@imqueue/pg-ip-listen v1.0.3

@imqueue/pg-ip-listen

Reliable PostgreSQL LISTEN/NOTIFY with inter-process lock support

Why?

With services on scale it might be a need to make sure only single service of many similar running listening to database notifications. Here comes idea of inter process communication (IPC) locking mechanism, which would guarantee that only one process handles the notifications and if it dies, next one which is live will immediately handle listening.

This library provides exactly this functionality, utilizing a single database connection for entire logic, which is the most efficient way in terms of utilizing computing resources.

This option comes enabled by default, but may be turned off if there is a need to have only pub/sub on entire subset of running concurrent processes.

Install

As easy as:

npm i --save @imqueue/pg-listen

Usage

Create file debug.ts as follows:

import { PgPubSub } from '@imqueue/pg-ip-listen';

(async () => {
    const pubSub = new PgPubSub({
        connectionString: 'posgtres://user:pass@localhost:5432/dbname',
    });

    pubSub.on('error', console.log);
    pubSub.on('connect', () => console.log('connected'));
    pubSub.on('end', () => console.log('closed'));
    pubSub.on('message', console.log);
    pubSub.on('listen', console.log);

    await pubSub.connect();
    await pubSub.listen('TestChannel');

    setInterval(async () => {
        await pubSub.notify('TestChannel', {
            some: { json: 'object' },
            and: true,
        });
    }, 5000);
})();

Now try to run this using, for-example, ts-node REPL in a several screens:

ts-node debug.ts

You'll find that all running processes connected, but only one of them is listening. Try to kill with ^C listening process. Check other processes, you will find that one of them now listening for messages.

If you need full Pub/Sub across all processes, modify instantiation of pubSub object like this:

const pubSub = new PgPubSub({
    connectionString: 'posgtres://user:pass@localhost:5432/dbname',
    oneProcessListener: false,
});

Now re-run experiment.

Docs

git clone git@github.com:imqueue/pg-ip-listen.git
cd pg-ip-listen
npm i
npm run doc

License

ISC

Happy Coding!