Not fully tested: new multi-dc MagLev

script/simulate_ring.py

@@ -262,21 +262,21 @@ if __name__ == "__main__":
 
     print("------")
     print("method 2 (custom ring)")
-    nodes = [('digitale', 'atuin', 4),
-             ('drosera', 'atuin', 4),
-             ('datura', 'atuin', 4),
-             ('io', 'jupiter', 8)]
-    nodes2 = [('digitale', 'atuin', 8),
-             ('drosera', 'atuin', 8),
-             ('datura', 'atuin', 8),
-             ('io', 'jupiter', 16),
-             ('isou', 'jupiter', 8),
-             ('mini', 'grog', 4),
-             ('mixi', 'grog', 4),
-             ('moxi', 'grog', 4),
-             ('modi', 'grog', 4),
-             ('geant', 'grisou', 16),
-             ('gipsie', 'grisou', 16),
+    nodes = [('digitale', 'atuin', 1),
+             ('drosera', 'atuin', 1),
+             ('datura', 'atuin', 1),
+             ('io', 'jupiter', 2)]
+    nodes2 = [('digitale', 'atuin', 2),
+             ('drosera', 'atuin', 2),
+             ('datura', 'atuin', 2),
+             ('io', 'jupiter', 4),
+             ('isou', 'jupiter', 2),
+             ('mini', 'grog', 1),
+             ('mixi', 'grog', 1),
+             ('moxi', 'grog', 1),
+             ('modi', 'grog', 1),
+             ('geant', 'grisou', 4),
+             ('gipsie', 'grisou', 4),
              ]
     evaluate_method(method2, nodes2)
 

src/rpc/membership.rs

@@ -218,12 +218,7 @@ impl System {
 				.unwrap_or("<invalid utf-8>".to_string()),
 		};
 
-		let mut ring = Ring {
-			config: net_config,
-			ring: Vec::new(),
-			n_datacenters: 0,
-		};
-		ring.rebuild_ring();
+		let ring = Ring::new(net_config);
 		let (update_ring, ring) = watch::channel(Arc::new(ring));
 
 		let rpc_path = MEMBERSHIP_RPC_PATH.to_string();
@@ -531,10 +526,7 @@ impl System {
 		let ring: Arc<Ring> = self.ring.borrow().clone();
 
 		if adv.version > ring.config.version {
-			let mut ring = ring.as_ref().clone();
-
-			ring.config = adv.clone();
-			ring.rebuild_ring();
+			let ring = Ring::new(adv.clone());
 			update_lock.1.broadcast(Arc::new(ring))?;
 			drop(update_lock);
 

src/rpc/ring.rs

@@ -1,9 +1,22 @@
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
+use std::convert::TryInto;
 
 use serde::{Deserialize, Serialize};
 
 use garage_util::data::*;
 
+// TODO: make this constant parametrizable in the config file
+// For deployments with many nodes it might make sense to bump
+// it up to 10.
+// Maximum value : 16
+pub const PARTITION_BITS: usize = 8;
+
+const PARTITION_MASK_U16: u16 = ((1 << PARTITION_BITS) - 1) << (16 - PARTITION_BITS);
+
+// TODO: make this constant paraetrizable in the config file
+// (most deployments use a replication factor of 3, so...)
+pub const MAX_REPLICATION: usize = 3;
+
 #[derive(Clone, Debug, Serialize, Deserialize)]
 pub struct NetworkConfig {
 	pub members: HashMap<UUID, NetworkConfigEntry>,
@@ -30,96 +43,150 @@ pub struct NetworkConfigEntry {
 pub struct Ring {
 	pub config: NetworkConfig,
 	pub ring: Vec<RingEntry>,
-	pub n_datacenters: usize,
 }
 
 #[derive(Clone, Debug)]
 pub struct RingEntry {
 	pub location: Hash,
-	pub node: UUID,
-	datacenter: usize,
+	pub nodes: [UUID; MAX_REPLICATION],
 }
 
 impl Ring {
-	pub(crate) fn rebuild_ring(&mut self) {
-		let mut new_ring = vec![];
-		let mut datacenters = vec![];
+	pub(crate) fn new(config: NetworkConfig) -> Self {
+		// Create a vector of partition indices (0 to 2**PARTITION_BITS-1)
+		let partitions_idx = (0usize..(1usize << PARTITION_BITS)).collect::<Vec<_>>();
 
-		for (id, config) in self.config.members.iter() {
-			let datacenter = &config.datacenter;
+		let datacenters = config
+			.members
+			.iter()
+			.map(|(_id, info)| info.datacenter.as_str())
+			.collect::<HashSet<&str>>();
+		let n_datacenters = datacenters.len();
 
-			if !datacenters.contains(datacenter) {
-				datacenters.push(datacenter.to_string());
+		// Prepare ring
+		let mut partitions: Vec<Vec<(&UUID, &NetworkConfigEntry)>> = partitions_idx
+			.iter()
+			.map(|_i| Vec::new())
+			.collect::<Vec<_>>();
+
+		// Create MagLev priority queues for each node
+		let mut queues = config
+			.members
+			.iter()
+			.map(|(node_id, node_info)| {
+				let mut parts = partitions_idx
+					.iter()
+					.map(|i| {
+						let part_data =
+							[&u16::to_be_bytes(*i as u16)[..], node_id.as_slice()].concat();
+						(*i, fasthash(&part_data[..]))
+					})
+					.collect::<Vec<_>>();
+				parts.sort_by_key(|(_i, h)| *h);
+				let parts_i = parts.iter().map(|(i, _h)| *i).collect::<Vec<_>>();
+				(node_id, node_info, parts_i, 0)
+			})
+			.collect::<Vec<_>>();
+
+		let max_toktok = config
+			.members
+			.iter()
+			.map(|(_, node_info)| node_info.n_tokens)
+			.fold(0, std::cmp::max);
+
+		// Fill up ring
+		for rep in 0..MAX_REPLICATION {
+			queues.sort_by_key(|(ni, _np, _q, _p)| {
+				let queue_data = [&u16::to_be_bytes(rep as u16)[..], ni.as_slice()].concat();
+				fasthash(&queue_data[..])
+			});
+
+			for (_, _, _, pos) in queues.iter_mut() {
+				*pos = 0;
 			}
-			let datacenter_idx = datacenters
-				.iter()
-				.enumerate()
-				.find(|(_, dc)| *dc == datacenter)
-				.unwrap()
-				.0;
 
