Intermediate LevelMongoDB & Mongoose
What are MongoDB Partial Indexes and how do they save index memory space?
❓ Interview Prompt: Explain Partial Indexes, partialFilterExpression setting, memory optimization, and index matching constraints.
Partial Indexes only index documents in a collection that satisfy a specified filter expression ('partialFilterExpression'):
Benefits:
•
Drastically reduces index file memory size and write maintenance overhead.
•
Constraint: MongoDB only uses a partial index if the query filter includes the exact condition defined in the 'partialFilterExpression'!
Code Implementation Example
typescript
import { Schema } from 'mongoose';
const userSchema = new Schema({ email: String, isVerified: Boolean });
// Index email ONLY for verified users!
userSchema.index(
{ email: 1 },
{ partialFilterExpression: { isVerified: true } }
);💡Defining a Partial Index matching verified user accounts.
🎯 Interview Key Takeaway
Use Partial Indexes to index subset records, minimizing index memory footprint and write amplification.
#Partial Index#partialFilterExpression#Optimization#Intermediate
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