Redis & Key-Value

Q: Which Rust crate?

redis crate with async features; fred for cluster-heavy setups.

Q: Connection pool?

deadpool-redis or multiplexed connection per process.

Q: TLS?

rediss:// URL with rustls feature on client.

Q: Testing?

testcontainers Redis module or embedded mock implementing trait.

Use Redis for caches, rate-limit counters, pub/sub, and ephemeral session state alongside your primary SQL database.

Recipe

Quick-reference recipe card - copy-paste ready.

use redis::AsyncCommands;
 
let client = redis::Client::open(redis_url)?;
let mut conn = client.get_multiplexed_async_connection().await?;
let _: () = conn.set_ex("user:1:session", session_id, 3600).await?;
let cached: Option<String> = conn.get("user:1:profile").await?;

When to reach for this: Read-heavy hot keys, TTL-based eviction, distributed locks, or cross-instance pub/sub - not primary source of truth for money.

Working Example

use redis::AsyncCommands;
use serde::{Deserialize, Serialize};
 
#[derive(Serialize, Deserialize)]
struct Profile { name: String }
 
async fn cached_profile(
    conn: &mut redis::aio::MultiplexedConnection,
    user_id: u64,
    loader: impl FnOnce() -> Profile,
) -> redis::RedisResult<Profile> {
    let key = format!("profile:{user_id}");
    if let Ok(json) = conn.get::<_, String>(&key).await {
        if let Ok(p) = serde_json::from_str(&json) {
            return Ok(p);
        }
    }
    let profile = loader();
    let _: () = conn.set_ex(&key, serde_json::to_string(&profile).unwrap(), 300).await?;
    Ok(profile)
}

What this demonstrates:

Multiplexed async connection from redis crate.
Cache-aside: get JSON, on miss load and set_ex with TTL.
Serde JSON as value encoding convention.
Key naming with colon namespaces.

Deep Dive

How It Works

Redis is in-memory with optional persistence (RDB/AOF).
TTL keys auto-expire - ideal for sessions and caches.
Single-threaded server - avoid huge values and hot key storms.

Common Patterns

Pattern	Redis type	Use
Cache	String (JSON)	Profile, config
Rate limit	String INCR	Per-IP counters
Lock	String SET NX	Short critical sections
Queue	List / Stream	Simple job buffer
Pub/Sub	Channels	Cache invalidation fan-out

Rust Notes

// fred or deadpool-redis for connection pooling at scale

Gotchas

Cache as source of truth - Data loss on flush loses money records. Fix: SQL authoritative; Redis cache only.
No TTL - Keys grow until OOM. Fix: Always set TTL on cache entries.
Thundering herd - Cache miss stampede on hot key. Fix: Single-flight lock or stale-while-revalidate.
Large JSON blobs - Blocks Redis single thread. Fix: Keep values small; chunk or use SQL for big payloads.
Pub/sub reliability - Fire-and-forget, no persistence. Fix: Use Redis Streams or message broker for jobs.

Alternatives

Alternative	Use When	Don't Use When
In-process moka cache	Single instance, microsecond latency	Multi-instance consistency needed
Memcached	Simple TTL cache only	Pub/sub, structures, persistence
PostgreSQL UNLOGGED	Small team, one database	Dedicated cache tier already exists

FAQs

Which Rust crate?

redis crate with async features; fred for cluster-heavy setups.

Connection pool?

deadpool-redis or multiplexed connection per process.

Cluster mode?

Use cluster-aware client; hash tags for multi-key ops.

TLS?

rediss:// URL with rustls feature on client.

Serialization?

JSON for debuggability; MessagePack for size at scale.

Invalidate cache?

Pub/sub channel or version suffix in key on writes.

Rate limiting?

INCR with EXPIRE window - see Rate Limiting page.

Session store?

Random session ID key with TTL; store user ID as value.

Testing?

testcontainers Redis module or embedded mock implementing trait.

GDPR delete?

Track key patterns per user; delete by SCAN prefix on account erasure.

