Postgres has a default max connection of 100 (Postgres itself, not Railway) so if you don't require 100, I would significantly lower that, Strapi has a default of max 10 fwiw.

Am I able to configure max_connections variable?

Yes, you can, but 100 is far more than you would likely need.

Could you please provide a way to increase this number?

Our maximum spotted online was 100 people at the same time (40k people per week). So I am wondering how to calculate how many connections we need to handle big online.

I was able to setup creating backups at the moment only by setting to check postgresql availability each 5 minutes, and sometimes it have success to connect. But it doesn't look good as even when online is less than 5 people, it says that "sorry, too many clients already". Probably the thing is that they send a lot of API requests, that's why all 100 connections may be used at the same time

Increasing the connection limit of Postgres would only be a bandaid solution, the correct solution here would be to put pgbouncer in front of your database, then have Strapi connect to pgbouncer so that connections can be reused.

We have a pgbouncer template available that you can easily deploy into your project from the + New button in the top right of your project canvas.

Thank you, I will try and let you know

I have setup pgbouncer, which I believe helps, but the problem hasn't gone

Are you making sure Strapi is connecting to pgbouncer instead of directly to Postgres?

You are right

Strange, when I try to connect (via Strapi) to pgbouncer, I receive knex mistake

There seems to be an unexpected error, try again with --debug for more information

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

Strapi

PGDATABASE=railway
PGHOST=monorail.proxy.rlwy.net
PGPASSWORD=real_password
PGPORT=48270
PGUSER=postgres

Bouncer
postgres://postgres:real_password@monorail.proxy.rlwy.net:48270/railway

Postgresql

postgresql://postgres:real_password@viaduct.proxy.rlwy.net:24875/railway

I was able to connect to both via PgAdmin

Number of sessions reach 100 for both (idle sessions)

After all, it seems to me that Strapi has a built-in "pgbouncer" (knex pooling system), and don't need it

I have tried to configure 2nd pgbouncer template (by Jonathan), and the same. I am able to connect via pgAdmin, but not via Strapi (connection timeout)

Let go back to my original proposed solution, don't set the pool max at 100.

Maybe some important detail to notice: server has 6 replicas (+ 1 original server, if I am correct in counting). Not sure if it influences a lot on number of idle connections.

So, I tried to decrease max pool number from 100 to 10. And you are right - it helped. If I understand correctly, each replica creates 10 idle connections by default (that's why 66 connections opened, so it means that original server is included in replicas number and 6 servers are working, not 7). And after all, I don't see this mistake in postgresql logs "sorry, too many clients already". Now it's good.

So, my next assumption is that I need to configure max number based on number of replicas that I have. In case I would have 50 replicas, I should set max value as 2 or even 1.

My only concern that I do not understand how I can, in the future, upscale database to handle bigger online using Railway tools. If I don't need pgbouncer, and don't have built-in-solutions to do it on my own, probably the only way is contacting support for some kind of horizontal scailing of postgresql.

Railway can not horizontal scale a database but that's not needed as increasing the connection limit only involves running a few simple queries on your database.

As far as I understood, in case of need I can ask Railway support to do this queries, not on my own