Firebase Realtime Database

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概要

Firebase Realtime Database is a JSON database that syncs data in real-time across clients. Ideal for collaborative apps (shared whiteboards, multiplayer games, live chats) where changes appear instantly on all devices. Data syncs via WebSockets (vs polling = high latency). Learning: 1-2 weeks for basic setup, 4-6 weeks for production. Specialists earn 10-15% premium for shipping collaborative features competitors can't match. Note: Firestore is the modern choice for most use cases; Realtime DB is still excellent for low-latency real-time apps.

Firebase Realtime Databaseとは

Firebase Realtime Database is Google's real-time JSON database. Data is synced across all connected clients via WebSockets. Write to database on phone A, phone B and web instantly see the change. No polling, no delay. Ideal for collaborative apps where millisecond latency matters: shared documents, live chat, multiplayer games, real-time notifications. Data is organized as JSON tree. Security Rules (JSON format) control who reads/writes what. Offline support built-in: edits queue locally, sync when online.

🔧 ツール＆エコシステム

Firebase Realtime DatabaseFirebase SDKReal-time listeners and observersSecurity Rules languageFirebase EmulatorOffline supportTransaction and atomic operations

💰 地域別給与

地域	ジュニア	ミドル	シニア
USA	$70k	$112k	$165k
UK	$41k	$66k	$98k
EU	$45k	$70k	$105k
CANADA	$65k	$107k	$160k

🎓 認定資格

Firebase Realtime Database Getting Started Firebase Realtime Database Best Practices Security Rules Documentation

⚖ 比較

Firebase Mobile Platform

❓ よくある質問

What's the difference between Realtime DB and Firestore?

Realtime DB: ultra-low latency, designed for real-time sync, JSON structure (nested). Firestore: better queries, better for complex data, slightly higher latency. Use Realtime DB for real-time collaboration (chat, whiteboard); Firestore for typical apps. New projects: pick Firestore unless you need millisecond sync.

How do you handle offline edits?

Realtime DB queues edits when offline. When connection returns, it syncs automatically (merge conflicts handled). No code needed; just works.

What's a transaction in Realtime DB?

Atomic operation: read current value, compute new value, write if unchanged. Prevents race conditions. Example: increment counter (read=5, write=6). If someone else wrote 5→6 first, your transaction retries.

How do you secure Realtime DB?

Security Rules (JSON format). Example: `{"rules": {"users": {"$uid": {".": {"read": "$uid === auth.uid"}}}}}`. User can read only their own data.

Can you query Realtime DB?

Limited. Can filter by child value, limit results, order by child. Complex queries aren't possible. Complex queries = use Firestore.

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