Refactor model stuff, including cleaner CRDTs

1 files changed, 0 insertions, 327 deletions

diff --git a/src/table/crdt.rs b/src/table/crdt.rs
deleted file mode 100644
index 4cba10ce..00000000
--- a/src/table/crdt.rs
+++ /dev/null
@@ -1,327 +0,0 @@
-//! This package provides a simple implementation of conflict-free replicated data types (CRDTs)
-//!
-//! CRDTs are a type of data structures that do not require coordination.  In other words, we can
-//! edit them in parallel, we will always find a way to merge it.
-//!
-//! A general example is a counter. Its initial value is 0.  Alice and Bob get a copy of the
-//! counter.  Alice does +1 on her copy, she reads 1.  Bob does +3 on his copy, he reads 3.  Now,
-//! it is easy to merge their counters, order does not count: we always get 4.
-//!
-//! Learn more about CRDT [on Wikipedia](https://en.wikipedia.org/wiki/Conflict-free_replicated_data_type)
-
-use serde::{Deserialize, Serialize};
-
-use garage_util::data::*;
-
-/// Definition of a CRDT - all CRDT Rust types implement this.
-///
-/// A CRDT is defined as a merge operator that respects a certain set of axioms.
-///
-/// In particular, the merge operator must be commutative, associative,
-/// idempotent, and monotonic.
-/// In other words, if `a`, `b` and `c` are CRDTs, and `⊔` denotes the merge operator,
-/// the following axioms must apply:
-///
-/// ```text
-/// a ⊔ b = b ⊔ a                   (commutativity)
-/// (a ⊔ b) ⊔ c = a ⊔ (b ⊔ c)       (associativity)
-/// (a ⊔ b) ⊔ b = a ⊔ b             (idempotence)
-/// ```
-///
-/// Moreover, the relationship `≥` defined by `a ≥ b ⇔ ∃c. a = b ⊔ c` must be a partial order.
-/// This implies a few properties such as: if `a ⊔ b ≠ a`, then there is no `c` such that `(a ⊔ b) ⊔ c = a`,
-/// as this would imply a cycle in the partial order.
-pub trait CRDT {
-	/// Merge the two datastructures according to the CRDT rules.
-	/// `self` is modified to contain the merged CRDT value. `other` is not modified.
-	///
-	/// # Arguments
-	///
-	/// * `other` - the other CRDT we wish to merge with
-	fn merge(&mut self, other: &Self);
-}
-
-/// All types that implement `Ord` (a total order) also implement a trivial CRDT
-/// defined by the merge rule: `a ⊔ b = max(a, b)`.
-impl<T> CRDT for T
-where
-	T: Ord + Clone,
-{
-	fn merge(&mut self, other: &Self) {
-		if other > self {
-			*self = other.clone();
-		}
-	}
-}
-
-// ---- LWW Register ----
-
-/// Last Write Win (LWW)
-///
-/// An LWW CRDT associates a timestamp with a value, in order to implement a
-/// time-based reconciliation rule: the most recent write wins.
-/// For completeness, the LWW reconciliation rule must also be defined for two LWW CRDTs
-/// with the same timestamp but different values.
-///
-/// In our case, we add the constraint that the value that is wrapped inside the LWW CRDT must
-/// itself be a CRDT: in the case when the timestamp does not allow us to decide on which value to
-/// keep, the merge rule of the inner CRDT is applied on the wrapped values.  (Note that all types
-/// that implement the `Ord` trait get a default CRDT implemetnation that keeps the maximum value.
-/// This enables us to use LWW directly with primitive data types such as numbers or strings. It is
-/// generally desirable in this case to never explicitly produce LWW values with the same timestamp
-/// but different inner values, as the rule to keep the maximum value isn't generally the desired
-/// semantics.)
-///
-/// As multiple computers clocks are always desynchronized,
-/// when operations are close enough, it is equivalent to
-/// take one copy and drop the other one.
-///
-/// Given that clocks are not too desynchronized, this assumption
-/// is enough for most cases, as there is few chance that two humans
-/// coordonate themself faster than the time difference between two NTP servers.
-///
-/// As a more concret example, let's suppose you want to upload a file
-/// with the same key (path) in the same bucket at the very same time.
-/// For each request, the file will be timestamped by the receiving server
-/// and may differ from what you observed with your atomic clock!
-///
-/// This scheme is used by AWS S3 or Soundcloud and often without knowing
-/// in entreprise when reconciliating databases with ad-hoc scripts.
