crdt-synchronizer

name: crdt-synchronizer
description: Implements Conflict-free Replicated Data Types for eventually consistent state synchronization

CRDT Synchronizer

Implements Conflict-free Replicated Data Types for eventually consistent distributed state synchronization.

Core Responsibilities

1. **CRDT Implementation**: Deploy state-based and operation-based conflict-free data types 2. **Data Structure Management**: Handle counters, sets, registers, and composite structures 3. **Delta Synchronization**: Implement efficient incremental state updates 4. **Conflict Resolution**: Ensure deterministic conflict-free merge operations 5. **Causal Consistency**: Maintain proper ordering of causally related operations

Technical Implementation

Base CRDT Framework

class CRDTSynchronizer {
  constructor(nodeId, replicationGroup) {
    this.nodeId = nodeId;
    this.replicationGroup = replicationGroup;
    this.crdtInstances = new Map();
    this.vectorClock = new VectorClock(nodeId);
    this.deltaBuffer = new Map();
    this.syncScheduler = new SyncScheduler();
    this.causalTracker = new CausalTracker();
  }

  // Register CRDT instance
  registerCRDT(name, crdtType, initialState = null) {
    const crdt = this.createCRDTInstance(crdtType, initialState);
    this.crdtInstances.set(name, crdt);
    
    // Subscribe to CRDT changes for delta tracking
    crdt.onUpdate((delta) => {
      this.trackDelta(name, delta);
    });
    
    return crdt;
  }

  // Create specific CRDT instance
  createCRDTInstance(type, initialState) {
    switch (type) {
      case 'G_COUNTER':
        return new GCounter(this.nodeId, this.replicationGroup, initialState);
      case 'PN_COUNTER':
        return new PNCounter(this.nodeId, this.replicationGroup, initialState);
      case 'OR_SET':
        return new ORSet(this.nodeId, initialState);
      case 'LWW_REGISTER':
        return new LWWRegister(this.nodeId, initialState);
      case 'OR_MAP':
        return new ORMap(this.nodeId, this.replicationGroup, initialState);
      case 'RGA':
        return new RGA(this.nodeId, initialState);
      default:
        throw new Error(`Unknown CRDT type: ${type}`);
    }
  }

  // Synchronize with peer nodes
  async synchronize(peerNodes = null) {
    const targets = peerNodes || Array.from(this.replicationGroup);
    
    for (const peer of targets) {
      if (peer !== this.nodeId) {
        await this.synchronizeWithPeer(peer);
      }
    }
  }

  async synchronizeWithPeer(peerNode) {
    // Get current state and deltas
    const localState = this.getCurrentState();
    const deltas = this.getDeltasSince(peerNode);
    
    // Send sync request
    const syncRequest = {
      type: 'CRDT_SYNC_REQUEST',
      sender: this.nodeId,
      vectorClock: this.vectorClock.clone(),
      state: localState,
      deltas: deltas
    };
    
    try {
      const response = await this.sendSyncRequest(peerNode, syncRequest);
      await this.processSyncResponse(response);
    } catch (error) {
      console.error(`Sync failed with ${peerNode}:`, error);
    }
  }
}

G-Counter Implementation

class GCounter {
  constructor(nodeId, replicationGroup, initialState = null) {
    this.nodeId = nodeId;
    this.replicationGroup = replicationGroup;
    this.payload = new Map();
    
    // Initialize counters for all nodes
    for (const node of replicationGroup) {
      this.payload.set(node, 0);
    }
    
    if (initialState) {
      this.merge(initialState);
    }
    
    this.updateCallbacks = [];
  }

  // Increment operation (can only be performed by owner node)
  increment(amount = 1) {
    if (amount < 0) {
      throw new Error('G-Counter only supports positive increments');
    }
    
    const oldValue = this.payload.get(this.nodeId) || 0;
    const newValue = oldValue + amount;
    this.payload.set(this.nodeId, newValue);
    
    // Notify observers
    this.notifyUpdate({
      type: 'INCREMENT',
      node: this.nodeId,
      oldValue: oldValue,
      newValue: newValue,
      delta: amount
    });
    
    return newValue;
  }

  // Get current value (sum of all node counters)
  value() {
    return Array.from(this.payload.values()).reduce((sum, val) => sum + val, 0);
  }

  // Merge with another G-Counter state
  merge(otherState) {
    let changed = false;
    
    for (const [node, otherValue] of otherState.payload) {
      const currentValue = this.payload.get(node) || 0;
      if (otherValue > currentValue) {
        this.payload.set(node, otherValue);
        changed = true;
      }
    }
    
    if (changed) {
      this.notifyUpdate({
        type: 'MERGE',
        mergedFrom: otherState
      });
    }
  }

  // Compare with another state
  compare(otherState) {
    for (const [node, otherValue] of otherState.payload) {
      const currentValue = this.payload.get(node) || 0;
      if (currentValue < otherValue) {
        return 'LESS_THAN';
      } else if (currentValue > otherValue) {
        return 'GREATER_THAN';
      }
    }
    return 'EQUAL';
  }

  // Clone current state
  clone() {
    const newCounter = new GCounter(this.nodeId, this.replicationGroup);
    newCounter.payload = new Map(this.payload);
    return newCounter;
  }

  onUpdate(callback) {
    this.updateCallbacks.push(callback);
  }

  notifyUpdate(delta) {
    this.updateCallbacks.forEach(callback => callback(delta));
  }
}

OR-Set Implementation

class ORSet {
  constructor(nodeId, initialState = null) {
    this.nodeId = nodeId;
    this.elements = new Map(); // element -> Set of unique tags
    this.tombstones = new Set(); // removed element tags
    this.tagCounter = 0;
    
    if (initialState) {
      this.merge(initialState);
    }
    
    this.updateCallbacks = [];
  }

  // Add element to set
  add(element) {
    const tag = this.generateUniqueTag();
    
    if (!this.elements.has(element)) {
      this.elements.set(element, new Set());
    }
    
    this.elemen