Connection Pooling - Redis pools
Databases Basics - SQL + cache split
Rate Limiting & Abuse Prevention - Redis counters
Authentication & Sessions - Session storage
Databases Best Practices - Cache discipline

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.

Recipe

Quick-reference recipe card - copy-paste ready.

use redis::AsyncCommands;
 
let client = redis::Client::open(redis_url)?;
let mut conn = client.get_multiplexed_async_connection().await?;
let _: () = conn.set_ex("user:1:session", session_id, 3600).await?;
let cached: Option<String> = conn.get("user:1:profile").await?;

When to reach for this: Read-heavy hot keys, TTL-based eviction, distributed locks, or cross-instance pub/sub - not primary source of truth for money.

Working Example

use redis::AsyncCommands;
use serde::{Deserialize, Serialize};
 
#[derive(Serialize, Deserialize)]
struct Profile { name: String }
 
async fn cached_profile(
    conn: &mut redis::aio::MultiplexedConnection,
    user_id: u64,
    loader: impl FnOnce() -> Profile,
) -> redis::RedisResult<Profile> {
    let key = format!("profile:{user_id}");
    if let Ok(json) = conn.get::<_, String>(&key).await {
        if let Ok(p) = serde_json::from_str(&json) {
            return Ok(p);
        }
    }
    let profile = loader();
    let _: () = conn.set_ex(&key, serde_json::to_string(&profile).unwrap(), 300).await?;
    Ok(profile)
}

What this demonstrates:

Multiplexed async connection from redis crate.
Cache-aside: get JSON, on miss load and set_ex with TTL.
Serde JSON as value encoding convention.
Key naming with colon namespaces.

Deep Dive

How It Works

Redis is in-memory with optional persistence (RDB/AOF).
TTL keys auto-expire - ideal for sessions and caches.
Single-threaded server - avoid huge values and hot key storms.

Common Patterns

Pattern	Redis type	Use
Cache	String (JSON)	Profile, config
Rate limit	String INCR	Per-IP counters
Lock	String SET NX	Short critical sections
Queue	List / Stream	Simple job buffer
Pub/Sub	Channels	Cache invalidation fan-out

Rust Notes

// fred or deadpool-redis for connection pooling at scale

Gotchas

Cache as source of truth - Data loss on flush loses money records. Fix: SQL authoritative; Redis cache only.
No TTL - Keys grow until OOM. Fix: Always set TTL on cache entries.
Thundering herd - Cache miss stampede on hot key. Fix: Single-flight lock or stale-while-revalidate.
Large JSON blobs - Blocks Redis single thread. Fix: Keep values small; chunk or use SQL for big payloads.
Pub/sub reliability - Fire-and-forget, no persistence. Fix: Use Redis Streams or message broker for jobs.

Alternatives

Alternative	Use When	Don't Use When
In-process moka cache	Single instance, microsecond latency	Multi-instance consistency needed
Memcached	Simple TTL cache only	Pub/sub, structures, persistence
PostgreSQL UNLOGGED	Small team, one database	Dedicated cache tier already exists

FAQs

Which Rust crate?

redis crate with async features; fred for cluster-heavy setups.

Connection pool?

deadpool-redis or multiplexed connection per process.

Cluster mode?

Use cluster-aware client; hash tags for multi-key ops.

TLS?

rediss:// URL with rustls feature on client.

Serialization?

JSON for debuggability; MessagePack for size at scale.

Invalidate cache?

Pub/sub channel or version suffix in key on writes.

Rate limiting?

INCR with EXPIRE window - see Rate Limiting page.

Session store?

Random session ID key with TTL; store user ID as value.

Testing?

testcontainers Redis module or embedded mock implementing trait.

GDPR delete?

Track key patterns per user; delete by SCAN prefix on account erasure.

Connection Pooling - Redis pools
Databases Basics - SQL + cache split
Rate Limiting & Abuse Prevention - Redis counters
Authentication & Sessions - Session storage
Databases Best Practices - Cache discipline

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.

Redis & Key-Value

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Redis & Key-Value