“using stale statistics instead of current ones because stats collector is not responding”

My postgresql 9.5 logs shows every minute the message:

using stale statistics instead of current ones because stats collector is not responding

Except a post on serverfault which is not helpfull and seems related to standby databases setup (which is not my case), I don’t find anything to solve this.

What’s the meaning of this? How can I solve that?

Additional information based on Greda’s reply:

• I have 4 CPU, and in routine less than 5% of 1 CPU is used
• I have 32Gb RAM, and in routine ~ 500Mb are used
• This is not a VM
• This runs Ubuntu 14.04.3 LTS/Linux 3.13.0 SMB x86/64

I have also tried to tweak the postgresql.conf parameters as follows

• shared_buffers: 1024MB
• work_mem: 10MB
• maintenance_work_mem: 1024MB
• effective_cache_size: 4GB

The error message is still there.

P.S: I fully understand that’s not a severe error, but it floods my logs, and I have the fear to not see important messages…

Some additional observation:

• VACUUM FULL VERBOSE ANALYZE doesn’t helps
• I have a never ending proccess connected to the database. When this is running, the VACUUM FULL VERBOSE ANALYZE seems blocked.

Can that never ending process be the root causes of my problem? In that case, since I need to have that proccess running, do I have to tweak something on the server?

Edit:

I had a never ending process connected to the db. I’ve tried to stop it, and it doesn’t helps.

My postgresql.conf file is available there