Mastering QueryCache — The Database Layer of React Query

If QueryClient is the brain, then QueryCache is the database layer that stores everything. This is where: ✅ All queries are stored ✅ State is maintained ✅ Observers are attached ✅ Garbage collection is tracked ✅ Fetch deduplication happens Let's understand QueryCache at the internal engine level 🔥 From @tanstack/react-query 📋 Table of Contents What is QueryCache? QueryCache Structure Query Object Internals Complete Query Lifecycle QueryCache Responsibilities Advanced Concepts QueryCache vs QueryClient Internal Event System Real-World Insights Performance Characteristics ⚡ Quick Summary TL;DR: QueryCache is the internal database that: ✅ Stores all Query instances as a hash map ✅ Manages query state machines ✅ Coordinates observers and notifications ✅ Handles fetch deduplication ✅ Tracks garbage collection ✅ Enables structural sharing ✅ Powers DevTools integration Length: ~25 min read | Level: Advanced 📦 Installation npm install @tanstack/react-query 🗄️ What is QueryCache? {#what-is-quer