Caching in C++: Redis, Memcached, and Built-in Solutions

Caching in C++: Redis, Memcached, and Built-in Solutions

Caching is one of the key tools for optimizing the performance of C++ applications. It reduces data access time, decreases database load, and speeds up request processing. In this article, we will explore three main approaches to caching in C++: using external systems Redis and Memcached, as well as creating built-in solutions using standard containers and libraries. You will learn when to choose each approach and see practical code examples.

Why is caching needed in C++?

C++ applications often work with large volumes of data — from web servers to game engines and real-time systems. Without caching, each request can lead to expensive I/O operations or complex computations. A cache stores frequently requested data in fast memory, providing:

• Reduced latency — access to RAM is 100-1000 times faster than to disk or network.
• Reduced load — the database and external services receive fewer requests.
• Increased throughput — the application processes more requests per second.

External caching systems: Redis

What is Redis?

Redis is an in-memory key-value data store with support for complex structures (lists, sets, hashes). It runs as a separate server that the C++ application communicates with over the network. Redis is ideal for distributed systems where the cache must be shared across multiple processes or machines.

Connecting to Redis from C++

To work with Redis in C++, use the hiredis library — a minimalistic C client. Example of connecting and executing a simple request:

#include <hiredis/hiredis.h>#include <iostream>#include <string>

int main() {    // Connect to Redis on localhost:6379    redisContext *c = redisConnect("127.0.0.1", 6379);    if (c == nullptr || c->err) {        std::cerr << "Connection error: " << c->errstr << std::endl;        return 1;    }

    // Set a key    redisReply *reply = (redisReply*)redisCommand(c, "SET key %s", "value_cpp");    freeReplyObject(reply);

    // Get the value    reply = (redisReply*)redisCommand(c, "GET key");    if (reply->type == REDIS_REPLY_STRING) {        std::cout << "Value: " << reply->str << std::endl;    }    freeReplyObject(reply);

    redisFree(c);    return 0;}

Advantages and disadvantages of Redis

• + High speed (microseconds), TTL support, replication, persistence.
• + Rich set of data structures (strings, lists, hashes, bitmaps).
• - Requires a separate server and network communication.
• - Dependency on external infrastructure.

External caching systems: Memcached

What is Memcached?

Memcached is a high-performance distributed memory caching system. Unlike Redis, it supports only simple key-value pairs and has no built-in persistence. Memcached is ideal for caching SQL query results, HTML fragments, and sessions.

Connecting to Memcached from C++

For C++, use libmemcached — a popular library with a C API. Example:

#include <libmemcached/memcached.h>#include <iostream>#include <cstring>

int main() {    memcached_st *memc = memcached_create(nullptr);    memcached_server_st *servers = memcached_server_list_append(nullptr, "127.0.0.1", 11211, nullptr);    memcached_server_push(memc, serve