Approach to Sync Local DB with Cloud - Need Help

[Tholkappiar]

I'm building a local-first chat app where data syncs one-way from the cloud to the client (data is only pulled from the cloud, not pushed back). The app has multiple related tables, and I'm concerned about how to manage syncing these tables without causing partial updates or redundant syncs.

Currently, I am syncing all tables every time something changes in the cloud (such as chat message updates). Is this an optimal approach, or should I consider a better solution?

I'm using a custom useEffect hook to handle the sync process, and I invoke this hook multiple times for each function that needs syncing. Here's the current implementation:

useEffect(() => {
    if (remoteData === undefined || isSyncingRef.current) return;

    const performSync = async () => {
        isSyncingRef.current = true;
        setSyncState({ isLoading: true, error: null });

        try {
            await syncData();  // Sync function that pulls all data , (synchronize function by watermelonDB)
            setSyncState({ isLoading: false, error: null });
        } catch (error) {
            setSyncState({
                isLoading: false,
                error:
                    error instanceof Error ? error.message : "Sync failed",
            });
        } finally {
            isSyncingRef.current = false;
        }
    };

    performSync();
}, [remoteData]);

[tom-at-pixel]

You should pass lastPulledAt to your back-end (WatermelonDB's synchronize function provides this) so your back-end only returns the newly created/updated/deleted data. I use postgresql and set up triggers to automatically update created_at and updated_at fields and move deleted rows to a <table_name>_deleted table, all in the back-end. I provide a simple pull_changes(last_pulled_at) postgresql function that I call from the client using an RPC. That way, the client just passes lastPulledAt from WatermelonDB and receives only the changed data. Pulling ALL data every time isn't very scalable (might be fine for a demo app, but not for a production app). 😊

[Tholkappiar]

Thanks @tom-at-pixel , Nice approach : )

[tom-at-pixel]

You're welcome!! I suggest basing your implementation off of Synchronization, ignoring the push-related things. I tried push but with conflicts it was such a big mess. Much better to do writes directly to the server (using transactions on the back-end) and have the client just pull data after every write, IMO.

[Tholkappiar]

haha, make sense @tom-at-pixel - syncing itself is a mess when it comes to more reliable and detailing things ! and i have to mention that i been doing the same thing implemented the pull part (one way for now) have to start the push part later

[126punith]

Hello,

I've faced similar challenges with syncing multiple related tables and preventing redundant syncs. Your current approach of syncing all tables on every change can indeed lead to performance issues and unnecessary API calls. Let me share a solution that addresses these concerns.

Problems with Current Approach

1. Redundant Syncs: Syncing all tables every time any change occurs wastes bandwidth and battery
2. Partial Updates Risk: Multiple useEffect hooks can trigger overlapping syncs, causing partial/inconsistent state
3. No Caching: Every sync hits the network, even if data hasn't changed
4. Race Conditions: Multiple sync operations can interfere with each other

Solution: Smart Caching + Event-Based Sync

I've built react-native-sync-vault which solves these exact problems. Here's how it addresses your use case:

1. Smart Caching to Prevent Redundant Syncs

The package includes intelligent caching that prevents unnecessary API calls:

import { useOfflineQuery } from 'react-native-sync-vault';

function ChatMessages() {
  // Automatically caches responses and prevents redundant syncs
  const { data, isLoading, isStale } = useOfflineQuery('/api/chat/messages', {
    ttl: 5 * 60 * 1000, // 5 minutes - only syncs if cache is stale
    staleWhileRevalidate: true, // Returns cached data immediately, syncs in background
  });

  // Data is automatically cached - no redundant syncs!
  // Only syncs when:
  // - Cache is expired (based on TTL)
  // - Explicitly refetched
  // - Network reconnects (optional)
}

Benefits:

• ✅ Per-endpoint TTL: Different cache durations for different tables
• ✅ Automatic cache invalidation: Only syncs when data is actually stale
• ✅ Stale-while-revalidate: Returns cached data immediately, syncs in background
• ✅ No redundant API calls: Cache hit = no network request

2. Preventing Partial Updates with Batch Sync

Instead of syncing tables independently, you can batch related tables together:

import { useOfflineQueue } from 'react-native-sync-vault';

function ChatSyncManager() {
  const queue = useOfflineQueue({
    baseUrl: 'https://api.example.com',
    cache: {
      enabled: true,
      strategies: {
        '/api/chat/messages': { ttl: 5 * 60 }, // 5 min
        '/api/chat/users': { ttl: 15 * 60 }, // 15 min
        '/api/chat/rooms': { ttl: 30 * 60 }, // 30 min
      },
    },
  });

  // Sync related tables together to prevent partial updates
  const syncChatData = async () => {
    // All requests are batched and processed together
    const [messages, users, rooms] = await Promise.all([
      fetch('/api/chat/messages').then(r => r.json()),
      fetch('/api/chat/users').then(r => r.json()),
      fetch('/api/chat/rooms').then(r => r.json()),
    ]);

