Implementing Parallel Database Queries with C++ Coroutines

15 Sep 2023

Coroutines

In modern applications, performing database queries efficiently is crucial for optimal performance. One way to improve query performance is by leveraging parallel processing techniques. In this blog post, we will explore how to implement parallel database queries using C++ coroutines, a powerful feature introduced in C++20.

Introduction to C++ Coroutines

C++ coroutines allow you to write asynchronous code in a more readable and sequential manner. Coroutines simplify the implementation of tasks that involve waiting for operations to complete, such as I/O operations or database queries.

To start using coroutines in C++, you need a compiler that supports the C++20 standard, such as GCC 10 or Clang 10.

Setting up the Database Connection

First, let’s set up a connection to the database using a library like SQLite. Make sure you have the necessary drivers and libraries installed.

#include <sqlite3.h>
#include <iostream>

sqlite3* db;

int main() {
    int rc = sqlite3_open("example.db", &db);
    if (rc) {
        std::cout << "Unable to open database: " << sqlite3_errmsg(db) << std::endl;
        return 1;
    }
    // Perform queries using coroutines
    sqlite3_close(db);
    return 0;
}

Implementing Parallel Database Queries with Coroutines

To make parallel queries, we can take advantage of C++20 coroutines and the co_await keyword for synchronization.

#include <sqlite3.h>
#include <iostream>
#include <experimental/generator>

// Generator type for async queries
using QueryResult = std::experimental::generator<std::string>;

// Coroutine for running database queries
QueryResult runQuery(const std::string& query) {
    sqlite3_stmt* stmt;
    sqlite3_prepare_v2(db, query.c_str(), -1, &stmt, nullptr);
  
    while (sqlite3_step(stmt) == SQLITE_ROW) {
        std::string result(reinterpret_cast<const char*>(sqlite3_column_blob(stmt, 0)),
                           sqlite3_column_bytes(stmt, 0));
        co_yield result;
    }
  
    sqlite3_finalize(stmt);
}

// Coroutine for running parallel queries
std::experimental::generator<QueryResult> runParallelQueries(
    const std::vector<std::string>& queries) {
    for (const auto& query : queries) {
        co_yield runQuery(query);
    }
}

int main() {
    int rc = sqlite3_open("example.db", &db);
    if (rc) {
        std::cout << "Unable to open database: " << sqlite3_errmsg(db) << std::endl;
        return 1;
    }

    std::vector<std::string> queries = {"SELECT * FROM users", "SELECT COUNT(*) FROM logs"};
    auto results = runParallelQueries(queries);

    // Process the results concurrently
    for (QueryResult& result : results) {
        for (std::string& value : result) {
            std::cout << value << std::endl;
        }
    }

    sqlite3_close(db);
    return 0;
}

Conclusion

By leveraging C++ coroutines, we can implement parallel database queries in a more readable and efficient way. The use of coroutines allows us to write asynchronous code with less complexity and better performance. With parallel database queries, we can significantly improve the overall speed and responsiveness of our applications.

#C++ #Coroutines