Master Redis: Core Data Types, Commands, and Advanced Features Explained

What Is Redis

Redis is an open‑source, in‑memory data‑structure storage system that can serve as a database, cache, and message broker. It supports strings, hashes, lists, sets, sorted sets with range queries, bitmaps, hyperloglogs, and geospatial indexes.

Redis also provides replication, Lua scripting, LRU eviction, transactions, and various persistence levels, and offers high availability through Sentinel and automatic sharding with Cluster.

What Is NoSQL

Redis is a non‑relational NoSQL database. NoSQL emerged to address the limitations of single‑machine databases as traffic grows.

The Era of Single‑Machine Databases

When a website has low traffic, a single database can handle all requests.

Cache + Sharding

As traffic increases, a single database becomes insufficient. Adding a cache layer and splitting the database into clusters, optimizing its structure, and separating reads from writes improves performance.

In this context, caching is one use case of NoSQL; Redis, for example, can also act as a simple message queue, session store, counter, leaderboard, or friend‑relationship manager.

Redis General Commands

Below are common Redis commands independent of data type.

Key and Value Operations

Redis stores data as key‑value pairs, each key being unique.

For demonstration, string‑related commands are used.

keys

pattern

– returns all keys matching the pattern (O(n), usually replaced by

scan

in production).

dbsize – returns the number of keys stored.

exists

key

– checks if a key exists.

del

key

– deletes the specified key.

type

key

– returns the data type of the key.

rename

key newkey

– renames a key.

Expiration

Because many Redis values are used as cache, they often need an expiration time.

expire

key seconds

– sets a timeout on a key.

ttl

key

– shows remaining time;

-1

means persistent,

-2

means expired or non‑existent.

Redis Five Basic Data Types

<code>Redis has five fundamental data structures: strings, hashes, lists, sets, and sorted sets.</code>

String

set

key value

– set a value.

get

key

– get a value.

mset

key1 value1 key2 value2

– atomic batch set.

mget

key1 key2

– atomic batch get.

incr

key

– increment.

decr

key

– decrement.

incrby

key value

– increment by a number.

decrby

key value

– decrement by a number.

incrbyfloat

key floatvalue

– increment by a floating‑point number.

setnx

key value

– set only if key does not exist (used for distributed locks).

set

key value xx

– set only if key exists (update).

Hash

A hash can be seen as a small Redis, similar to a Java

HashMap

, implemented with an array of linked lists.

During rehashing, both old and new hash tables coexist until migration completes.

hset

key field value

– set a field.

hsetnx

key field value

– set if field does not exist.

hmset

key field1 value1 …

– batch set.

hget

key field

– get a field.

hmget

key field1 field2 …

– batch get.

hgetall

key

– get all fields.

hdel

key field

– delete a field.

hexists

key field

– check existence.

hlen

key

– number of fields.

hvals

key

– all values.

hkeys

key

– all fields.

hincrby

key field incr

– increment a numeric field.

hincrbyfloat

key field incr

– increment a floating‑point field.

List

Redis lists are implemented as doubly linked lists; insertion and deletion are fast, while index lookup is slower.

lpush

key item1 item2 …

– push to the left (stack).

rpush

key item1 item2 …

– push to the right.

lpop

key

– pop from the left.

rpop

key

– pop from the right.

lindex

key index

– get element by index (O(n)).

lrange

key start end

– get a range of elements (O(n)).

linsert

key before|after pivot value

– insert relative to an element.

lrem

key count value

– remove elements matching value.

ltrim

key start end

– keep only a range.

lset

key index value

– set element at index.

blpop

key timeout

– block until element available (0 = forever).

brpop

key timeout

– same for right side, useful for producer‑consumer.

Using left‑push/right‑pop implements a queue; left‑push/left‑pop or right‑push/right‑pop implements a stack.

Set

Redis sets behave like Java

HashSet

: unordered, no duplicate elements, useful for deduplication and set operations.

sadd

key value

– add element.

srem

key value

– remove element.

sismember

key value

– check membership.

srandmember

key count

– get random elements without removal.

spop

key count

– pop random elements (removes them).

smembers

key

– all members (O(n)).

scard

key

– cardinality.

sinter

set1 set2 …

– intersection.

sdiff

set1 set2 …

– difference.

sunion

set1 set2 …

– union.

Sorted Set (zset)

Sorted sets store members with a score, enabling ordered collections such as leaderboards.

They are implemented with skip lists, which provide fast range queries while maintaining order.

Redis Transactions and Pipelines

Pipeline

Pipelines batch multiple commands into a single network round‑trip, reducing latency. Commands in a pipeline are not atomic; they may be interleaved with other clients' commands.

Transactions

Redis transactions guarantee atomicity and isolation (A and I of ACID). Persistence depends on RDB/AOF configuration, but Redis does not provide consistency guarantees or rollback.

multi – start transaction.

exec – execute transaction.

discard – cancel queued commands.

watch

key

– monitor a key for changes before committing.

unwatch – stop monitoring.

Common Redis Commands Summary

For a concise reference, see the accompanying command summary image.