Version Vector

Version Vectors are a fundamental concept in distributed systems that track the complete state of all peers by recording how many operations each peer has contributed.

What is a Version Vector?

A Version Vector is a map from peer IDs to operation counters, explicitly listing every peer and their operation count. It provides a complete picture of which operations are included in a version.

Example: { "peer-A": 5, "peer-B": 3 } means this version includes operations 0-4 from peer A and operations 0-2 from peer B.

Key Characteristics

• Complete information: Explicitly lists all peers and their operation counts
• Grows with peer count: Size increases as more peers join
• No dependency on history: Can determine included operations without accessing the operation log
• Enables version comparison: Can easily check if one version includes another

Basic Usage

import { LoroDoc } from "loro-crdt";
 
const doc = new LoroDoc();
doc.setPeerId("1");
const text = doc.getText("content");
text.insert(0, "Hello");
 
// Get version vector
const vv = doc.version();
console.log(vv.toJSON()); // Map { "1" => 1 }

When to Use Version Vectors

Version Vectors are ideal for:

1. Synchronization protocols - Determine what updates to send between peers
2. Network communication - Self-contained version information
3. Distributed systems - Track state across multiple nodes

Comparison with Frontiers

Conversion with Frontiers

import { LoroDoc } from "loro-crdt";
 
const doc = new LoroDoc();
const vv = doc.version();
const frontiers = doc.vvToFrontiers(vv);     // Convert to Frontiers
const backToVV = doc.frontiersToVV(frontiers); // Convert back

Related Documentation

• Frontiers - Compact version representation
• Version Tutorial - Working with versions
• Version Deep Dive - Technical details