Crate mdcs_core 

mdcs-core

Core CRDT types and traits for the Carnelia Merkle-Delta CRDT Store.

This crate provides the foundational building blocks for conflict-free replicated data types (CRDTs). Every type implements the Lattice trait, which models a join-semilattice and guarantees Strong Eventual Consistency: all replicas converge to the same state regardless of message order.

Mathematical Foundation

A join-semilattice $(S, \sqcup)$ satisfies three properties:

Property	Definition
Commutativity	$a \sqcup b = b \sqcup a$
Associativity	$(a \sqcup b) \sqcup c = a \sqcup (b \sqcup c)$
Idempotence	$a \sqcup a = a$

These guarantees mean that updates can be applied in any order, any number of times, and the result is always deterministic.

CRDT Types

Type	Module	Description
GSet	gset	Grow-only set — elements can only be added
ORSet	orset	Observed-Remove set — add-wins semantics
PNCounter	pncounter	Increment/decrement counter
LWWRegister	lwwreg	Last-Writer-Wins register
MVRegister	mvreg	Multi-Value register — preserves concurrent writes
CRDTMap	map	Composable map with shared causal context

Quick Start

use mdcs_core::prelude::*;

// Create two replicas of a grow-only set
let mut a = GSet::new();
let mut b = GSet::new();

a.insert(1);
b.insert(2);

// Merge — order doesn't matter
let merged = a.join(&b);
assert!(merged.contains(&1));
assert!(merged.contains(&2));

Feature: Delta-State Support

Types that implement DeltaCRDT support efficient delta-state replication. Instead of shipping full state, only incremental changes (deltas) are transmitted. See the mdcs-delta crate for the anti-entropy protocol that drives synchronization.

Re-exports

pub use gset::GSet;

pub use lattice::DeltaCRDT;

pub use lattice::Lattice;

pub use lwwreg::LWWRegister;

pub use map::CRDTMap;

pub use map::CausalContext;

pub use map::MapValue;

pub use mvreg::MVRegister;

pub use orset::ORSet;

pub use pncounter::PNCounter;

Modules

gset

Grow-only Set - elements can only be added, never removed This is the simplest useful CRDT and a good starting point.

lattice

Join-semilattice trait - the mathematical foundation of CRDTs

lwwreg

Last-Write-Wins (LWW) Register CRDT

map

Map CRDT - A composable container for nested CRDTs

mvreg

Multi-Value Register CRDT

orset

Observed-Remove Set (OR-Set / Add-Wins Set)

pncounter

PN-Counter (Positive-Negative Counter) CRDT

prelude

Prelude module — import everything you need with use mdcs_core::prelude::*.