Merkle Search Tree

This crate implements a Merkle Search Tree as described in the 2019 paper Merkle Search Trees: Efficient State-Based CRDTs in Open Networks by Alex Auvolat & François Taïani.[^cite]

When paired with CRDT-based value types, a Merkle Search Tree can act as an efficient anti-entropy primitive, allowing independent replicas to concurrently modify data within the tree with deterministic and eventual convergence across all peers.

Use It

```rust use merklesearchtree::{MerkleSearchTree, diff::diff};

// Initialise a tree using the default configuration, appropriate for most uses. let mut node_a = MerkleSearchTree::default();

// Upsert values into the tree. // // For the MST construct to be a CRDT itself, the values stored into the tree // must also be CRDTs (or at least, have deterministic conflict resolution). // Here the MST is used as an add-only set (a trivial CRDT) by using () as the // key values. nodea.upsert(&"bananas", &()); nodea.upsert(&"plátanos", &());

// Another node has differing keys. let mut nodeb = MerkleSearchTree::default(); nodeb.upsert(&"donkey", &());

// The MST root hash can be used as an efficient consistency check (comparison // is O(1) in space and time). // // In this case, both trees are inconsistent w.r.t each other, which is // indicated by their differing root hashes. assertne!(nodea.roothash(), nodeb.root_hash());

// The trees can be converged by pulling key ranges from peers - a differential // range identification implementation is included in this library: let diffrange = diff( nodeb.serialisepageranges().unwrap().intoiter(), nodea.serialisepageranges().unwrap().into_iter() );

// In this case, node B can obtain the missing/differing keys in node A by // requesting keys within the computed diff range (inclusive): assertmatches::assertmatches!(diffrange.asslice(), [range] => { asserteq!(range.start(), &"bananas"); asserteq!(range.end(), &"plátanos"); }); ```

State-Based CRDTs in Open Networks. SRDS 2019 - 38th IEEE International
Symposium on Reliable Distributed Systems, Oct 2019, Lyon, France. pp.1-10,
⟨10.1109/SRDS.2019.00032⟩. ⟨hal-02303490⟩