Step-by-step articles on NoSQL & Caching, part of our Databases collection.
Showing 20 articles
Redis is an in-memory data store known for sub-millisecond responses. It's more than a key-value cache: each data structure solves a specific class of problems elegantly. Strings: cache values and counters SET page:/pricing "<html>..." EX 300 # cache for 5 min...
MongoDB stores data as JSON-like documents in collections . If you know SQL, most concepts map directly; the big shift is designing around how data is read rather than normalising everything. Vocabulary Table → collection . Row → document (stored as BSON, whic...
A cache in front of a slow database query or API can cut response times from hundreds of milliseconds to one. Getting freshness and failure behaviour right is the hard part. Cache-aside (lazy loading) async function getProduct(id) { const key = `cache:product:...
"Schemaless" doesn't mean "no design". In MongoDB, schema design starts from one question: what does the application read together? Embed when data is read together and owned by the parent { "_id": "ord_42", "customerId": 7, "status": "paid", "shippingAddress"...
When several app instances run the same scheduled job, you often want exactly one of them to do the work. A Redis lock is a simple way to coordinate. Acquire with SET NX PX import { randomUUID } from 'node:crypto'; async function acquireLock(name, ttlMs) { con...
Without an index, MongoDB scans every document in a collection ( COLLSCAN ). Indexes make queries fast, and compound index order matters as much as in SQL. Creating indexes await orders.createIndex({ customerId: 1 }); await orders.createIndex({ status: 1, crea...
Redis Streams are append-only logs with consumer groups. They sit between simple Redis lists and full message brokers like Kafka: persistent, replayable and easy to run. Producing events await redis.xAdd('orders', '*', { // '*' = auto-generated id (timestamp-s...
The aggregation pipeline processes documents through a series of stages, each transforming the output of the previous one. It's MongoDB's answer to SQL's GROUP BY , joins and reporting queries. Revenue per day const revenue = await orders.aggregate([ { $match:...
Pub/Sub lets one process publish a message to a channel and every subscribed process receive it instantly. A classic use is keeping WebSocket servers in sync. The problem it solves With three app instances behind a load balancer, user A's WebSocket might be on...
MongoDB itself is flexible about document shape. Mongoose adds schemas, validation, defaults and helpers on top of the official driver, which brings structure to application code. Defining a model import mongoose from 'mongoose'; await mongoose.connect(process...
Ranking millions of players by score with SQL means sorting large tables. A Redis sorted set keeps members ordered by score at all times, so rank queries take microseconds. Adding and updating scores await redis.zAdd('lb:global', [{ score: 1520, value: 'asha'...
Single-document updates in MongoDB have always been atomic. Since version 4.0 (replica sets) and 4.2 (sharded clusters), MongoDB also supports multi-document ACID transactions. Do you need one? Often a good document design avoids the need. Updating an order an...
For years Redis was BSD-licensed open source. In 2024 Redis (the company) switched new versions to source-available licences. In response, contributors forked the last BSD version as Valkey , hosted by the Linux Foundation. Later, Redis added the open-source A...
Change streams let your application subscribe to changes in a collection, database or entire cluster. Instead of polling, you get each insert, update and delete as it happens. Watching a collection const stream = orders.watch( [{ $match: { operationType: { $in...
Redis keeps data in memory. Whether anything survives a restart depends on its persistence settings, and the right choice depends on how you use Redis. RDB: point-in-time snapshots # redis.conf save 3600 1 # snapshot if at least 1 change in an hour save 300 10...
If your application data already lives in MongoDB, you can store embeddings in the same documents and query them with Atlas Vector Search , without running a separate vector database. Store embeddings with your documents await articles.insertOne({ title: 'Rese...
The default in-memory session store loses every session on restart and doesn't work with more than one server. Redis is the standard fix: fast, shared and with built-in expiry. Setup npm install express-session connect-redis redis import express from 'express'...
Flexible documents are great until a bug writes price: "free" or forgets a required field. MongoDB can validate documents on every insert and update, regardless of which application wrote them. Creating a collection with a validator await db.createCollection('...
Redis lives in RAM, so memory is the resource you'll manage most. Without limits, a growing cache can exhaust the server and get Redis killed. Set a limit # redis.conf maxmemory 2gb maxmemory-policy allkeys-lru Leave headroom on the machine for the OS, client...
skip() and limit() are the obvious way to paginate, but skip(100000) still walks past 100,000 documents. Range-based pagination keeps every page equally fast. Range (keyset) pagination // First page const page = await posts .find({ status: 'published' }) .sort...
