[BUG]: Too many connections error with Drizzle + MySQL2

[iamvinny]

[BUG]: Too many connections error with Drizzle + MySQL2

[iamvinny]

This happens when in development and using HMR. The connections doesn't get closed and hang. The solution is having the drizzle instance as a singleton. See this discord thread for an example solution.

Thanks, I managed to fix this issue by configuring my db.ts as follow:

import { drizzle } from "drizzle-orm/mysql2";
import mysql from "mysql2/promise";
import * as schema from "./schema";

if (!process.env.MYSQL_DATABASE_URL) {
    throw new Error('Missing DATABASE_URL');
}

// Singleton function to ensure only one db instance is created
function singleton<Value>(name: string, value: () => Value): Value {
    const globalAny: any = global;
    globalAny.__singletons = globalAny.__singletons || {};
    
    if (!globalAny.__singletons[name]) {
      globalAny.__singletons[name] = value();
    }
    
    return globalAny.__singletons[name];
}

// Function to create the database connection and apply migrations if needed
function createDatabaseConnection() {
    const poolConnection = mysql.createPool(process.env.MYSQL_DATABASE_URL!);
    return drizzle(poolConnection);
}

const db = singleton('db', createDatabaseConnection);

export { db, schema };

[Angelelz]

This happens when in development and using HMR. The connections doesn't get closed and hang. The solution is having the drizzle instance as a singleton. See this discord thread for an example solution.