“error: too many connections for database 'postgres'” when trying to connect to any Postgres 13 instance

Question

My team and I are currently experiencing an issue where we can't connect to Cloud SQL's Postgres instance(s) from anything other than the psql cli tool. We get a too many connections for database "postgres" error (in PGAdmin, DBeaver, and our node typeorm/pg backend). It initially happened on our (only) Postgres database instance. After restarting, stopping and starting again, increasing machine CPU/memory proved to do nothing, I deleted the database instance entirely and created a new one from scratch.

However, after a few hours the problem came back. I know that we're not actually having too many connections as I am able to query pg_stat_activity from psql command line and see the following:

Only one of those (postgres username) connections is ours.

My coworker also can't connect at all - not even from psql cli.

If it matters, we are using PostgreSQL 13, europe-west2 (London), single zone availability, db-g1-small instance with 1.7GB memory, 10GB HDD, and we have public IP enabled and the correct IP addresses whitelisted.

I'd really appreciate if anyone has any insights into what's causing this.

EDIT: I further increased the instance size (to no longer be a shared core), and I managed to successfully connect my backend to it. However my psql cli no longer works - it appears that only the first client to connect is allowed to connect after a restart (even if it disconnects, other clients can't connect...).

Answer 1

From the error message, it is clear that the database "postgres" has a custom connection limit (set, for example, by ALTER DATABASE postgres CONNECTION LIMIT 1 ). And apparently, it is quite small. Why is everyone try to connect to that database anyway? Usually 'postgres' database is reserved for maintenance operations, and you should create other databases for daily use.

You can see the setting with:

select datconnlimit from pg_database where datname='postgres';

I don't know if the low setting is something you did, or maybe Google does it on its own for their cloud offering.

Answer 2

@jjanes had the right idea/mention.

I created another database within the Cloud SQL instance that wasn't named postgres and then it was fine.

It wasn't anything to do with maximum connection settings (as this was within Google Cloud SQL) or not closing connections (as TypeORM/pg does this already).