First implementation of K2V (#293)

**Specification:**

View spec at [this URL](https://git.deuxfleurs.fr/Deuxfleurs/garage/src/branch/k2v/doc/drafts/k2v-spec.md)

- [x] Specify the structure of K2V triples
- [x] Specify the DVVS format used for causality detection
- [x] Specify the K2V index (just a counter of number of values per partition key)
- [x] Specify single-item endpoints: ReadItem, InsertItem, DeleteItem
- [x] Specify index endpoint: ReadIndex
- [x] Specify multi-item endpoints: InsertBatch, ReadBatch, DeleteBatch
- [x] Move to JSON objects instead of tuples
- [x] Specify endpoints for polling for updates on single values (PollItem)

**Implementation:**

- [x] Table for K2V items, causal contexts
- [x] Indexing mechanism and table for K2V index
- [x] Make API handlers a bit more generic
- [x] K2V API endpoint
- [x] K2V API router
- [x] ReadItem
- [x] InsertItem
- [x] DeleteItem
- [x] PollItem
- [x] ReadIndex
- [x] InsertBatch
- [x] ReadBatch
- [x] DeleteBatch

**Testing:**

- [x] Just a simple Python script that does some requests to check visually that things are going right (does not contain parsing of results or assertions on returned values)
- [x] Actual tests:
  - [x] Adapt testing framework
  - [x] Simple test with InsertItem + ReadItem
  - [x] Test with several Insert/Read/DeleteItem + ReadIndex
  - [x] Test all combinations of return formats for ReadItem
  - [x] Test with ReadBatch, InsertBatch, DeleteBatch
  - [x] Test with PollItem
  - [x] Test error codes
- [ ] Fix most broken stuff
  - [x] test PollItem broken randomly
  - [x] when invalid causality tokens are given, errors should be 4xx not 5xx

**Improvements:**

- [x] Descending range queries
  - [x] Specify
  - [x] Implement
  - [x] Add test
- [x] Batch updates to index counter
- [x] Put K2V behind `k2v` feature flag

Co-authored-by: Alex Auvolat <alex@adnab.me>
Reviewed-on: https://git.deuxfleurs.fr/Deuxfleurs/garage/pulls/293
Co-authored-by: Alex <alex@adnab.me>
Co-committed-by: Alex <alex@adnab.me>

