node-postgres-ha

High-Availability wrapper(s) over node-postgres.

---

node-postgres-ha is a wrapper over node-postgres implemented in order to address some issues found while trying to improve application's resilience.

Many of those issues are:

• Clients not being released after network issues (so that the pool may end up with no usable clients).

• Impossibility to detect network disconnection or high latency issues.

  • Specially with no connection timeout, in which case queries last forever because they are just awaiting in the pending queue.

• Client references usable after released to the pool.

• Pools with pending client requests not resolving on pool.end() unless connection timeout defined.

• Also non released clients preventing pool.end() to resolve, even when idle, may be technically correct, but in many situations it may cause more harm than good. Now an optional client_timeout option allow to limit the time they can prevent the pool from ending (⚠️ Use with caution).

• (I'll complete the list as I remember...)

For now, node-postgres-ha oly provides an enhancenment for the Pool class implemented as a wrapper over the original node-postgres' one.

Most, if not all, of the issues it tackles, would be better addressed as issues / PR's to the node-postgres repository itself. But that would have required a lot of time.

By now, this wrapper solves the problem to me (and hopefully to other people...) while, at the same time, it may serve as a cleaner base to reason about each issue separately before moving them as issues and/or PRs to mainstream node-postgres repository.

Features

• Added new status() method to facilitate inspection.

> pool.status()
{
  max: 10,
  used: 4,
  free: 6,
  idle: 4,
  alive: 4,
  timedOut: 0,
  defunct: 0,
  pending: 0,
  connErr: false
}

• Emit an error event when the connect() method fails.

• Created new "allErrors" event type that receive:

  • All the pool's error events.

  • All its clients error events (passing also the client).

• Implemented new recover() method to wisely attempt to free clients in ended state.

• Added new option "autoRecover" (default false) which, if set to true, make that if a client acquisition fails, the recover() method automatically called and the client acquisition is retryed if succeed. It is also called on errors.

• Implemented serverIsReachable() method to check network connectivity to the server.

• Implemented a connection watching functionality that also maintain an internal "connectionError" flag that can be checked through the status() method.

• Implemented the ability to remotely cancel disconnected queries from the server after connection recovery (avoiding resource wasting to the server). This must be activated throug the "autoCancel" option.

• Added new "client_timeout" option that, if set, allow to purge timed out clients on pool.end() if they are idle.

👉 Check this repo commit messages for more details...

Setup

To use node-postgres-ha in your own project, follow below steps:

1. Install node-postgres-ha AND node-postgres:

npm install ha-pg pg

2. Use it in your code instead of original node-postgres:

ℹ️ At least by now, node-postgres-ha only provides replacement for the Pool module of node-postgres.

const {Pool} = require("ha-pg");

⚠️ Only promises API has been tested. If you want to use callbacks instead, try it at your own risk.

Contributing

Setting up for local development

1. Clone the repo.

2. Install actual node-postgres module with npm install --no-save pg.

📌 node-postgres-ha does NOT provide node-postgres as a dependency so that it not enforces any specific version.

That being said, it has been tested with version 8.12.0 connecting to a PostgreSQL 15.7 database.

3. Ensure you have a PostgreSQL instance running with SSL enabled and an empty database for tests

4. Ensure you have the proper environment variables configured for connecting to the instance.

5. Run npm run test to run the tests.

6. Additionally, you can also run the same tests using the original node-postgres instance you installed in step 2 with npm run test_mainstream to verify that they still DO NOT PASS in it.

TO-DO

Complete the tests

All forementioned features have been manually tested with the aid of this small tool among others.

For few of them I also implemented automated tests that can be passed both to the original implementation and to the wrapper.

But those involving connection issues are harder to simulate. Even thought I have ideas of how to address it but, for now, it's still pending...

Better separation of concerns

Add support for decorators (through rollup+babel) and reorganize code by issues/features as separate decorators.

This will make easier to:

• Reason about each one.

• Follow them to implement the changes in a node-postgres fork to, ideally, send PR's to integrate every enhancenment one by one.

Link mainstream node-postgres tests

Automate downloading of mainstream node-postgres tests and pass them too.

License

MIT