Make K2V item timestamps globally increasing on each node

1 files changed, 41 insertions, 4 deletions

diff --git a/src/model/k2v/rpc.rs b/src/model/k2v/rpc.rs
index 8860676b..e5497215 100644
--- a/src/model/k2v/rpc.rs
+++ b/src/model/k2v/rpc.rs
@@ -6,7 +6,8 @@
 //! mean the vector clock gets much larger than needed).
 
 use std::collections::HashMap;
-use std::sync::Arc;
+use std::convert::TryInto;
+use std::sync::{Arc, Mutex};
 use std::time::Duration;
 
 use async_trait::async_trait;
@@ -15,9 +16,12 @@ use futures::StreamExt;
 use serde::{Deserialize, Serialize};
 use tokio::select;
 
+use garage_db as db;
+
 use garage_util::crdt::*;
 use garage_util::data::*;
 use garage_util::error::*;
+use garage_util::time::now_msec;
 
 use garage_rpc::system::System;
 use garage_rpc::*;
@@ -29,6 +33,8 @@ use crate::k2v::causality::*;
 use crate::k2v::item_table::*;
 use crate::k2v::sub::*;
 
+const TIMESTAMP_KEY: &'static [u8] = b"timestamp";
+
 /// RPC messages for K2V
 #[derive(Debug, Serialize, Deserialize)]
 enum K2VRpc {
@@ -59,6 +65,7 @@ impl Rpc for K2VRpc {
 pub struct K2VRpcHandler {
 	system: Arc<System>,
 	item_table: Arc<Table<K2VItemTable, TableShardedReplication>>,
+	local_timestamp_tree: Mutex<db::Tree>,
 	endpoint: Arc<Endpoint<K2VRpc, Self>>,
 	subscriptions: Arc<SubscriptionManager>,
 }
@@ -66,14 +73,19 @@ pub struct K2VRpcHandler {
 impl K2VRpcHandler {
 	pub fn new(
 		system: Arc<System>,
+		db: &db::Db,
 		item_table: Arc<Table<K2VItemTable, TableShardedReplication>>,
 		subscriptions: Arc<SubscriptionManager>,
 	) -> Arc<Self> {
+		let local_timestamp_tree = db
+			.open_tree("k2v_local_timestamp")
+			.expect("Unable to open DB tree for k2v local timestamp");
 		let endpoint = system.netapp.endpoint("garage_model/k2v/Rpc".to_string());
 
 		let rpc_handler = Arc::new(Self {
 			system,
 			item_table,
+			local_timestamp_tree: Mutex::new(local_timestamp_tree),
 			endpoint,
 			subscriptions,
 		});
@@ -273,9 +285,22 @@ impl K2VRpcHandler {
 	}
 
 	fn local_insert(&self, item: &InsertedItem) -> Result<Option<K2VItem>, Error> {
+		// Using a mutex on the local_timestamp_tree is not strictly necessary,
+		// but it helps to not try to do several inserts at the same time,
+		// which would create transaction conflicts and force many useless retries.
+		let local_timestamp_tree = self.local_timestamp_tree.lock().unwrap();
+
+		let now = now_msec();
+
 		self.item_table
 			.data
-			.update_entry_with(&item.partition, &item.sort_key, |ent| {
+			.update_entry_with(&item.partition, &item.sort_key, |tx, ent| {
+				let old_local_timestamp = tx
+					.get(&local_timestamp_tree, TIMESTAMP_KEY)?
+					.and_then(|x| x.try_into().ok())
+					.map(u64::from_be_bytes)
+					.unwrap_or_default();
+
 				let mut ent = ent.unwrap_or_else(|| {
 					K2VItem::new(
 						item.partition.bucket_id,
@@ -283,8 +308,20 @@ impl K2VRpcHandler {
 						item.sort_key.clone(),
 					)
 				});
-				ent.update(self.system.id, &item.causal_context, item.value.clone());
-				ent
+				let new_local_timestamp = ent.update(
+					self.system.id,
+					&item.causal_context,
+					item.value.clone(),
+					std::cmp::max(old_local_timestamp, now),
+				);
+
+				tx.insert(
+					&local_timestamp_tree,
+					TIMESTAMP_KEY,
+					u64::to_be_bytes(new_local_timestamp),
+				)?;
+
+				Ok(ent)
 			})
 	}