Firestore vs Realtime Database: Which Is Best and Why?

Source: Dev.to

Firebase offers two databases:

• Realtime Database – the original JSON‑tree database
• Cloud Firestore – the newer document‑oriented database

Both sync in real time and work offline, but they’re built for different needs. Below is a quick comparison and my personal pick – and why.

---

Quick Overview

---

Realtime Database: What It Is and When It Shines

What it is – One big JSON tree. You read and write at paths such as /users/uid/profile or /chats/chatId/messages. Data is nested; listening to a path returns everything under it (or you can use shallow reads to limit depth). There’s no “query by field” – the path itself acts as the query.

Strengths

• Simple – No collections, no indexes. Just read/write paths. Great for small apps and prototypes.
• Very low latency – Direct path access makes it ideal for high‑frequency updates (e.g., presence, cursor position, live scores).
• Cheap at small scale – Storage + bandwidth pricing can be lower than Firestore’s per‑operation model when data and traffic are modest.
• Tiny SDK – Smaller bundle size, useful for constrained environments.

Weaknesses

• No real queries – You can’t “get all users where role = admin” or “messages where createdAt > X.” You must read a path and filter client‑side or denormalize heavily.
• Scaling & depth limits – Deep trees and wide fan‑out (e.g., one write that touches many nodes) don’t scale well; you may need to flatten or split data.
• Tree‑only structure – Relations and many‑to‑many are awkward, often leading to duplicated data and extra sync logic.

When I use it

• Simple real‑time apps (presence, basic chat, live counters)
• Prototypes or proofs of concept
• Situations where the data naturally forms a tree and query needs are minimal
• Projects already built on Realtime Database where migration isn’t justified

---

Firestore: What It Is and When It Shines

What it is – A document database. Data lives in collections (e.g., users, chats); each document has an ID and key‑value (and nested) data. Documents can contain subcollections (e.g., chats/chatId/messages). Queries use where, orderBy, limit, and compound indexes. Real‑time listeners work on collections or query results.

Strengths

• Rich queries – “Users where role == 'admin'”, “messages where chatId == X orderBy createdAt limit 50”. Server‑side querying and explicit indexes make complex data access easy.
• Scales better – Multi‑region, automatic scaling, no single‑tree bottleneck. Ideal for many collections and complex access patterns.
• Clearer data model – Collections and documents map well to entities and relationships, reducing the need for heavy denormalization.
• Strong offline support – Queries and listeners work offline with persistence, just like Realtime Database.

Weaknesses

• Pricing can bite – You pay per read/write/delete. Heavy read traffic (e.g., “list all items” on every screen load) can become expensive without caching or pagination.
• More setup – Indexes, security rules, and data modeling require more upfront thought than “just a path.”
• Slightly higher latency – Flexible queries involve more processing than a single‑path read, though the difference is usually negligible.

When I use it

• Most new Firebase projects
• Anything that needs filtering, pagination, or multiple views over the same data
• Apps expected to grow in data volume and query complexity

---

Side‑by‑Side: Key Differences

---

Which Is Best for You?

If you need a quick prototype, a simple real‑time feature, or you’re already deep into a Realtime Database project, stick with the Realtime Database. It’s lightweight, cheap at low scale, and offers ultra‑low latency for straightforward path reads.

If you’re building a new app that will grow, requires complex queries, pagination, or you want a clearer data model, go with Firestore. Its scalability, query capabilities, and multi‑region resilience make it the safer long‑term choice, even though you’ll need to manage pricing and indexing more carefully.

Best? My Recommendation

For most apps today: Firestore is the better default.

Reasons

• Querying – Almost every app eventually needs “get items by condition” or “ordered list with pagination.” Firestore does that natively; Realtime Database forces work‑arounds and denormalization.
• Scaling – If the app grows, Firestore scales with you. Realtime Database can hit structural limits and require big refactors.
• Data model – Documents and collections match how we think about users, chats, posts, etc. Easier to maintain and onboard others.
• Ecosystem and future – Google is investing in Firestore (multi‑region, better tooling). Realtime Database is stable but not where new features land first.

When Realtime Database is still the best choice

• Very simple real‑time only – Presence, live counters, or a tiny tree with almost no query needs. Simplicity and latency matter more than flexibility.
• Strict cost at tiny scale – You have almost no reads/writes and want the smallest bill; Realtime Database’s pricing can be lower.
• Existing Realtime Database app – Migration has a cost. If the current app is simple and stable, staying on Realtime Database is fine until you need Firestore’s query and scale.

Summary

• Use Firestore for new projects and anything that needs queries or will grow.
• Use Realtime Database for simple, path‑based real‑time apps or when you’re already on it and migration isn’t justified.

In practice, “which is best” = Firestore for most cases; Realtime Database for a narrow but real set of use cases.

Saad Mehmood — Portfolio