"FATAL: sorry, too many clients already" postgres error in develop mode on

Bug description

I use prisma inside an api-route of https://nextjs.org/ (this is by the way an awesome setup) for a graphql-api. After some time you will get this error:

Error in connector: Error querying the database: db error: FATAL: sorry, too many clients already
    at PrismaClientFetcher.request

I guess the hot-reloading or refreshing of nextjs might mess with the connection-pool of prisma. I verified that the prisma-client that is used in the route is a singleton:

// this is imported in my api route
import { PrismaClient } from "@prisma/client";

const prisma = new PrismaClient();

export default prisma;

How to reproduce

Steps to reproduce the behavior:

1. create a file pages/api/graphql.ts inside that, use prisma client
2. it probably needs some code changes that result in a rebuilding of this file /api/graphql.ts or its imports
3. at some point you should get the error

Expected behavior

should not throw this error i guess?

Prisma information

Environment & setup

• OS: macOS
• Database: [PostgreSQL
• Prisma version: prisma2@2.0.0-preview024, binary version: 377df4fe30aa992f13f1ba152cf83d5770bdbc85
• Node.js version: v12.13.1

EDIT: Solution

as many still comment on this thead, I though it would be good to pin the solution here.

This issue happens because many platforms as nextjs (and probably nestjs as well) do hot reload of parts of your code. Usually you initialize the PrismaClient once in your application (as a singleton). But hot reload results in multiple initializations of this PrismaClient

so the solution is to kindof “cache” the client in a global variable. See this comment: https://github.com/prisma/prisma/issues/1983#issuecomment-620621213

[pantharshit00]

@cimchd You should indeed refactor it so that the code is using a single instance of the Prisma client. Every new call to new PrismaClient() will spin up a new connection pool.

@macrozone You can try the following code to make sure next js hot reloading doesn’t create a new prisma instance every hot reload:

import { PrismaClient } from "@prisma/client"

let prisma

if (process.env.NODE_ENV === "production") {
  prisma = new PrismaClient()
} else {
  if (!global.prisma) {
    global.prisma = new PrismaClient()
  }

  prisma = global.prisma
}

export default prisma

This snippet was originally posted here: https://github.com/prisma/prisma-client-js/issues/228#issuecomment-618433162

[giraffesyo]

For those having this issue, I solved it by creating a singleton:

import { PrismaClient } from '@prisma/client'

class DBClient {
  public prisma: PrismaClient
  private static instance: DBClient
  private constructor() {
    this.prisma = new PrismaClient()
  }

  public static getInstance = () => {
    if (!DBClient.instance) {
      DBClient.instance = new DBClient()
    }
    return DBClient.instance
  }
}

export default DBClient

Then wherever I used the client I did:

import DBClient from '../../database/client'
const prisma = DBClient.getInstance().prisma

You can then use it like normal.