Redis Basics

Page 1 of 6

Data Caching with Redis

Query

• Collection Scan and Index Scan:
  • Not possible for everything → Not feasible for all scenarios.
  • Also, there are fallbacks.

Thus, there should be another way to handle caching efficiently.

---

Diagram: Query Flow

flowchart LR
    Browser -->|Query App| LocalMachine
    LocalMachine --> CacheServer
    CacheServer --> MongoDB
    CacheServer -->|Has this query been executed before?| CacheServer
    CacheServer -->|Store result of query| CacheServer

---

Caching Query Layer

Redis:

• Redis is an in-memory data structure store used as a database cache and message broker.

---

Diagram: Redis Caching Layer

flowchart LR
    Browser -->|Query App| LocalMachine
    LocalMachine -->|MongoDB| Server
    Server --> Redis
    Redis -->|Server| MongoDB

---

Node-Redis (Node.js Implementation of Redis)

// Setting values in Redis
set('key', 'value');

// Getting values from Redis
get('key', (err, val) => console.log(val));

---

Page 2 of 6

Storing Objects in Redis

// Example of storing objects
client.set('key', JSON.stringify({ read: 'topic' }));
client.get('key', (err, val) => console.log(JSON.parse(val)));

Key Data Types:

• Strings only.
• Class Sets and Hashes are also allowed.

---

MongoDB Queries with Redis Cache

const redis = require('redis');
const redisUrl = "redis://127.0.0.1:6379"; // Redis URL
const client = redis.createClient(redisUrl);
const util = require("util");

client.get = util.promisify(client.get);

const cachedBlogs = client.get(req.user.id); // Fetch cached data
if (cachedBlogs) {
    return res.send(cachedBlogs);
} else {
    const blogs = await Blog.find({ user: req.user.id });
    res.send(blogs);
    client.set(req.user.id, JSON.stringify(blogs)); }

---

Page 3 of 6

Caching Issues

1. Integration:

   • I don't think this is a good idea → Better integration with Mongoose's query generation and execution processes.

2. Timeout:

   • Cache never expires; add timeout to values assigned to Redis.

   set('key', 'value', 'EX', 10); // Expires after 10 seconds

3. Cache Keys:

   • Generate robust keys for caching.

   const key = JSON.stringify({
       query: this.getQuery(),
       collection: this.mongooseCollection.name
   });

---

Problem 2

• Use a top-level ID to hash keys or anything specific to the application domain.

---

Page 4 of 6

Redis Commands Overview

Strings

• SET key value
• APPEND
• GET
• DEL
• MSET key1 value1 key2 value2

---

Lists

• LINSERT

---

Hashes

• HSET key field value
• HGET key field
• HMGETALL
• HDEL
• HEXISTS
• HVALUES

---

Options

1. NX → Only set if doesn't exist.
2. EX → Expire after seconds.
3. PX → Expire after milliseconds.
4. keepTTL → Keep expiration (default?).

---

Numbers

• DECR, DECRBY, INCRBYFLOAT, INCR, INCRBY.

---

Sets

• SADD key value → Add.
• SREM → Remove.
• SMEMBERS → List all members of the set.
• SSCAN → Scan the set.

---

Page 5 of 6

Set Operations: Union, Intersection, Difference

Commands:

• SUNION:

  key1, key2, key3

• SINTER:

  key1, key2, key3

• SDIFF:

  [key1]
  key2, key3

• SSTORE:

  [newKey]
  key1, key2, key3

Membership Commands:

• SISMEMBER:

  [key] value  
  1 if true, 0 if not

• SMISMEMBER:

  [key] value1, value2  
  (array)

• SCARD:

  No. of elements in set

---

Sorted Sets

Structure:

Hash + Sets (Unique)  
key → member → score (integer)  
Sorted from least to greatest

Example:

Commands:

• ZADD:

  [key] [score] [member]

• ZSCORE:

  [key] [member] → output as score

• ZREM:

  [key] [member]

---

Page 6 of 6

Sorted Set Operations:

• ZCARD:

  [key] → No. of elements

• ZCOUNT:

  [key] [score1] [score2]  
  No. of elements in range  
  If no equals sign: -inf +inf

• ZPOPMIN:

  [key] [count] → No. of elements to pop

• ZPOPMAX:

  [key] [count] → No. of elements to pop

• ZINCRBY:

  [key] [count] [member]

• ZRANGE:

  [key] [index1] [index2] [WITHSCORES]  
  - 0-indexed  
  - Includes [index2]

Additional Options for ZRANGE:

• REV:

  → reverse order

• LIMIT:

  → skip, output count

---

References & Related Topics

• Redis Official Documentation
• Node.js Redis Library
• Mongoose Documentation
• Advanced Node.js Techniques for Caching