Redis Overview: Features, Data Types, Commands, Persistence, Replication, Pub/Sub and Transactions

Redis Overview

Redis is a free, open‑source, BSD‑licensed, high‑performance key‑value database.

Key Advantages

Extremely fast: read speed up to 110,000 ops/s, write speed up to 81,000 ops/s.

Rich data structures: strings, lists, hashes, sets, and sorted sets.

Atomic operations: each command is atomic; multi‑command transactions are supported via MULTI and EXEC.

Additional features: publish/subscribe, key expiration, etc.

Data Types

String : binary‑safe, can store any data (e.g., images, serialized objects) up to 512 MB per key.

127.0.0.1:6379> set hello world
OK
127.0.0.1:6379> get hello
"world"

Hash : a collection of field‑value pairs, similar to a map; ideal for representing objects.

# hash‑key example
127.0.0.1:6379> hset hash-key sub-key1 value1
(integer) 1
127.0.0.1:6379> hset hash-key sub-key2 value2
(integer) 1
127.0.0.1:6379> hgetall hash-key
1) "sub-key1"
2) "value1"
3) "sub-key2"
4) "value2"

List : ordered collection of strings, implemented as a doubly‑linked list; supports left/right push and range queries.

127.0.0.1:6379> rpush list-key v1
(integer) 1
127.0.0.1:6379> rpush list-key v2
(integer) 2
127.0.0.1:6379> lrange list-key 0 -1
1) "v1"
2) "v2"

Set : unordered collection of unique strings, backed by a hash table; O(1) add, remove, and membership checks.

127.0.0.1:6379> sadd k1 v1
(integer) 1
127.0.0.1:6379> sadd k1 v2
(integer) 1
127.0.0.1:6379> smembers k1
1) "v2"
2) "v1"

Sorted Set (Zset) : like a set but each member has a double‑precision score; members are ordered by score.

127.0.0.1:6379> zadd zset-key 728 member1
(integer) 1
127.0.0.1:6379> zrange zset-key 0 -1 withscores
1) "member1"
2) "728"

Basic Commands

Refer to the official Redis command reference for a full list.

Publish/Subscribe

Redis Pub/Sub enables message broadcasting: publishers send messages to a channel, and all subscribed clients receive them.

127.0.0.1:6379> SUBSCRIBE redisChat
Reading messages... (press Ctrl‑C to quit)
1) "subscribe"
2) "redisChat"

127.0.0.1:6379> PUBLISH redisChat "hello world"
(integer) 1

Transactions

Redis transactions batch multiple commands between MULTI and EXEC. Commands are queued and executed atomically, but a failure of one command does not roll back earlier ones.

127.0.0.1:6379> MULTI
OK
127.0.0.1:6379> SET book-name "Mastering C++ in 21 days"
QUEUED
127.0.0.1:6379> GET book-name
QUEUED
127.0.0.1:6379> EXEC
1) OK
2) "Mastering C++ in 21 days"

Persistence

Redis offers two persistence strategies:

RDB : snapshots of the dataset at intervals; fast recovery but may lose recent writes.

AOF : appends every write command to a log; configurable sync policies (always, everysec, no) balance durability and performance.

Replication

Using SLAVEOF host port, a server can become a replica of another. Replication follows a three‑step process: master creates an RDB snapshot and streams it, replica loads the snapshot, then both exchange subsequent write commands.

Sentinel

Sentinel monitors a Redis cluster and automatically promotes a replica to master if the current master fails.

Sharding

Sharding distributes data across multiple nodes. Approaches include range‑based sharding, hash‑based sharding (e.g., CRC32 modulo node count), and deployment models such as client‑side sharding, proxy sharding, or server‑side sharding via Redis Cluster.

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