-#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
-pub struct LWW<T> {
-	ts: u64,
-	v: T,
-}
-
-impl<T> LWW<T>
-where
-	T: CRDT,
-{
-	/// Creates a new CRDT
-	///
-	/// CRDT's internal timestamp is set with current node's clock.
-	pub fn new(value: T) -> Self {
-		Self {
-			ts: now_msec(),
-			v: value,
-		}
-	}
-
-	/// Build a new CRDT from a previous non-compatible one
-	///
-	/// Compared to new, the CRDT's timestamp is not set to now
-	/// but must be set to the previous, non-compatible, CRDT's timestamp.
-	pub fn migrate_from_raw(ts: u64, value: T) -> Self {
-		Self { ts, v: value }
-	}
-
-	/// Update the LWW CRDT while keeping some causal ordering.
-	///
-	/// The timestamp of the LWW CRDT is updated to be the current node's clock
-	/// at time of update, or the previous timestamp + 1 if that's bigger,
-	/// so that the new timestamp is always strictly larger than the previous one.
-	/// This ensures that merging the update with the old value will result in keeping
-	/// the updated value.
-	pub fn update(&mut self, new_value: T) {
-		self.ts = std::cmp::max(self.ts + 1, now_msec());
-		self.v = new_value;
-	}
-
-	/// Get the CRDT value
-	pub fn get(&self) -> &T {
-		&self.v
-	}
-
-	/// Get a mutable reference to the CRDT's value
-	///
-	/// This is usefull to mutate the inside value without changing the LWW timestamp.
-	/// When such mutation is done, the merge between two LWW values is done using the inner
-	/// CRDT's merge operation. This is usefull in the case where the inner CRDT is a large
-	/// data type, such as a map, and we only want to change a single item in the map.
-	/// To do this, we can produce a "CRDT delta", i.e. a LWW that contains only the modification.
-	/// This delta consists in a LWW with the same timestamp, and the map
-	/// inside only contains the updated value.
-	/// The advantage of such a delta is that it is much smaller than the whole map.
-	///
-	/// Avoid using this if the inner data type is a primitive type such as a number or a string,
-	/// as you will then rely on the merge function defined on `Ord` types by keeping the maximum
-	/// of both values.
-	pub fn get_mut(&mut self) -> &mut T {
-		&mut self.v
-	}
-}
-
-impl<T> CRDT for LWW<T>
-where
-	T: Clone + CRDT,
-{
-	fn merge(&mut self, other: &Self) {
-		if other.ts > self.ts {
-			self.ts = other.ts;
-			self.v = other.v.clone();
-		} else if other.ts == self.ts {
-			self.v.merge(&other.v);
-		}
-	}
-}
-
-/// Boolean, where `true` is an absorbing state
-#[derive(Clone, Copy, Debug, Serialize, Deserialize, PartialEq)]
-pub struct Bool(bool);
-
-impl Bool {
-	/// Create a new boolean with the specified value
-	pub fn new(b: bool) -> Self {
-		Self(b)
-	}
-	/// Set the boolean to true
-	pub fn set(&mut self) {
-		self.0 = true;
-	}
-	/// Get the boolean value
-	pub fn get(&self) -> bool {
-		self.0
-	}
-}
-
-impl CRDT for Bool {
-	fn merge(&mut self, other: &Self) {
-		self.0 = self.0 || other.0;
-	}
-}
-
-/// Last Write Win Map
-///
-/// This types defines a CRDT for a map from keys to values.
-/// The values have an associated timestamp, such that the last written value
-/// takes precedence over previous ones. As for the simpler `LWW` type, the value
-/// type `V` is also required to implement the CRDT trait.
-/// We do not encourage mutating the values associated with a given key
-/// without updating the timestamp, in fact at the moment we do not provide a `.get_mut()`
-/// method that would allow that.
-///
-/// Internally, the map is stored as a vector of keys and values, sorted by ascending key order.
-/// This is why the key type `K` must implement `Ord` (and also to ensure a unique serialization,
-/// such that two values can be compared for equality based on their hashes). As a consequence,
-/// insertions take `O(n)` time. This means that LWWMap should be used for reasonably small maps.
-/// However, note that even if we were using a more efficient data structure such as a `BTreeMap`,
-/// the serialization cost `O(n)` would still have to be paid at each modification, so we are
-/// actually not losing anything here.