1 files changed, 291 insertions, 0 deletions

diff --git a/src/model/k2v/item_table.rs b/src/model/k2v/item_table.rs
new file mode 100644
index 00000000..8b7cc08a
--- /dev/null
+++ b/src/model/k2v/item_table.rs
@@ -0,0 +1,291 @@
+use serde::{Deserialize, Serialize};
+use std::collections::BTreeMap;
+use std::sync::Arc;
+
+use garage_util::data::*;
+
+use garage_table::crdt::*;
+use garage_table::*;
+
+use crate::index_counter::*;
+use crate::k2v::causality::*;
+use crate::k2v::counter_table::*;
+use crate::k2v::poll::*;
+
+#[derive(PartialEq, Clone, Debug, Serialize, Deserialize)]
+pub struct K2VItem {
+	pub partition: K2VItemPartition,
+	pub sort_key: String,
+
+	items: BTreeMap<K2VNodeId, DvvsEntry>,
+}
+
+#[derive(PartialEq, Clone, Debug, Serialize, Deserialize, Hash, Eq)]
+pub struct K2VItemPartition {
+	pub bucket_id: Uuid,
+	pub partition_key: String,
+}
+
+#[derive(PartialEq, Clone, Debug, Serialize, Deserialize)]
+struct DvvsEntry {
+	t_discard: u64,
+	values: Vec<(u64, DvvsValue)>,
+}
+
+#[derive(PartialEq, Clone, Debug, Serialize, Deserialize)]
+pub enum DvvsValue {
+	Value(#[serde(with = "serde_bytes")] Vec<u8>),
+	Deleted,
+}
+
+impl K2VItem {
+	/// Creates a new K2VItem when no previous entry existed in the db
+	pub fn new(bucket_id: Uuid, partition_key: String, sort_key: String) -> Self {
+		Self {
+			partition: K2VItemPartition {
+				bucket_id,
+				partition_key,
+			},
+			sort_key,
+			items: BTreeMap::new(),
+		}
+	}
+	/// Updates a K2VItem with a new value or a deletion event
+	pub fn update(
+		&mut self,
+		this_node: Uuid,
+		context: &Option<CausalContext>,
+		new_value: DvvsValue,
+	) {
+		if let Some(context) = context {
+			for (node, t_discard) in context.vector_clock.iter() {
+				if let Some(e) = self.items.get_mut(node) {
+					e.t_discard = std::cmp::max(e.t_discard, *t_discard);
+				} else {
+					self.items.insert(
+						*node,
+						DvvsEntry {
+							t_discard: *t_discard,
+							values: vec![],
+						},
+					);
+				}
+			}
+		}
+
+		self.discard();
+
+		let node_id = make_node_id(this_node);
+		let e = self.items.entry(node_id).or_insert(DvvsEntry {
+			t_discard: 0,
+			values: vec![],
+		});
+		let t_prev = e.max_time();
+		e.values.push((t_prev + 1, new_value));
+	}
+
+	/// Extract the causality context of a K2V Item
+	pub fn causal_context(&self) -> CausalContext {
+		let mut cc = CausalContext::new_empty();
+		for (node, ent) in self.items.iter() {
+			cc.vector_clock.insert(*node, ent.max_time());
+		}
+		cc
+	}
+
+	/// Extract the list of values
+	pub fn values(&'_ self) -> Vec<&'_ DvvsValue> {
+		let mut ret = vec![];
+		for (_, ent) in self.items.iter() {
+			for (_, v) in ent.values.iter() {
+				if !ret.contains(&v) {
+					ret.push(v);
+				}
+			}
+		}
+		ret
+	}
+
+	fn discard(&mut self) {
+		for (_, ent) in self.items.iter_mut() {
+			ent.discard();
+		}
+	}
+
+	// returns counters: (non-deleted entries, conflict entries, non-tombstone values, bytes used)
+	fn stats(&self) -> (i64, i64, i64, i64) {
+		let values = self.values();
+
+		let n_entries = if self.is_tombstone() { 0 } else { 1 };
+		let n_conflicts = if values.len() > 1 { 1 } else { 0 };
+		let n_values = values
+			.iter()
+			.filter(|v| matches!(v, DvvsValue::Value(_)))
+			.count() as i64;
+		let n_bytes = values
+			.iter()
+			.map(|v| match v {
+				DvvsValue::Deleted => 0,
+				DvvsValue::Value(v) => v.len() as i64,
+			})
+			.sum();
+
+		(n_entries, n_conflicts, n_values, n_bytes)
+	}
+}
+
+impl DvvsEntry {
+	fn max_time(&self) -> u64 {
+		self.values
+			.iter()
+			.fold(self.t_discard, |acc, (vts, _)| std::cmp::max(acc, *vts))
