Firebase Realtime vs Firestore

Firebase offers two databases — Realtime Database and Cloud Firestore. Both sync data in real time, but they differ in structure, query capabilities, pricing, and scaling behavior. Choosing the right one affects your app's performance, cost, and development complexity.

Side-by-Side Comparison

Feature              | Realtime Database      | Firestore
---------------------|------------------------|-------------------------
Data model           | JSON tree              | Collections and documents
Querying             | Simple (filter OR sort)| Rich (filter AND sort)
Full-text search     | No                     | No (use Algolia)
Offline support      | Yes                    | Yes (better on mobile)
Real-time sync       | Yes                    | Yes
Pricing              | Data transfer + size   | Per operation (read/write)
Scaling              | Single region          | Multi-region available
Transactions         | Yes (limited)          | Yes (robust)
Security rules       | JSON tree-based        | Match path-based
Best for             | Simple, fast sync      | Complex queries + scale

When to Choose Realtime Database

• You need extremely low-latency sync (multiplayer games, live cursors)
• Your data structure is simple and flat
• You transfer small amounts of data very frequently
• You are migrating an existing app that already uses it

When to Choose Firestore

• Your app needs complex queries filtering and sorting on multiple fields
• You expect significant user growth and need automatic scaling
• You want structured data with clear collection hierarchies
• You are building a new app and starting from scratch

Pricing Difference

Realtime Database charges based on storage size and data downloaded per month. Firestore charges per document read, write, and delete operation.

Realtime Database: Good when you transfer small bytes frequently
(e.g., live game coordinates — tiny data, very frequent)

Firestore: Good when reads/writes are limited but documents are large
(e.g., blog posts — each document is large, but read infrequently)

Can You Use Both?

Yes. One Firebase project can use both databases simultaneously. Some teams use Realtime Database for a live presence feature (who is online right now) and Firestore for everything else. The two databases do not share data — you manage them separately.

Key Takeaway

Choose Firestore for new projects that need complex queries and growth potential. Choose Realtime Database for apps requiring extremely fast, simple data sync or when migrating from an existing Realtime Database setup. Both databases coexist in one Firebase project, so specialized features can use whichever fits best.

Query Capability Comparison

This is the most significant practical difference between the two databases:

Realtime Database — you can do ONE of these per query:
  Filter by a value: orderByChild("score").equalTo(100)
  Sort by a value:   orderByChild("score")
  But NOT both at the same time without extra work

Firestore — you can combine freely:
  where("status", "==", "active")
  + where("score", ">", 100)
  + orderBy("score", "desc")
  + limit(10)
  All in one query

This limitation forces Realtime Database developers to either download more data than needed and filter it in JavaScript, or store data in multiple sorted lists simultaneously. Both approaches add complexity. Firestore eliminates this friction entirely.

Offline Support

Both databases support offline use — they cache data locally and sync when the connection restores. Firestore's offline support is stronger for mobile apps. It handles larger local caches, persists data across app restarts on mobile by default, and merges offline changes cleanly when reconnecting. Realtime Database's offline support is simpler but reliable for small datasets.

Location and Regional Availability

Realtime Database databases operate in a single region. Firestore offers both single-region and multi-region configurations. A multi-region Firestore database stores copies of your data in multiple Google Cloud regions, protecting against single-region outages. This makes Firestore a better choice for apps that require high availability.

Realtime Database:
  Data lives in: one selected region
  Outage in that region = your database is unavailable

Firestore (multi-region):
  Data lives in: multiple regions simultaneously
  Outage in one region = other regions continue serving

Migration Path

Migrating from Realtime Database to Firestore requires restructuring your data model from a JSON tree to a collection-document structure and rewriting your query code. Firebase does not provide an automatic migration tool. Export your Realtime Database data as JSON, write a migration script that reads the JSON and writes it into Firestore collections, and update your app code to use the Firestore SDK.

Many teams run both databases in parallel during migration — new features use Firestore while old features still use Realtime Database — then migrate the old features one by one until Realtime Database can be decommissioned.

Key Takeaway

Choose Firestore for new projects. It supports richer queries, scales better globally, offers multi-region availability, and integrates more naturally with complex app data models. Choose Realtime Database when you need extremely low-latency sync for simple JSON data, or when you are maintaining an existing app already built on it. Use both in the same Firebase project when a specific feature genuinely benefits from Realtime Database's speed while the rest of the app uses Firestore.