-#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
-pub struct LWWMap<K, V> {
-	vals: Vec<(K, u64, V)>,
-}
-
-impl<K, V> LWWMap<K, V>
-where
-	K: Ord,
-	V: CRDT,
-{
-	/// Create a new empty map CRDT
-	pub fn new() -> Self {
-		Self { vals: vec![] }
-	}
-	/// Used to migrate from a map defined in an incompatible format. This produces
-	/// a map that contains a single item with the specified timestamp (copied from
-	/// the incompatible format). Do this as many times as you have items to migrate,
-	/// and put them all together using the CRDT merge operator.
-	pub fn migrate_from_raw_item(k: K, ts: u64, v: V) -> Self {
-		Self {
-			vals: vec![(k, ts, v)],
-		}
-	}
-	/// Returns a map that contains a single mapping from the specified key to the specified value.
-	/// This map is a mutator, or a delta-CRDT, such that when it is merged with the original map,
-	/// the previous value will be replaced with the one specified here.
-	/// The timestamp in the provided mutator is set to the maximum of the current system's clock
-	/// and 1 + the previous value's timestamp (if there is one), so that the new value will always
-	/// take precedence (LWW rule).
-	///
-	/// Typically, to update the value associated to a key in the map, you would do the following:
-	///
-	/// ```ignore
-	/// let my_update = my_crdt.update_mutator(key_to_modify, new_value);
-	/// my_crdt.merge(&my_update);
-	/// ```
-	///
-	/// However extracting the mutator on its own and only sending that on the network is very
-	/// interesting as it is much smaller than the whole map.
-	pub fn update_mutator(&self, k: K, new_v: V) -> Self {
-		let new_vals = match self.vals.binary_search_by(|(k2, _, _)| k2.cmp(&k)) {
-			Ok(i) => {
-				let (_, old_ts, _) = self.vals[i];
-				let new_ts = std::cmp::max(old_ts + 1, now_msec());
-				vec![(k, new_ts, new_v)]
-			}
-			Err(_) => vec![(k, now_msec(), new_v)],
-		};
-		Self { vals: new_vals }
-	}
-	/// Takes all of the values of the map and returns them. The current map is reset to the
-	/// empty map. This is very usefull to produce in-place a new map that contains only a delta
-	/// that modifies a certain value:
-	///
-	/// ```ignore
-	/// let mut a = get_my_crdt_value();
-	/// let old_a = a.take_and_clear();
-	/// a.merge(&old_a.update_mutator(key_to_modify, new_value));
-	/// put_my_crdt_value(a);
-	/// ```
-	///
-	/// Of course in this simple example we could have written simply
-	/// `pyt_my_crdt_value(a.update_mutator(key_to_modify, new_value))`,
-	/// but in the case where the map is a field in a struct for instance (as is always the case),
-	/// this becomes very handy:
-	///
-	/// ```ignore
-	/// let mut a = get_my_crdt_value();
-	/// let old_a_map = a.map_field.take_and_clear();
-	/// a.map_field.merge(&old_a_map.update_mutator(key_to_modify, new_value));
-	/// put_my_crdt_value(a);
-	/// ```
-	pub fn take_and_clear(&mut self) -> Self {
-		let vals = std::mem::replace(&mut self.vals, vec![]);
-		Self { vals }
-	}
-	/// Removes all values from the map
-	pub fn clear(&mut self) {
-		self.vals.clear();
-	}
-	/// Get a reference to the value assigned to a key
-	pub fn get(&self, k: &K) -> Option<&V> {
-		match self.vals.binary_search_by(|(k2, _, _)| k2.cmp(&k)) {
-			Ok(i) => Some(&self.vals[i].2),
-			Err(_) => None,
-		}
-	}
-	/// Gets a reference to all of the items, as a slice. Usefull to iterate on all map values.
-	/// In most case you will want to ignore the timestamp (second item of the tuple).
-	pub fn items(&self) -> &[(K, u64, V)] {
-		&self.vals[..]
-	}
-}
-
-impl<K, V> CRDT for LWWMap<K, V>
-where
-	K: Clone + Ord,
-	V: Clone + CRDT,
-{
-	fn merge(&mut self, other: &Self) {
-		for (k, ts2, v2) in other.vals.iter() {
-			match self.vals.binary_search_by(|(k2, _, _)| k2.cmp(&k)) {
-				Ok(i) => {
-					let (_, ts1, _v1) = &self.vals[i];
-					if ts2 > ts1 {
-						self.vals[i].1 = *ts2;
-						self.vals[i].2 = v2.clone();
-					} else if ts1 == ts2 {
-						self.vals[i].2.merge(&v2);
-					}
-				}
-				Err(i) => {
-					self.vals.insert(i, (k.clone(), *ts2, v2.clone()));
-				}
-			}
-		}
-	}
-}