Where and when to use knex.destroy?

Question

I'm confused on where to use knex.destroy() in my Node API.

If I don't use knex.destroy() after I open the connection to make a call, the connection pool fills up over time, leading to error:

Unhandled rejection TimeoutError: Knex: Timeout acquiring a connection. The pool is probably full. Are you missing a .transacting(trx) call?

If I close the connection, which makes sense to me, when I'm done with it,

router.get('/users', function(req, res, next) {
    var select = knex.select('*').from('users');
    select.then((result) => {
        res.send(result);
    }).catch((error) => {
        res.send(error);
    }).finally(function() {
        knex.destroy(); // close it when I'm done
    });
});

The connection is closed for separate API calls:

Unhandled rejection Error: Unable to acquire a connection at Client_PG.acquireConnection (/var/app/current/node_modules/knex/lib/client.js:331:40)

So where and when do I actually destroy the connection? Again, this Node application simply serves as an API. Each API call should open, then close, the connection, but knex doesn't seem to like this.

---

Router files that require knex: (I do this for each router file)

const knexService = require('../knexService');
const bookshelf = knexService.bookshelf;
const knex = knexService.knex;
let User = require('../models/User');

module.exports = function(app, router) {
   router.get('/users', function(req, res, next) {
       var select = knex.select('*').from('users');
       select.then((result) => {
           res.send(result);
       }).catch((error) => {
           res.send(error);
       }).finally(function() {
           knex.destroy(); // close it when I'm done
       });
   });
   ...

UserModel file

const knexService = require('../knexService');
const bookshelf = knexService.bookshelf;
var BaseModel = require('./BaseModel');
var addressModel = require('./Address').Address;

var User = BaseModel.extend({
    tableName: 'users',
    hasTimestamps: true,
    addresses: function() {
        return this.hasMany(addressModel);
    }
});

KnexService.js

const knexfile = require('./knexfile');
const knex = require('knex')(knexfile.production);
const bookshelf = require('bookshelf')(knex);

module.exports.knex = knex;
module.exports.bookshelf = bookshelf;

KnexFile.js

module.exports = {

    development: {
        client: 'pg',
        version: '7.2',
        connection: {
            ...

Answer 1

knex.destroy() should be called when you want to knex to throw away all connections from pool and stop all timers etc. so that application can end gracefully.

So basically that should be called only on application exit unless you are doing some more complex stuff for example with connecting to multiple databases with multiple knex instances.

If you are running out of connections and pool fills up it means that you have problems in your code. Possible reasons could be:

• making too many long lasting queries concurrently
• creating transactions and never committing / rolling back so those connections are never returned to the pool
• bug in knex / bookshelf / some middleware

You should try to pinpoint which parts of your app causes pool to fill up, remove all the extra code like bookshelf related stuff and find the minimal setup which you can use to replicate your problem (also remove all transactions to start with).

Are you really using postgresql 7.2 or are you connecting some custom postgresql compatible DB? That could cause some issues, but I don't think those would reveal themselves in that way, but by having broken connections to be left in pool.