-			for i in 0..config.n_tokens {
-				let location = sha256sum(format!("{} {}", hex::encode(&id), i).as_bytes());
-
-				new_ring.push(RingEntry {
-					location: location.into(),
-					node: *id,
-					datacenter: datacenter_idx,
-				})
+			let mut remaining = partitions_idx.len();
+			while remaining > 0 {
+				let remaining0 = remaining;
+				for toktok in 0..max_toktok {
+					for (node_id, node_info, q, pos) in queues.iter_mut() {
+						if toktok >= node_info.n_tokens {
+							continue;
+						}
+						for pos2 in *pos..q.len() {
+							let qv = q[pos2];
+							if partitions[qv].len() != rep {
+								continue;
+							}
+							let p_dcs = partitions[qv]
+								.iter()
+								.map(|(_id, info)| info.datacenter.as_str())
+								.collect::<HashSet<&str>>();
+							if !partitions[qv]
+								.iter()
+								.any(|(_id, i)| *i.datacenter == node_info.datacenter)
+								|| (p_dcs.len() == n_datacenters
+									&& !partitions[qv].iter().any(|(id, _i)| id == node_id))
+							{
+								partitions[qv].push((node_id, node_info));
+								remaining -= 1;
+								*pos = pos2 + 1;
+								break;
+							}
+						}
+					}
+				}
+				if remaining == remaining0 {
+					// No progress made, exit
+					warn!("Could not build ring, not enough nodes configured.");
+					return Self {
+						config,
+						ring: vec![],
+					};
+				}
 			}
 		}
 
-		new_ring.sort_unstable_by(|x, y| x.location.cmp(&y.location));
-		self.ring = new_ring;
-		self.n_datacenters = datacenters.len();
+		let ring = partitions
+			.iter()
+			.enumerate()
+			.map(|(i, nodes)| {
+				let top = (i as u16) << (16 - PARTITION_BITS);
+				let mut hash = [0u8; 32];
+				hash[0..2].copy_from_slice(&u16::to_be_bytes(top)[..]);
+				let nodes = nodes.iter().map(|(id, _info)| **id).collect::<Vec<UUID>>();
+				RingEntry {
+					location: hash.into(),
+					nodes: nodes.try_into().unwrap(),
+				}
+			})
+			.collect::<Vec<_>>();
 
-		// eprintln!("RING: --");
-		// for e in self.ring.iter() {
-		// 	eprintln!("{:?}", e);
-		// }
-		// eprintln!("END --");
+		eprintln!("RING: --");
+		for e in ring.iter() {
+			eprintln!("{:?}", e);
+		}
+		eprintln!("END --");
+
+		Self { config, ring }
 	}
 
 	pub fn walk_ring(&self, from: &Hash, n: usize) -> Vec<UUID> {
-		if n >= self.config.members.len() {
-			return self.config.members.keys().cloned().collect::<Vec<_>>();
+		if self.ring.len() != 1 << PARTITION_BITS {
+			warn!("Ring not yet ready, read/writes will be lost");
+			return vec![];
 		}
 
-		let start = match self.ring.binary_search_by(|x| x.location.cmp(from)) {
-			Ok(i) => i,
-			Err(i) => {
-				if i == 0 {
-					self.ring.len() - 1
-				} else {
-					i - 1
-				}
-			}
-		};
+		let top = u16::from_be_bytes(from.as_slice()[0..2].try_into().unwrap());
 
-		self.walk_ring_from_pos(start, n)
-	}
+		let partition_idx = (top >> (16 - PARTITION_BITS)) as usize;
+		let partition = &self.ring[partition_idx];
 
-	fn walk_ring_from_pos(&self, start: usize, n: usize) -> Vec<UUID> {
-		if n >= self.config.members.len() {
-			return self.config.members.keys().cloned().collect::<Vec<_>>();
-		}
+		let partition_top =
+			u16::from_be_bytes(partition.location.as_slice()[0..2].try_into().unwrap());
+		assert!(partition_top & PARTITION_MASK_U16 == top & PARTITION_MASK_U16);
 
-		let mut ret = vec![];
-		let mut datacenters = vec![];
-
-		let mut delta = 0;
-		while ret.len() < n {
-			let i = (start + delta) % self.ring.len();
-			delta += 1;
-
-			if !datacenters.contains(&self.ring[i].datacenter) {
-				ret.push(self.ring[i].node);
-				datacenters.push(self.ring[i].datacenter);
-			} else if datacenters.len() == self.n_datacenters && !ret.contains(&self.ring[i].node) {
-				ret.push(self.ring[i].node);
-			}
-		}
-
-		ret
+		assert!(n <= partition.nodes.len());
+		partition.nodes[..n].iter().cloned().collect::<Vec<_>>()
 	}
 }

src/table/table_sharded.rs

@@ -44,7 +44,6 @@ 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);
 		}