default(now()) on the same table sometimes yield different times

[DudeRandom21]

Bug description

If there are two columns in the same table both with @default(now()) they may get slightly different times. We noticed because we have a table that has both a created datetime and an updated datetime field which are both defaulted to now at create time, but we have a constraint that updated_dt >= created_dt just as a sanity check.

I suspect this may be related to or have the same underlying cause as #12572.

How to reproduce

This is a bit tricky to reproduce given that it's a race condition.

1. Create a table with two DateTime columns with @default(now()) and using the highest level of precision.
2. Add a constraint that one column must be >= to the other (or some other method of detecting the issue).
3. Insert a row
4. Repeat step 3 until you get a failure.

Expected behavior

Any number of @default(now()) columns should all get exactly the same timestamp.

Prisma information

Here's a minimal example sufficient to see the bug
Prisma schema

model foo {
  id         Int       @id @default(autoincrement())
  created_dt DateTime? @default(now()) @db.Timestamp(6)
  updated_dt DateTime? @default(now()) @db.Timestamp(6)
}

And a test that should see the issue occurring

import { PrismaClient } from '@prisma/client';

let prismaClient = new PrismaClient();

const test = async () => {
  const f = await prismaClient.foo.create({
    data: {},
  });
  expect(f.updated_dt).toEqual(f.created_dt);
};

for (let i = 0; i < 100; i++) {
  it(`should insert a foo row: ${i}`, test);
}

On my system I see the issue about 3% or so of the time so 100 repetitions should be enough to see it, but you may need to increase the number of iterations in the loop.

Environment & setup

• OS: Ubuntu 20.04 LTS
• Database: PostgreSQL 13
• Node.js version: 14.17.6

Prisma Version

Environment variables loaded from .env
prisma                  : 3.14.0
@prisma/client          : 3.14.0
Current platform        : debian-openssl-1.1.x
Query Engine (Node-API) : libquery-engine 2b0c12756921c891fec4f68d9444e18c7d5d4a6a (at node_modules/@prisma/engines/libquery_engine-debian-openssl-1.1.x.so.node)
Migration Engine        : migration-engine-cli 2b0c12756921c891fec4f68d9444e18c7d5d4a6a (at node_modules/@prisma/engines/migration-engine-debian-openssl-1.1.x)
Introspection Engine    : introspection-core 2b0c12756921c891fec4f68d9444e18c7d5d4a6a (at node_modules/@prisma/engines/introspection-engine-debian-openssl-1.1.x)
Format Binary           : prisma-fmt 2b0c12756921c891fec4f68d9444e18c7d5d4a6a (at node_modules/@prisma/engines/prisma-fmt-debian-openssl-1.1.x)
Default Engines Hash    : 2b0c12756921c891fec4f68d9444e18c7d5d4a6a
Studio                  : 0.460.0

[Weakky]

Hey,

This issue was just fixed and will be available in the next release (4.0).

Thanks for reporting 🙏