why mongoose version 5 is so slow ?

[Zoha]

Hi.
I started a normal project and install mongoose.
the version that was installed is 5.4.18
after creating some models ] wanted to test models with mocha .
and ] figure out that mongoose queries are too slow .
each query takes about 1 - 2 second to execute!!
I understood that if I switch to previous versions like 4.4.10 queries will work properly.
this is my simple code for test speed :

const mongoose = require('mongoose');
mongoose.Promise = global.Promise;
mongoose.connect("mongodb://localhost:27017/testdb");

let User  = mongoose.model('User', new mongoose.Schema({
    username: {
        type: String,
        required: false,
        default: '',
        min: 0,
        max: 255,
    },
    email: {
        type: String,
    }
}));

let user = new User({
    username: 'test',
    email: 'tesafdjklas@gmail.com',
});

let time = (new Date).getTime();
user.save().then(() => {
    console.log('OK :' + ((new Date).getTime() - time));
});

after execute with mongoose version 5.4.18 it prints OK :1004 -> about 1 seconds to execute
but by version 4.4.10 it prints OK :40 -> 40 ms
So . why new version is too slow ?
or if I'm doing something wrong, what is it ?

[Zoha]

I replaced :
mongoose.connect("mongodb://localhost:27017/testdb");
with :
mongoose.connect("mongodb://127.0.0.1:27017/testdb");
and it is ok now :)

[vkarpov15]

ipv4 vs ipv6: See: https://mongoosejs.com/docs/connections.html#options .