-	fn pop_task(&mut self) -> Option<TodoPartition> {
-		if self.todo.is_empty() {
-			return None;
-		}
-
-		let i = rand::thread_rng().gen_range::<usize, _, _>(0, self.todo.len());
-		if i == self.todo.len() - 1 {
-			self.todo.pop()
-		} else {
-			let replacement = self.todo.pop().unwrap();
-			let ret = std::mem::replace(&mut self.todo[i], replacement);
-			Some(ret)
-		}
-	}
-}