    // Update WatermelonDB with all data atomically
    await database.write(async () => {
      // Update all tables in a single transaction
      // This prevents partial updates
    });
  };
}

3. Event-Based Sync Instead of useEffect

Replace multiple useEffect hooks with event-based sync that's more efficient:

import { useOfflineQuery } from 'react-native-sync-vault';
import QueueManager from 'react-native-sync-vault';

function ChatApp() {
  // Instead of useEffect, use event-based sync
  const messages = useOfflineQuery('/api/chat/messages', {
    ttl: 5 * 60 * 1000,
    refetchOnReconnect: true, // Auto-refetch when network reconnects
  });

  const users = useOfflineQuery('/api/chat/users', {
    ttl: 15 * 60 * 1000,
  });

  // Listen to sync events instead of polling
  useEffect(() => {
    const handleSyncComplete = () => {
      // Sync completed - update UI if needed
      console.log('Sync completed');
    };

    QueueManager.on('sync:completed', handleSyncComplete);
    
    return () => {
      QueueManager.off('sync:completed', handleSyncComplete);
    };
  }, []);

  // No need for isSyncingRef or manual state management!
  // The hooks handle everything automatically
}

4. One-Way Sync (Cloud → Client)

Perfect for your use case - the package handles one-way sync elegantly:

import { useOfflineQuery } from 'react-native-sync-vault';

function ChatDataSync() {
  // One-way sync: only GET requests, no mutations
  const messages = useOfflineQuery('/api/chat/messages', {
    ttl: 5 * 60 * 1000,
    staleWhileRevalidate: true,
  });

  const users = useOfflineQuery('/api/chat/users', {
    ttl: 15 * 60 * 1000,
  });

  const rooms = useOfflineQuery('/api/chat/rooms', {
    ttl: 30 * 60 * 1000,
  });

  // Data is automatically cached and only synced when stale
  // No redundant syncs, no partial updates
}

5. Integration with WatermelonDB

Use react-native-sync-vault for network sync, WatermelonDB for local storage:

import { useOfflineQuery } from 'react-native-sync-vault';
import { database } from './watermelondb';

function ChatSync() {
  const { data: messagesData, isLoading } = useOfflineQuery('/api/chat/messages', {
    ttl: 5 * 60 * 1000,
  });

  // Sync to WatermelonDB when data arrives
  useEffect(() => {
    if (messagesData && !isLoading) {
      database.write(async () => {
        // Update WatermelonDB with synced data
        // All updates happen atomically - no partial updates
      });
    }
  }, [messagesData, isLoading]);

  // Benefits:
  // - Network layer: react-native-sync-vault (caching, sync management)
  // - Local storage: WatermelonDB (relationships, queries)
  // - No redundant syncs (smart caching)
  // - No partial updates (atomic WatermelonDB writes)
}

Key Advantages Over Your Current Approach

Current Approach	react-native-sync-vault
Syncs all tables every time	Only syncs when cache is stale
Multiple useEffect hooks	Single event-based system
Manual isSyncingRef management	Automatic state management
Risk of partial updates	Atomic batch operations
No caching	Intelligent per-endpoint caching
Redundant API calls	Cache prevents redundant calls

Recommended Setup for Your Chat App

import { useOfflineQuery } from 'react-native-sync-vault';

function ChatApp() {
  // Messages sync frequently (5 min cache)
  const messages = useOfflineQuery('/api/chat/messages', {
    ttl: 5 * 60 * 1000,
    staleWhileRevalidate: true,
  });

  // Users sync less frequently (15 min cache)
  const users = useOfflineQuery('/api/chat/users', {
    ttl: 15 * 60 * 1000,
  });

  // Rooms sync even less frequently (30 min cache)
  const rooms = useOfflineQuery('/api/chat/rooms', {
    ttl: 30 * 60 * 1000,
  });

  // Sync to WatermelonDB when data arrives
  useEffect(() => {
    if (messages.data) {
      // Update WatermelonDB messages table
    }
  }, [messages.data]);

  useEffect(() => {
    if (users.data) {
      // Update WatermelonDB users table
    }
  }, [users.data]);

  // No redundant syncs, no partial updates, no race conditions!
}

Additional Features

• ✅ Resource-Aware Sync: Reduces sync frequency when battery is low
• ✅ Network Quality Detection: Adjusts sync behavior based on connection quality
• ✅ Background Sync: Syncs survive app kills
• ✅ Event-Based Updates: Reactive hooks update UI automatically
• ✅ Offline Support: Queues requests when offline, syncs when online

Installation

npm install react-native-sync-vault

Documentation: https://github.com/126punith/react-native-sync-vault

This approach eliminates redundant syncs through smart caching, prevents partial updates through atomic operations, and replaces multiple useEffect hooks with a cleaner event-based architecture. It's specifically designed for one-way sync scenarios like yours.

I hope this helps! If you have questions about integrating it with your WatermelonDB setup, feel free to ask.

Best regards

[lucaswitch]

About pull chances:
What not use http cache instead? Its more efficient.