+	}
+
+	fn discard(&mut self) {
+		self.values = std::mem::take(&mut self.values)
+			.into_iter()
+			.filter(|(t, _)| *t > self.t_discard)
+			.collect::<Vec<_>>();
+	}
+}
+
+impl Crdt for K2VItem {
+	fn merge(&mut self, other: &Self) {
+		for (node, e2) in other.items.iter() {
+			if let Some(e) = self.items.get_mut(node) {
+				e.merge(e2);
+			} else {
+				self.items.insert(*node, e2.clone());
+			}
+		}
+	}
+}
+
+impl Crdt for DvvsEntry {
+	fn merge(&mut self, other: &Self) {
+		self.t_discard = std::cmp::max(self.t_discard, other.t_discard);
+		self.discard();
+
+		let t_max = self.max_time();
+		for (vt, vv) in other.values.iter() {
+			if *vt > t_max {
+				self.values.push((*vt, vv.clone()));
+			}
+		}
+	}
+}
+
+impl PartitionKey for K2VItemPartition {
+	fn hash(&self) -> Hash {
+		use blake2::{Blake2b, Digest};
+
+		let mut hasher = Blake2b::new();
+		hasher.update(self.bucket_id.as_slice());
+		hasher.update(self.partition_key.as_bytes());
+		let mut hash = [0u8; 32];
+		hash.copy_from_slice(&hasher.finalize()[..32]);
+		hash.into()
+	}
+}
+
+impl Entry<K2VItemPartition, String> for K2VItem {
+	fn partition_key(&self) -> &K2VItemPartition {
+		&self.partition
+	}
+	fn sort_key(&self) -> &String {
+		&self.sort_key
+	}
+	fn is_tombstone(&self) -> bool {
+		self.values()
+			.iter()
+			.all(|v| matches!(v, DvvsValue::Deleted))
+	}
+}
+
+pub struct K2VItemTable {
+	pub(crate) counter_table: Arc<IndexCounter<K2VCounterTable>>,
+	pub(crate) subscriptions: Arc<SubscriptionManager>,
+}
+
+#[derive(Clone, Copy, Debug, Serialize, Deserialize)]
+pub struct ItemFilter {
+	pub exclude_only_tombstones: bool,
+	pub conflicts_only: bool,
+}
+
+impl TableSchema for K2VItemTable {
+	const TABLE_NAME: &'static str = "k2v_item";
+
+	type P = K2VItemPartition;
+	type S = String;
+	type E = K2VItem;
+	type Filter = ItemFilter;
+
+	fn updated(&self, old: Option<&Self::E>, new: Option<&Self::E>) {
+		// 1. Count
+		let (old_entries, old_conflicts, old_values, old_bytes) = match old {
+			None => (0, 0, 0, 0),
+			Some(e) => e.stats(),
+		};
+		let (new_entries, new_conflicts, new_values, new_bytes) = match new {
+			None => (0, 0, 0, 0),
+			Some(e) => e.stats(),
+		};
+
+		let count_pk = old
+			.map(|e| e.partition.bucket_id)
+			.unwrap_or_else(|| new.unwrap().partition.bucket_id);
+		let count_sk = old
+			.map(|e| &e.partition.partition_key)
+			.unwrap_or_else(|| &new.unwrap().partition.partition_key);
+
+		if let Err(e) = self.counter_table.count(
+			&count_pk,
+			count_sk,
+			&[
+				(ENTRIES, new_entries - old_entries),
+				(CONFLICTS, new_conflicts - old_conflicts),
+				(VALUES, new_values - old_values),
+				(BYTES, new_bytes - old_bytes),
+			],
+		) {
+			error!("Could not update K2V counter for bucket {:?} partition {}; counts will now be inconsistent. {}", count_pk, count_sk, e);
+		}
+
+		// 2. Notify
+		if let Some(new_ent) = new {
+			self.subscriptions.notify(new_ent);
+		}
+	}
+
+	#[allow(clippy::nonminimal_bool)]
+	fn matches_filter(entry: &Self::E, filter: &Self::Filter) -> bool {
+		let v = entry.values();
+		!(filter.conflicts_only && v.len() < 2)
+			&& !(filter.exclude_only_tombstones && entry.is_tombstone())
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn test_dvvsentry_merge_simple() {
+		let e1 = DvvsEntry {
+			t_discard: 4,
+			values: vec![
+				(5, DvvsValue::Value(vec![15])),
+				(6, DvvsValue::Value(vec![16])),
+			],
+		};
+		let e2 = DvvsEntry {
+			t_discard: 5,
+			values: vec![(6, DvvsValue::Value(vec![16])), (7, DvvsValue::Deleted)],
+		};
+
+		let mut e3 = e1.clone();
+		e3.merge(&e2);
+		assert_eq!(e2, e3);
+	}
+}