[pgpool-general: 5559] Pgpool stops handling connections

Thomas Höll Thomas.Hoell at neos-it.de
Tue Jun 6 23:01:34 JST 2017

Hi all,

we're having a streaming replication setup as backend for one of our client's application we're hosting.
The backend consists of two virtual machines (Fedora Server 25) running PostgreSQL 9.6 and Pgpool 3.6.4 (this also happened with previous Pgpool versions).

Those machines are configured for streaming replication in master/slave mode. The Postgres-Instances are running fine, but Pgpool is giving us troubles.

After some time, Pgpool stops accepting connections. They are not rejected, the application trying to connect simply hangs. I have to stop the corresponding Pgpool-Instance
and the other takes over. The stopping itself takes forever. After some time, systemd simply kills the processes and I have to manually delete the leftover sockets.

I have absolutely no idea what's causing this. The Postgres-Instances are configured to accept up to 1000 connections, which should not be the problem.

About the application accessing the database:

There are multiple instances, each using a separate database. The application uses Activiti, which DOES NOT pool connections. So we're having a pretty high amount of
connections per second. The problem mostly occurs during peak hours, so load is most likely a factor.

I've tried plaing around with num_init_children and max_pool. Increasing max_pool and lowering num_init_children made things a lot worse.

Also, Pgpool still accepts pool join requests from other Pgpool instances, it's just that database connections aren't handled anymore.

You can find my pgpool.conf here: https://pastebin.com/4ee2bhhf


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