What does "FATAL: remaining connection slots are reserved for non-replication superuser connections" mean?

[luckow]

Today I was informed via a Cloudron notification that the Postgres service is being terminated because of this FATAL. Restarting the service helped. But I have no clue what this means. Does anyone know anything about this Postgres error?

[nebulon]

I think this means that the postgres server ran out of available connection slots in the pool, possibly due to too many clients or buggy clients. Some of those slots are apparently reserved for some admin/superuser connection, I guess to still be able to do maintenance.

Which apps do you have installed which use postgres? (I think you have to dig into the CloudronManifests to figure that)

[girish]

I finally managed to get to the bottom of this. There was a bug in the postgresql addon backup logic where connections were not closed properly. This resulted in periodic backups keeping lots of connections open. This is fixed in 6.3.